4. Database Support
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## 4. Database Support

OpenJPA can take advantage of any JDBC 2.x compliant driver, making almost any major database a candidate for use. See our officially supported database list in Appendix 2, Supported Databases for more information. Typically, OpenJPA auto-configures its JDBC behavior and SQL dialect for your database, based on the values of your connection-related configuration properties.

If OpenJPA cannot detect what type of database you are using, or if you are using an unsupported database, you will have to tell OpenJPA what `org.apache.openjpa.jdbc.sql.DBDictionary` to use. The `DBDictionary` abstracts away the differences between databases. You can plug a dictionary into OpenJPA using the `openjpa.jdbc.DBDictionary` configuration property. The built-in dictionaries are listed below. If you are using an unsupported database, you may have to write your own `DBDictionary` subclass, a simple process.

- `access`: Dictionary for Microsoft Access. This is an alias for the `org.apache.openjpa.jdbc.sql.AccessDictionary` class.

- `db2`: Dictionary for IBM's DB2 database. This is an alias for the `org.apache.openjpa.jdbc.sql.DB2Dictionary` class.

- `derby`: Dictionary for the Apache Derby database. This is an alias for the `org.apache.openjpa.jdbc.sql.DerbyDictionary` class.

- `empress`: Dictionary for Empress database This is an alias for the `org.apache.openjpa.jdbc.sql.EmpressDictionary` class.

- `foxpro`: Dictionary for Microsoft Visual FoxPro. This is an alias for the `org.apache.openjpa.jdbc.sql.FoxProDictionary` class.

- `h2`: Dictionary for the H2 Database Engine. This is an alias for the `org.apache.openjpa.jdbc.sql.H2Dictionary` class.

- `hsql`: Dictionary for the Hypersonic SQL database. This is an alias for the `org.apache.openjpa.jdbc.sql.HSQLDictionary` class.

- `informix`: Dictionary for the Informix database. This is an alias for the `org.apache.openjpa.jdbc.sql.InformixDictionary` class.

- `ingres`: Dictionary for Ingres. This is an alias for the `org.apache.openjpa.jdbc.sql.IngresDictionary` class.

- `jdatastore`: Dictionary for Borland JDataStore. This is an alias for the `org.apache.openjpa.jdbc.sql.JDataStoreDictionary` class.

- `mariadb`: Dictionary for the MariaDB database. This is an alias for the `org.apache.openjpa.jdbc.sql.MariaDBDictionary` class.

- `mysql`: Dictionary for the MySQL database. This is an alias for the `org.apache.openjpa.jdbc.sql.MySQLDictionary` class.

- `oracle`: Dictionary for Oracle. This is an alias for the `org.apache.openjpa.jdbc.sql.OracleDictionary` class.

- `pointbase`: Dictionary for Pointbase Embedded database. This is an alias for the `org.apache.openjpa.jdbc.sql.PointbaseDictionary` class.

- `postgres`: Dictionary for PostgreSQL. This is an alias for the `org.apache.openjpa.jdbc.sql.PostgresDictionary` class.

- `soliddb`: Dictionary for IBM's SolidDB database. This is an alias for the `org.apache.openjpa.jdbc.sql.SolidDBDictionary` class.

- `sqlserver`: Dictionary for Microsoft's SQL Server database. This is an alias for the `org.apache.openjpa.jdbc.sql.SQLServerDictionary` class.

- `sybase`: Dictionary for Sybase. This is an alias for the `org.apache.openjpa.jdbc.sql.SybaseDictionary` class.

The example below demonstrates how to set a dictionary and configure its properties in your configuration file. The `DBDictionary` property uses OpenJPA's plugin syntax .

Example 4.7. Specifying a DBDictionary

    <property name="openjpa.jdbc.DBDictionary" value="hsql(SimulateLocking=true)"/>

### 4.1. DBDictionary Properties

The standard dictionaries all recognize the following properties. These properties will usually not need to be overridden, since the dictionary implementation should use the appropriate default values for your database. You typically won't use these properties unless you are designing your own `DBDictionary` for an unsupported database.

- `AllowsAliasInBulkClause`: When true, SQL delete and update statements may use table aliases.

- `ArrayTypeName`: The overridden default column type for `java.sql.Types.ARRAY`. This is used only when the schema is generated by the `mappingtool`.

- `AutoAssignClause`: The column definition clause to append to a creation statement. For example, `"AUTO_INCREMENT"` for MySQL. This property is set automatically in the dictionary, and should not need to be overridden, and is only used when the schema is generated using the `mappingtool`.

- `AutoAssignTypeName`: The column type name for auto-increment columns. For example, `"BIGSERIAL"` for PostgreSQL. This property is set automatically in the dictionary and should not need to be overridden. It is used only when the schema is generated using the `mappingtool`.

- `BatchLimit`: The default batch limit for sending multiple SQL statements at once to the database. A value of -1 indicates unlimited batching, and any positive integer indicates the maximum number of SQL statements to batch together. Defaults to 0 which disables batching.

- `BigintTypeName`: The overridden default column type for `java.sql.Types.BIGINT`. This is used only when the schema is generated by the `mappingtool`.

- `BinaryTypeName`: The overridden default column type for `java.sql.Types.BINARY`. This is used only when the schema is generated by the `mappingtool`.

- `BitTypeName`: The overridden default column type for `java.sql.Types.BIT`. This is used only when the schema is generated by the `mappingtool`.

- `BlobBufferSize`: This property establishes the buffer size in the `INSERT/UPDATE` operations with an `java.io.InputStream`. This is only used with OpenJPA's Section 7.11, “ LOB Streaming ”. Defaults to 50000.

- `BlobTypeName`: The overridden default column type for `java.sql.Types.BLOB`. This is used only when the schema is generated by the `mappingtool`.

- `BooleanRepresentation`: The overridden default representation for `java.lang.Boolean` or `boolean` fields in JPA Entities. A `org.apache.openjpa.jdbc.sql.BooleanRepresentation` describes how Boolean values in entities get mapped into the database by default. Note that you additionally might need to define the `BooleanTypeName` `BitTypeName` settings to fit your selected BooleanRepresenation.

- `BooleanTypeName`: The overridden default column type for `java.sql.Types.BOOLEAN`. This is used only when the schema is generated by the `mappingtool`.

- `CastFunction`: The SQL function call to cast a value to another SQL type. Use the tokens `{0}` and `{1}` to represent the two arguments. The result of the function is convert the `{0}` value to a `{1}` type. The default is `"CAST({0} AS {1})"`.

- `CatalogSeparator`: The string the database uses to delimit between the schema name and the table name. This is typically `"."` , which is the default.

- `CharTypeName`: The overridden default column type for `java.sql.Types.CHAR`. This is used only when the schema is generated by the `mappingtool`.

- `CharacterColumnSize`: The default size of `varchar` and `char` columns. Typically 255.

- `ClobBufferSize`: This property establish the buffer size in the `INSERT/UPDATE` operations with a `java.io.Reader`. This is only used with OpenJPA's Section 7.11, “ LOB Streaming ”. Defaults to 50000.

- `ClobTypeName`: The overridden default column type for `java.sql.Types.CLOB`. This is used only when the schema is generated by the `mappingtool`.

- `ClosePoolSQL`: A special command to issue to the database when shutting down the pool. Usually the pool of connections to the database is closed when the application is ending. For embedded databases, whose lifecycle is coterminous with the application, there may be a special command, usually `"SHUTDOWN"`, that will cause the embedded database to close cleanly. Defaults to `null`.

- `ConcatenateFunction`: The SQL function call or operation to concatenate two strings. Use the tokens `{0}` and `{1}` to represent the two arguments. The result of the function or operation is to concatenate the `{1}` string to the end of the `{0}` string. Defaults to `"({0}||{1})"`.

- `ConstraintNameMode`: When creating constraints, whether to put the constraint name before the definition (`"before"`), just after the constraint type name (`"mid"`), or after the constraint definition (`"after"`). Defaults to `"before"`.

- `CreatePrimaryKeys`: When false, do not create database primary keys for identifiers. Defaults to `true` .

- `CrossJoinClause`: The clause to use for a cross join (cartesian product). Defaults to `"CROSS JOIN"`.

- `CurrentDateFunction`: The SQL function call to obtain the current date from the database. Defaults to `"CURRENT_DATE"`.

- `CurrentTimeFunction`: The SQL function call to obtain the current time from the database. Defaults to `"CURRENT_TIME"`.

- `CurrentTimestampFunction`: The SQL function call to obtain the current timestamp from the database. Defaults to `"CURRENT_TIMESTAMP"`.

- `DateFractionDigits` Some databases support to store sub-second fraction values. The digits to store can sometimes be configured. This value defines the default number of digits to store in the database. A `dateFractionDigits=3` will e.g. lead to a `DATETIME(3)` on some databases. Note that this default can be overwritten to an integer value n per column via `@Column(scale=n)`. A `@Column(scale=-1)` will set the fraction digits to zero.

- `DatePrecision`: The database is able to store time values to this degree of precision, which is expressed in nanoseconds. This value is usually one million, meaning that the database is able to store time values with a precision of one millisecond. Particular databases may have more or less precision. OpenJPA will round all time values to this degree of precision before storing them in the database. This property can be set to one of the following precisions:

  - `DECI`: 100000000

  - `CENIT`: 10000000

  - `MILLI (default precision)`: 1000000

  - `MICRO`: 1000

  - `NANO (max precision)`: 1

- `DateMillisecondBehavior`: When retrieving a `Date` value from a database which stores the value in a TIMESTAMP column, the values retrieved will be rounded to the nearest millisecond. So a date of '2010-01-01 12:00:00.687701' stored in the database will become '2010-01-01 12:00:00.688' in the `Date` field of the entity. The following date stored in the database as '9999-12-31 23:59:59.9999' will become '10000-01-01 00:00:00.000'. This rounding may not be desirable. With this property, a user has options which will direct OpenJPA how to handle the milliseconds. This property can be set to one of the enums defined in `DBDictionary.DateMillisecondBehaviors`. The options defined in `DBDictionary.DateMillisecondBehaviors` are as follows:

  - `DateMillisecondBehaviors.ROUND`: This is the default. The `Date` will be rounded to the nearest millisecond, as described above.

  - `DateMillisecondBehaviors.DROP`: The milliseconds will be dropped, thus rounding is not performed. As an example, a date of '2010-01-01 12:00:00.687701' stored in the database will become '2010-01-01 12:00:00.000' in the `Date` field of the entity.

  - `DateMillisecondBehaviors.RETAIN`: The milliseconds will not be rounded, but will be retained. As an example, a date of '2010-01-01 12:00:00.687701' stored in the database will become '2010-01-01 12:00:00.687' in the `Date` field of the entity.

- `DateTypeName`: The overridden default column type for `java.sql.Types.DATE`. This is used only when the schema is generated by the `mappingtool`.

- `DecimalTypeName`: The overridden default column type for `java.sql.Types.DECIMAL`. This is used only when the schema is generated by the `mappingtool`.

- `DelimitedCase`: The case to use when querying the database about identifiers that have been delimited. It defaults to preserving the case of the originally specified name. Available values are: `upper, lower, preserve.`

- `DisableAlterSeqenceIncrementBy`: OpenJPA attempts to execute an ALTER SEQUENCE....INCREMENT BY SQL statement for a user defined sequence. This is done to ensure that the 'allocationSize' value defined by the entity's sequence, or default value, matches the sequence defined in the database. For example, with an allocationSize of 1000 for a sequence named 'SEQ_JPASAMPLE', the following SQL will be generated (the SQL might vary slightly depending on the databases): `ALTER SEQUENCE SEQ_JPASAMPLE INCREMENT BY 1000`. If the user executing this command doesn't have permissions to execute the command, it will fail and in turn OpenJPA will disable sequence caching. If a user wants to disable this SQL command, this property can be set to true. However, the user must ensure that the entities defined sequence is kept in synch with the sequence defined in the database. Defaults to false.

- `DisableSchemaFactoryColumnTypeErrors`: When something other than the default SchemaFactory is used, up-front mapping validation is performed against the database schema. As part of the validation, OpenJPA will verify a persistence class column's type against the column type defined in the database schema. If a mismatch is found, OpenJPA will throw an exception to flag the mismatch types and will not allow processing to continue. This can be limiting, especially if the JDBC driver and/or database can properly handle the mismatch. Set this property to true to disable column type mismatch errors. Defaults to false.

- `DistinctCountColumnSeparator`: The string the database uses to delimit between column expressions in a `SELECT COUNT(DISTINCT column-list)` clause. Defaults to `null` for most databases, meaning that multiple columns in a distinct COUNT clause are not supported.

- `DistinctTypeName`: The overridden default column type for `java.sql.Types.DISTINCT`. This is used only when the schema is generated by the `mappingtool`.

- `DoubleTypeName`: The overridden default column type for `java.sql.Types.DOUBLE`. This is used only when the schema is generated by the `mappingtool`.

- `DriverVendor`: The vendor of the particular JDBC driver you are using. Some dictionaries must alter their behavior depending on the driver vendor. Dictionaries usually detect the driver vendor and set this property themselves. See the `VENDOR_XXX` constants defined in the `DBDictionary` Javadoc for available options.

- `DropTableSQL`: The SQL statement used to drop a table. Use the token `{0}` as the argument for the table name. Defaults to `"DROP TABLE {0}"`.

- `FixedSizeTypeNames`: A comma separated list of additional database types that have a size defined by the database. In other words, when a column of a fixed size type is declared, its size cannot be defined by the user. Common examples would be `DATE`, `FLOAT`, and `INTEGER`. Each database dictionary has its own internal set of fixed size type names that include the names mentioned here and many others. Names added to this property are added to the dictionary's internal set. Defaults to `null`.

- `FloatTypeName`: The overridden default column type for `java.sql.Types.FLOAT`. This is used only when the schema is generated by the `mappingtool`.

- `ForUpdateClause`: The clause to append to `SELECT` statements to issue queries that obtain pessimistic locks. Defaults to `"FOR UPDATE"`.

- `GetStringVal`: A special function to return the value of an XML column in a select statement. For example, Oracle uses `".getClobVal()"`, as in `"SELECT t0.xmlcol.getClobVal() FROM xmltab t0"`. Defaults to the empty string.

- `InClauseLimit`: The maximum number of elements in an `IN` clause. OpenJPA works around cases where the limit is exceeded. Defaults to -1 meaning no limit.

- `IndexPhysicalForeignKeys`: Whether a search Index should automatically get created on a physical foreign key. Some databases, like MySQL, handle this internally, so we do not need to generate an explicit Index in our DDL. Other databases need an explicit serach index on foreign key columns to improve performance. IndexPhysicalForeignKeys defaults to true for Oracle, MS-SQL and PostgreSQL.

- `InitializationSQL`: A piece of SQL to issue against the database whenever a connection is retrieved from the `DataSource` .

- `InnerJoinClause`: The clause to use for an inner join. Defaults to `"INNER JOIN"`.

- `IntegerTypeName`: The overridden default column type for `java.sql.Types.INTEGER`. This is used only when the schema is generated by the `mappingtool`.

- `JavaObjectTypeName`: The overridden default column type for `java.sql.Types.JAVAOBJECT`. This is used only when the schema is generated by the `mappingtool`.

- `JoinSyntax`: The SQL join syntax to use in select statements. See Section 6, “ Setting the SQL Join Syntax ”.

- `LastGeneratedKeyQuery`: The query to issue to obtain the last automatically generated key for an auto-increment column. For example, `"SELECT LAST_INSERT_ID()"` for MySQL. This property is set automatically in the dictionary, and should not need to be overridden. If `SupportsGetGeneratedKeys` is true, the query will not be issued but a more efficient JDBC 3.0 mechanism for obtaining generated keys will be used instead.

- `LeadingDelimiter`: The characters to use as the leading delimiter for a delimited identifier. The default value is a double quote, `(")`. See Section 4.7, “ Delimited Identifiers Support ” for the default value for some specific databases.

- `LongVarbinaryTypeName`: The overridden default column type for `java.sql.Types.LONGVARBINARY`. This is used only when the schema is generated by the `mappingtool`.

- `LongVarcharTypeName`: The overridden default column type for `java.sql.Types.LONGVARCHAR`. This is used only when the schema is generated by the `mappingtool`.

- `MaxAutoAssignNameLength`: Set this property to the maximum length of the sequence name used for auto-increment columns. Names longer than this value are truncated. Defaults to 31.

- `MaxColumnNameLength`: The maximum number of characters in a column name. Defaults to 128.

- `MaxConstraintNameLength`: The maximum number of characters in a constraint name. Defaults to 128.

- `MaxEmbeddedBlobSize`: When greater than -1, the maximum size of a `BLOB` value that can be sent directly to the database within an insert or update statement. Values whose size is greater than `MaxEmbeddedBlobSize` force OpenJPA to work around this limitation. A value of -1 means that there is no limitation. Defaults to -1.

- `MaxEmbeddedClobSize`: When greater than -1, the maximum size of a `CLOB` value that can be sent directly to the database within an insert or update statement. Values whose size is greater than `MaxEmbeddedClobSize` force OpenJPA to work around this limitation. A value of -1 means that there is no limitation. Defaults to -1.

- `MaxIndexNameLength`: The maximum number of characters in an index name. Defaults to 128.

- `MaxIndexesPerTable`: The maximum number of indexes that can be placed on a single table. Defaults to no limit.

- `MaxTableNameLength`: The maximum number of characters in a table name. Defaults to 128.

- `NameConcatenator`: The value used when names are concatenated to create a generated name. The default value is the underscore `"_"`.

- `NextSequenceQuery`: A SQL string for obtaining a native sequence value. May use a placeholder of `{0}` for the variable sequence name and `{1}` for sequence increment. Defaults to a database-appropriate value. For example, `"SELECT {0}.NEXTVAL FROM DUAL"` for Oracle database.

- `NullTypeName`: The overridden default column type for `java.sql.Types.NULL`. This is used only when the schema is generated by the `mappingtool`.

- `NumericTypeName`: The overridden default column type for `java.sql.Types.NUMERIC`. This is used only when the schema is generated by the `mappingtool`.

- `OtherTypeName`: The overridden default column type for `java.sql.Types.OTHER`. This is used only when the schema is generated by the `mappingtool`.

- `OuterJoinClause`: The clause to use for an left outer join. Defaults to `"LEFT OUTER JOIN"`.

- `Platform`: The name of the database that this dictionary targets. Defaults to `"Generic"`, but all dictionaries override this value.

- `RangePosition`: Indicates where to specify in the SQL select statement the range, if any, of the result rows to be returned. When limiting the number of returned result rows to a subset of all those that satisfy the query's conditions, the position of the range clause varies by database. Defaults to 0, meaning that the range is expressed at the end of the select statement but before any locking clause. See the RANGE_XXX constants defined in `DBDictionary`.

- `RealTypeName`: The overridden default column type for `java.sql.Types.REAL`. This is used only when the schema is generated by the `mappingtool`.

- `RefTypeName`: The overridden default column type for `java.sql.Types.REF`. This is used only when the schema is generated by the `mappingtool`.

- `RequiresAliasForSubselect`: When true, the database requires that subselects in a FROM clause be assigned an alias.

- `RequiresAutoCommitForMetadata`: When true, the JDBC driver requires that autocommit be enabled before any schema interrogation operations can take place.

- `RequiresCastForComparisons`: When true, comparisons of two values of different types or of two literals requires a cast in the generated SQL. Defaults to `false`.

- `RequiresCastForMathFunctions`: When true, math operations on two values of different types or on two literals requires a cast in the generated SQL. Defaults to `false`.

- `RequiresConditionForCrossJoin`: Some databases require that there always be a conditional statement for a cross join. If set, this parameter ensures that there will always be some condition to the join clause.

- `RequiresTargetForDelete`: When true, the database requires a target for delete statements. Defaults to `false`.

- `ReservedWords`: A comma-separated list of reserved words for this database, beyond the standard SQL92 keywords.

- `SchemaCase`: The case to use when querying the database metadata about schema components. Defaults to making all names upper case. Available values are: `upper, lower, preserve`.

- `SearchStringEscape`: The default escape character used when generating SQL `LIKE` clauses. The escape character is used to escape the wildcard meaning of the `_` and `%` characters. Note: since JPQL provides the ability to define the escape character in the query, this setting is primarily used when translating other query languages, such as JDOQL. Defaults to `"\\"` (a single backslash in Java speak).

- `RequiresSearchStringEscapeForLike`: When true, the database requires an escape string for queries that use `LIKE`. The escape string can be specified using `searchStringEscape`. Defaults to `false`.

- `SelectWords`: A comma-separated list of keywords which may be used to start a SELECT statement for this database. If an application executes a native SQL statement which begins with SelectWords OpenJPA will treat the statement as a SELECT statement rather than an UPDATE statement.

- `SequenceNameSQL`: Additional phrasing to use with `SequenceSQL`. Defaults to `null`.

- `SequenceSQL`: General structure of the SQL query to use when interrogating the database for sequence names. As there is no standard way to obtain sequence names, it defaults to `null`.

- `SequenceSchemaSQL`: Additional phrasing to use with `SequenceSQL`. Defaults to `null`.

- `SimulateLocking`: Some databases do not support pessimistic locking, which will result in an exception when you attempt a transaction while using the pessimistic lock manager. Setting this property to `true` suppresses the locking of rows in the database, thereby allowing pessimistic transactions even on databases that do not support locking. At the same time, setting this property to `true` means that you do not obtain the semantics of a pessimistic transaction with the database. Defaults to `false`.

- `SmallintTypeName`: The overridden default column type for `java.sql.Types.SMALLINT`. This is used only when the schema is generated by the `mappingtool`.

- `StorageLimitationsFatal`: When true, any data truncation/rounding that is performed by the dictionary in order to store a value in the database will be treated as a fatal error, rather than just issuing a warning.

- `StoreCharsAsNumbers`: Set this property to `false` to store Java `char` fields as `CHAR` values rather than numbers. Defaults to `true`.

- `StoreLargeNumbersAsStrings`: When true, the dictionary prefers to store Java fields of type `BigInteger` and `BigDecimal` as string values in the database. Likewise, the dictionary will instruct the mapping tool to map these Java types to character columns. Because some databases have limitations on the number of digits that can be stored in a numeric column (for example, Oracle can only store 38 digits), this option may be necessary for some applications. Note that this option may prevent OpenJPA from executing meaningful numeric queries against the columns. Defaults to `false`.

- `StringLengthFunction`: Name of the SQL function for getting the length of a string. Use the token `{0}` to represent the argument.

- `StructTypeName`: The overridden default column type for `java.sql.Types.STRUCT`. This is used only when the schema is generated by the `mappingtool`.

- `SubstringFunctionName`: Name of the SQL function for getting the substring of a string.

- `SupportsAlterTableWithAddColumn`: When true, the database supports adding a new column in an ALTER TABLE statement. Defaults to `true`.

- `SupportsAlterTableWithDropColumn`: When true, the database supports dropping a column in an ALTER TABLE statement. Defaults to `true`.

- `SupportsAutoAssign`: When true, the database supports auto-assign columns, where the value of column is assigned upon insertion of the row into the database. Defaults to `false`.

- `SupportsCascadeDeleteAction`: When true, the database supports the `CASCADE` delete action on foreign keys. Defaults to `true`.

- `SupportsCascadeUpdateAction`: When true, the database supports the `CASCADE` update action on foreign keys. Defaults to `true`.

- `SupportsComments`: When true, comments can be associated with the table in the table creation statement. Defaults to `false`.

- `SupportsCorrelatedSubselect`: When true, the database supports correlated subselects. Correlated subselects are select statements nested within select statements that refers to a column in the outer select statement. For performance reasons, correlated subselects are generally a last resort. Defaults to `true`.

- `SupportsDefaultDeleteAction`: When true, the database supports the `SET DEFAULT` delete action on foreign keys. Defaults to `true`.

- `SupportsDefaultUpdateAction`: When true, the database supports the `SET DEFAULT` update action on foreign keys. Defaults to `true`.

- `SupportsDeferredConstraints`: When true, the database supports deferred constraints. The database supports deferred constraints by checking for constraint violations when the transaction commits, rather than checking for violations immediately after receiving each SQL statement within the transaction. Defaults to `true`.

- `SupportsDelimitedIdentifiers`: When true, the database supports delimited identifiers. It defaults to `true`.

- `SupportsForeignKeys`: When true, the database supports foreign keys. Defaults to `true`.

- `SupportsForeignKeysComposite`: When true, the database supports composite foreign keys. Defaults to `true`.

- `SupportsGetGeneratedKeys`: When true, OpenJPA will use `java.sql.Statement.getGeneratedKeys` method to obtain values of auto-increment columns. When false, a query specified by `LastGeneratedKeyQuery` will be used for that purpose. If not set, the value will be auto-detected by querying the JDBC driver. Setting the value to true requires that the JDBC driver supports version 3.0 or higher of the JDBC specification and supports the `java.sql.Statement.getGeneratedKeys` method.

- `SupportsHaving`: When true, the database supports HAVING clauses in selects.

- `SupportsLockingWithDistinctClause`: When true, the database supports `FOR UPDATE` select clauses with `DISTINCT` clauses.

- `SupportsLockingWithInnerJoin`: When true, the database supports `FOR UPDATE` select clauses with inner join queries.

- `SupportsLockingWithMultipleTables`: When true, the database supports `FOR UPDATE` select clauses that select from multiple tables.

- `SupportsLockingWithOrderClause`: When true, the database supports `FOR UPDATE` select clauses with `ORDER BY` clauses.

- `SupportsLockingWithOuterJoin`: When true, the database supports `FOR UPDATE` select clauses with outer join queries.

- `SupportsLockingWithSelectRange`: When true, the database supports `FOR UPDATE` select clauses with queries that select a range of data using `LIMIT`, `TOP` or the database equivalent. Defaults to `true`.

- `SupportsModOperator`: When true, the database supports the modulus operator (`%`) instead of the `MOD` function. Defaults to `false`.

- `SupportsMultipleNontransactionalResultSets`: When true, a nontransactional connection is capable of having multiple open `ResultSet` instances.

- `SupportsNullDeleteAction`: When true, the database supports the `SET NULL` delete action on foreign keys. Defaults to `true`.

- `SupportsNullTableForGetColumns`: When true, the database supports passing a `null` parameter to `DatabaseMetaData.getColumns` as an optimization to get information about all the tables. Defaults to `true`.

- `SupportsNullTableForGetImportedKeys`: When true, the database supports passing a `null` parameter to `DatabaseMetaData.getImportedKeys` as an optimization to get information about all the tables. Defaults to `false`.

- `SupportsNullTableForGetIndexInfo`: When true, the database supports passing a `null` parameter to `DatabaseMetaData.getIndexInfo` as an optimization to get information about all the tables. Defaults to `false`.

- `SupportsNullTableForGetPrimaryKeys`: When true, the database supports passing a `null` parameter to `DatabaseMetaData.getPrimaryKeys` as an optimization to get information about all the tables. Defaults to `false`.

- `SupportsNullUpdateAction`: When true, the database supports the `SET NULL` update action on foreign keys. Defaults to `true`.

- `SupportsQueryTimeout`: When true, the JDBC driver supports calls to `java.sql.Statement.setQueryTimeout`.

- `AllowQueryTimeoutOnFindUpdate`: The JPA Specification defines the javax.persistence.query.timeout, in milliseconds, as a hint to the provider. The hint is used for Query operations. This property, when set to true, will allow the query timeout hint to apply to EntityManager operations. For example, when a 'find' is executed and the resultant entity updated, the query timeout will apply to the SQL update operation. This property defaults to false.

- `SupportsRestrictDeleteAction`: When true, the database supports the `RESTRICT` delete action on foreign keys. Defaults to `true`.

- `SupportsRestrictUpdateAction`: When true, the database supports the `RESTRICT` update action on foreign keys. Defaults to `true`.

- `SupportsSchemaForGetColumns`: When false, the database driver does not support using the schema name for schema reflection on column names.

- `SupportsSchemaForGetTables`: If false, then the database driver does not support using the schema name for schema reflection on table names.

- `SupportsSelectEndIndex`: When true, the database can create a select that is limited to the first N results.

- `SupportsSelectForUpdate`: When true, the database supports `SELECT` statements with a pessimistic locking (`FOR UPDATE`) clause. Defaults to `true`.

- `SupportsSelectStartIndex`: When true, the database can create a select that skips the first N results.

- `SupportsSimpleCaseExpression`: When true, the database supports the simple form of `CASE` expression: `CASE <a> WHEN <b> THEN <c> WHEN <d> THEN <e> ELSE <f> END`. When false, the general form of `CASE` expression will be used: `CASE WHEN <a> = <b> THEN <c> WHEN <a> = <d> THEN <e> ELSE <f> END`. Defaults to `true`.

- `SupportsSubselect`: When true, the database supports subselects in queries.

- `SupportsTimestampNanos`: When true, the database supports nanoseconds with TIMESTAMP columns. Defaults to `true`.

- `SupportsUniqueConstraints`: When true, the database supports unique constraints. Defaults to `true`.

- `SupportsXMLColumn`: When true, the database supports an XML column type. See Section 7.10, “ XML Column Mapping ” for information on using this capability. Defaults to `false`.

- `SystemSchemas`: A comma-separated list of schema names that should be ignored.

- `SystemTables`: A comma-separated list of table names that should be ignored.

- `TableForUpdateClause`: The clause to append to the end of each table alias in queries that obtain pessimistic locks. Defaults to `null`.

- `tableLengthIncludesSchema`: Whether the max length for a table name includes the table's schema. Defaults to `false`.

- `TableTypes`: Comma-separated list of table types to use when looking for tables during schema reflection, as defined in the `java.sql.DatabaseMetaData.getTableInfo` JDBC method. An example is: `"TABLE,VIEW,ALIAS"`. Defaults to `"TABLE"`.

- `TimeTypeName`: The overridden default column type for `java.sql.Types.TIME`. This is used only when the schema is generated by the `mappingtool`.

- `TimestampTypeName`: The overridden default column type for `java.sql.Types.TIMESTAMP`. This is used only when the schema is generated by the `mappingtool`.

- `TinyintTypeName`: The overridden default column type for `java.sql.Types.TINYINT`. This is used only when the schema is generated by the `mappingtool`.

- `ToLowerCaseFunction`: Name of the SQL function for converting a string to lower case. Use the token `{0}` to represent the argument.

- `ToUpperCaseFunction`: SQL function call for converting a string to upper case. Use the token `{0}` to represent the argument.

- `TrailingDelimiter`: The characters to use as the trailing delimiter for a delimited identifier. The default value is a double quote, `(")`. See Section 4.7, “ Delimited Identifiers Support ” for the default value for some specific databases.

- `TrimBothFunction`: The SQL function call to trim any number of a particular character from both the start and end of a string. Note: some databases do not support specifying the character in which case only spaces or whitespace can be trimmed. Use the token `{1}` when possible to represent the character, and the token `{0}` to represent the string. Defaults to `"TRIM(BOTH {1} FROM {0})"`.

- `TrimLeadingFunction`: The SQL function call to trim any number of a particular character from the start of a string. Note: some databases do not support specifying the character in which case only spaces or whitespace can be trimmed. Use the token `{1}` when possible to represent the character, and the token `{0}` to represent the string. Defaults to `"TRIM(LEADING {1} FROM {0})"`.

- `TrimStringColumns`: When `true`, the resulting String from `ResultSet.getString` will be trimmed of trailing white space. Defaults to `false`.

- `TrimTrailingFunction`: The SQL function call to trim any number of a particular character from the end of a string. Note: some databases do not support specifying the character in which case only spaces or whitespace can be trimmed. Use the token `{1}` when possible to represent the character, and the token `{0}` to represent the string. Defaults to `"TRIM(TRAILING {1} FROM {0})"`.

- `UseGetBestRowIdentifierForPrimaryKeys`: When true, metadata queries will use `DatabaseMetaData.getBestRowIdentifier` to obtain information about primary keys, rather than `DatabaseMetaData.getPrimaryKeys`.

- `UseGetBytesForBlobs`: When true, `ResultSet.getBytes` will be used to obtain blob data rather than `ResultSet.getBinaryStream`.

- `UseGetObjectForBlobs`: When true, `ResultSet.getObject` will be used to obtain blob data rather than `ResultSet.getBinaryStream`.

- `UseGetStringForClobs`: When true, `ResultSet.getString` will be used to obtain clob data rather than `ResultSet.getCharacterStream`.

- `UseJDBC4SetBinaryStream`: When true, an attempt will be made to obtain a JDBC 4.0 version of `PreparedStatement.setBinaryStream`. When false, a `setBinaryStream` is used which takes the length of the stream. OpenJPA uses a -1 for the length since OpenJPA doesn't know the length of the stream. A few JDBC drivers check the length and throw an exception when the length is less than zero. When this property is set to true, and an applicable JDK and JDBC 4.0 driver is available, a version of `setBinaryStream` will be used which does not take a length. The default value of this property is true.

- `UseNativeSequenceCache`: This property was introduced in the 2.1.2 release to indicate (when set to `false`) that OpenJPA should not use the `CACHE` clause when creating a native sequence; instead the `INCREMENT BY` clause gets its value equal to the allocationSize property. In the 2.2.0 release, code was added to allow said functionality by default (see OPENJPA-1376). For forward compatibility, this property still remains, however it has been deprecated and will eventually be removed. Setting this property has no effect and any occurrence of it should be removed.

- `UseSchemaName`: If `false`, then avoid including the schema name in table name references. Defaults to `true` .

- `UseSetBytesForBlobs`: When true, `PreparedStatement.setBytes` will be used to set blob data, rather than `PreparedStatement.setBinaryStream`.

- `UseSetStringForClobs`: When true, `PreparedStatement.setString` will be used to set clob data, rather than `PreparedStatement.setCharacterStream`.

- `UseWildCardForCount`: When true, the JPQL `COUNT` aggregate function will be translated into SQL `COUNT(*)` expression if the SQL query does not involve joins. Defaults to `false`.

- `ValidationSQL`: The SQL used to validate that a connection is still in a valid state. For example, `"SELECT SYSDATE FROM DUAL"` for Oracle.

- `VarbinaryTypeName`: The overridden default column type for `java.sql.Types.VARBINARY`. This is used only when the schema is generated by the `mappingtool`.

- `VarcharTypeName`: The overridden default column type for `java.sql.Types.VARCHAR`. This is used only when the schema is generated by the `mappingtool`.

- `XmlTypeName`: The column type name for XML columns. This property is set automatically in the dictionary and should not need to be overridden. It is used only when the schema is generated using the `mappingtool`. Defaults to `"XML"`.

### 4.2. FirebirdDictionary Properties

The `firebird` dictionary understands the following additional properties:

- `FirebirdVersion`: The database version OpenJPA connects to. This property affects the SQL statements executed by OpenJPA. Available values are: 15, 20 and 21 - they indicate Firebird versions 1.5, 2.0 and 2.1 respectively. If not set, the value will be auto-detected.

- `IndexedVarcharMaxSizeFB15`: Firebird 1.5 imposes tight limits on index size. In particular, an indexed `VARCHAR` column size cannot exceed 252. When schema is created, OpenJPA will use this property to reduce the size of indexed `VARCHAR` columns. Defaults to 252 but you might want to decrease this value if multi-column indexes are used. If the Firebird version is 2.0 or later or schema creation is not used, this property does not matter.

- `RangeSyntax`: Firebird 2.0 and later support two ways of handling queries that select a range of data: `"FIRST <p> SKIP <q>"` and `"ROWS <m> TO <n>"`. Earlier versions support only `"FIRST <p> SKIP <q>"` syntax. This property determines the syntax to be used. Available values are: `"firstskip"` and `"rows"`. Defaults to using `"ROWS <m> TO <n>"` if the Firebird version is 2.0 or later, and `"FIRST <p> SKIP <q>"` otherwise.

### 4.3. MySQLDictionary Properties

The `mysql` dictionary also understands the following properties:

- `DateFractionDigits`: Since MySQL 5.8 a timestamp (`DATETIME`) can store up to 6 sub-second fractions. The default in MySQL and OpenJPA is 0 for backward compatibility reasons. This default can be changed by setting `DateFractionDigits` to the number of sub-second fraction digits to be stored. This will e.g. result in a `DATETIME(6)` column. The number of fraction digits to be generated can also be tweaked via the `@Column(scale=n)` annotation, where n is the number of digits. This setting has primarily an impact on the generated SQL.

- `DriverDeserializesBlobs`: Many older MySQL drivers automatically deserialize BLOBs on calls to `ResultSet.getObject`. The `MySQLDictionary` overrides the standard `DBDictionary.getBlobObject` method to take this into account. Defaults to `true` if driver version is less than 5.0, `false` otherwise. If your driver deserializes automatically, you may want to set this property to `true`.

- `TableType`: The MySQL table type to use when creating tables. Defaults to `"innodb"`.

- `UseClobs`: Some older versions of MySQL do not handle CLOBs correctly. To disable CLOB functionality, set this to `false`. Defaults to `true`.

- `OptimizeMultiTableDeletes`: MySQL as of version 4.0.0 supports multiple tables in `DELETE` statements. When this option is set, OpenJPA will use that syntax when doing bulk deletes from multiple tables. This can happen when the `deleteTableContents` `SchemaTool` action is used. (See Section 13, “ Schema Tool ” for more info about `deleteTableContents`.) Defaults to `false`, since the statement may fail if using InnoDB tables and delete constraints.

Starting with Connector/J 3.1.7, MySQL supports a variant of the driver `com.mysql.jdbc.ReplicationDriver` that automatically sends queries to a read/write master, or a failover or round-robin load balanced set of slaves based on the state of read-only status of the connection. See MySQL Reference for more details.

This replication feature can be used transparently with OpenJPA application by following configuration:

- `openjpa.ConnectionDriverName: com.mysql.jdbc.ReplicationDriver`

- `openjpa.ConnectionFactoryProperties: autoReconnect=true,roundRobinLoadBalance=true`

  OpenJPA will use a read-only connection with replicated database configuration and will automatically switch the connection to a non-readonly mode if the transaction is writing to the database.

### 4.4. OracleDictionary Properties

The `oracle` dictionary understands the following additional properties:

- `UseTriggersForAutoAssign`: When true, OpenJPA will allow simulation of auto-increment columns by the use of Oracle triggers. OpenJPA will assume that the current sequence value from the sequence specified in the `AutoAssignSequenceName` parameter will hold the value of the new primary key for rows that have been inserted. For more details on auto-increment support, see Section 4.4, “ Autoassign / Identity Strategy Caveats ” .

- `AutoAssignSequenceName`: The global name of the sequence that OpenJPA will assume to hold the value of primary key value for rows that use auto-increment. If left unset, OpenJPA will use a sequence named `"<table name>_<column name>_SEQ"`.

- `MaxEmbeddedBlobSize`: Oracle is unable to persist BLOBs using the embedded update method when BLOBs get over a certain size. The size depends on database configuration, e.g. encoding. This property defines the maximum size BLOB to persist with the embedded method. Defaults to 4000 bytes.

- `MaxEmbeddedClobSize`: Oracle is unable to persist CLOBs using the embedded update method when CLOBs get over a certain size. The size depends on database configuration, e.g. encoding. This property defines the maximum size CLOB to persist with the embedded method. Defaults to 4000 characters.

- `SupportsSetClob`: This property was used in releases previous to OpenJPA 2.2.0 to indicate that OpenJPA should attempt to use a Reader-based JDBC 4.0 method to set CLOB or XML data. It allowed XMLType and CLOB values larger than 4000 bytes to be used. For OpenJPA 2.2.0 and later releases, code was added to allow said functionality by default (see OPENJPA-1691). For forward compatibility, this property still remains, however it has been deprecated and will eventually be removed. Setting this property has no effect and any occurrence of it should be removed.

- `UseSetFormOfUseForUnicode`: Prior to Oracle 10i, statements executed against unicode capable columns (the `NCHAR`, `NVARCHAR`, `NCLOB` Oracle types) required special handling to be able to store unicode values. Setting this property to `true` (the default) will cause OpenJPA to attempt to detect when the column is one of these types, and if so, will attempt to correctly configure the statement using the `OraclePreparedStatement.setFormOfUse`. For more details, see the Oracle JDBC Programming with Unicode. Note that this can only work if OpenJPA is able to access the underlying `OraclePreparedStatement` instance, which may not be possible when using some third-party datasources. If OpenJPA detects that this is the case, a warning will be logged.

### 4.5. SybaseDictionary Properties

The `sybase` dictionary understands the following additional properties:

- `IgnoreNumericTruncation`: If true, Sybase will ignore numeric truncation on SQL operations. Otherwise, if numeric truncation is detected, the operation will fail.

### 4.6. DB2 Properties

The `db2` dictionary understands the following additional properties:

- `AppendExtendedExceptionText`: If false, OpenJPA will not call back to the database to get extended exception text.

- `SupportsRowNum`: If true, OpenJPA will use `ROWNUM` facility for range based queries that set an offset and/or limit via `setFirstResult()` and `setMaxResult()` query methods. This property must be set to `true` alongwith <lietral>SupportsSelectStartIndex</lietral> and <lietral>SupportsSelectEndIndex</lietral>. By default, `SupportsRowNum` is set to `false`. It is appropriate to set `SupportsRowNum` to `true` only when DB2 version being used is 9.7 or later.

### 4.7. Delimited Identifiers Support

OpenJPA provides support for delimited identifiers as defined in the JPA 2.0 specification. Identifiers can either be automatically delimited or individually manually delimited. To have OpenJPA automatically delimit identifiers, add the `<delimited-identifiers/>` tag to the mapping file as documented in the JPA specification.

You can manually delimit individual identifiers either in the annotations or in the definitions in the mapping file. To delimit an identifier element in an annotation, surround it with double quotes. In a mapping file, add `&quote;` to both the beginning and end of the element.

When delimited identifiers has been specified, OpenJPA will delimit SQL identifiers in the generated SQL statements. It will use database-specific delimiters as defined in the appropriate database dictionary. By default, the leading and trailing delimiters are both double quotes, `(")`. Different defaults for other dictionaries provided by OpenJPA are in the following table.

Table 4.1. Default delimiters for delimited identifiers

Dictionary | Leading Delimiter | Trailing Delimiter
--- | --- | ---
MySQLDictionary | ` | `
AccessDictionary | [ | ]
HerdDBDictionary | ` | `

Some databases support more than one set of delimiters, often based on configuration. If you need values different than the default values, you can set the `LeadingDelimiter` and the `TrailingDelimiter` dictionary properties.

You can specify whether or not the particular database that you are using supports delimited identifiers by setting the `SupportsDelimitedIdentifiers` dictionary property. If this value is set to `false`, identifiers will not be automatically delimited, even if the `<delimited-identifiers/>` tag is specified in the mapping file.

`Limitation:` The `columnDefinition` elements in identifiers are not automatically delimited by OpenJPA when using the `<delimited-identifiers/>` tag in the mapping file. If you want these to be delimited, you must manually delimit them in the annotation or mapping file definitions.

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