org.apache.cayenne.query

## Class MappedSelect<T>

- java.lang.Object
- - org.apache.cayenne.query.IndirectQuery
  - - org.apache.cayenne.query.AbstractMappedQuery
    - - org.apache.cayenne.query.MappedSelect<T>

- All Implemented Interfaces:
    Serializable, Query, Select<T>

      public class MappedSelect<T>
      extends AbstractMappedQuery
      implements Select<T>

  A query that represents a named parameterized selecting query stored in the mapping. The actual query is resolved during execution.
  Since:
    4.0
  See Also:
    Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected Integer` | `fetchLimit`
    `protected Integer` | `fetchOffset`
    `protected boolean` | `forceNoCache`
    `protected Integer` | `pageSize`
    `protected Class<T>` | `resultClass`
    `protected Integer` | `statementFetchSize`

    - ### Fields inherited from class org.apache.cayenne.query.AbstractMappedQuery

      `params, queryName`

    - ### Fields inherited from class org.apache.cayenne.query.IndirectQuery

      `dataMap, lastResolver, name, replacementQuery`

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `MappedSelect(String queryName)`
    `protected` | `MappedSelect(String queryName, Class<T> resultClass)`

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `ResultBatchIterator<T>` | `batchIterator(ObjectContext context, int size)` Creates a ResultBatchIterator based on the provided context and batch size.
    `protected Query` | `createReplacementQuery(EntityResolver resolver)` Creates a substitute query.
    `MappedSelect<T>` | `forceNoCache()` Forces query cache to be refreshed during the execution of this query.
    `void` | `iterate(ObjectContext context, ResultIteratorCallback<T> callback)` Creates a ResultIterator based on the provided context and passes it to a callback for processing.
    `ResultIterator<T>` | `iterator(ObjectContext context)` Creates a ResultIterator based on the provided context.
    `MappedSelect<T>` | `limit(int fetchLimit)` Resets query fetch limit - a parameter that defines max number of objects that should be ever be fetched from the database.
    `MappedSelect<T>` | `offset(int fetchOffset)` Resets query fetch offset - a parameter that defines how many objects should be skipped when reading data from the database.
    `MappedSelect<T>` | `pageSize(int pageSize)` Resets query page size.
    `MappedSelect<T>` | `param(String name, Object value)`
    `MappedSelect<T>` | `params(Map<String,?> parameters)`
    `static MappedSelect<?>` | `query(String queryName)` Loads query with the given name from the mapping configuration.
    `static <T> MappedSelect<T>` | `query(String queryName, Class<T> rootClass)` Loads query with the given name, which selects objects of a given persistent class, from the mapping configuration.
    `List<T>` | `select(ObjectContext context)` Selects objects using provided context.
    `T` | `selectFirst(ObjectContext context)` Selects a single object using provided context.
    `T` | `selectOne(ObjectContext context)` Selects a single object using provided context.
    `MappedSelect<T>` | `statementFetchSize(int statementFetchSize)` Sets fetch size of the PreparedStatement generated for this query.

    - ### Methods inherited from class org.apache.cayenne.query.AbstractMappedQuery

      `name`

    - ### Methods inherited from class org.apache.cayenne.query.IndirectQuery

      `createSQLAction, getDataMap, getMetaData, getName, getReplacementQuery, route, setDataMap, setName`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

    - ### Methods inherited from interface org.apache.cayenne.query.Query

      `createSQLAction, getDataMap, getMetaData, getName, route`

- - ### Field Detail

    - #### resultClass

          protected Class<T> resultClass

    - #### fetchLimit

          protected Integer fetchLimit

    - #### fetchOffset

          protected Integer fetchOffset

    - #### statementFetchSize

          protected Integer statementFetchSize

    - #### pageSize

          protected Integer pageSize

    - #### forceNoCache

          protected boolean forceNoCache

  - ### Constructor Detail

    - #### MappedSelect

          protected MappedSelect(String queryName)

    - #### MappedSelect

          protected MappedSelect(String queryName,
                                 Class<T> resultClass)

  - ### Method Detail

    - #### query

          public static <T> MappedSelect<T> query(String queryName,
                                                  Class<T> rootClass)

      Loads query with the given name, which selects objects of a given persistent class, from the mapping configuration.
      Parameters:
        `queryName` - name of the mapped query
        `rootClass` - the Class of objects fetched by this query

    - #### query

          public static MappedSelect<?> query(String queryName)

      Loads query with the given name from the mapping configuration.
      Parameters:
        `queryName` - name of the mapped query

    - #### limit

          public MappedSelect<T> limit(int fetchLimit)

      Resets query fetch limit - a parameter that defines max number of objects that should be ever be fetched from the database.

    - #### offset

          public MappedSelect<T> offset(int fetchOffset)

      Resets query fetch offset - a parameter that defines how many objects should be skipped when reading data from the database.

    - #### statementFetchSize

          public MappedSelect<T> statementFetchSize(int statementFetchSize)

      Sets fetch size of the PreparedStatement generated for this query. Only non-negative values would change the default size.
      See Also:
        `Statement.setFetchSize(int)`

    - #### pageSize

          public MappedSelect<T> pageSize(int pageSize)

      Resets query page size. A non-negative page size enables query result pagination that saves memory and processing time for large lists if only parts of the result are ever going to be accessed.

    - #### forceNoCache

          public MappedSelect<T> forceNoCache()

      Forces query cache to be refreshed during the execution of this query.

    - #### params

          public MappedSelect<T> params(Map<String,?> parameters)

      Overrides:
        `params` in class `AbstractMappedQuery`

    - #### param

          public MappedSelect<T> param(String name,
                                       Object value)

      Overrides:
        `param` in class `AbstractMappedQuery`

    - #### select

          public List<T> select(ObjectContext context)

      Description copied from interface: `Select`
      Selects objects using provided context.

      Essentially the inversion of "ObjectContext.select(Select)".

      Specified by:
        `select` in interface `Select<T>`

    - #### selectOne

          public T selectOne(ObjectContext context)

      Description copied from interface: `Select`
      Selects a single object using provided context. The query is expected to match zero or one object. It returns null if no objects were matched. If query matched more than one object, `CayenneRuntimeException` is thrown.

      Essentially the inversion of "ObjectContext.selectOne(Select)".

      Specified by:
        `selectOne` in interface `Select<T>`

    - #### selectFirst

          public T selectFirst(ObjectContext context)

      Description copied from interface: `Select`
      Selects a single object using provided context. The query itself can match any number of objects, but will return only the first one. It returns null if no objects were matched.

      If it matched more than one object, the first object from the list is returned. This makes 'selectFirst' different from `Select.selectOne(ObjectContext)`, which would throw in this situation. 'selectFirst' is useful e.g. when the query is ordered and we only want to see the first object (e.g. "most recent news article"), etc.

      Selecting the first object via "Select.selectFirst(ObjectContext)" is more comprehensible than selecting via "ObjectContext.selectFirst(Select)", because implementations of "Select" set fetch size limit to one.

      Specified by:
        `selectFirst` in interface `Select<T>`

    - #### iterate

          public void iterate(ObjectContext context,
                              ResultIteratorCallback<T> callback)

      Description copied from interface: `Select`
      Creates a ResultIterator based on the provided context and passes it to a callback for processing. The caller does not need to worry about closing the iterator. This method takes care of it.

      Essentially the inversion of "ObjectContext.iterate(Select, ResultIteratorCallback)".

      Specified by:
        `iterate` in interface `Select<T>`

    - #### iterator

          public ResultIterator<T> iterator(ObjectContext context)

      Description copied from interface: `Select`
      Creates a ResultIterator based on the provided context. It is usually backed by an open result set and is useful for processing of large data sets, preserving a constant memory footprint. The caller must wrap iteration in try/finally (or try-with-resources for Java 1.7 and higher) and close the ResultIterator explicitly. Or use `Select.iterate(ObjectContext, ResultIteratorCallback)` as an alternative.

      Essentially the inversion of "ObjectContext.iterator(Select)".

      Specified by:
        `iterator` in interface `Select<T>`

    - #### batchIterator

          public ResultBatchIterator<T> batchIterator(ObjectContext context,
                                                      int size)

      Description copied from interface: `Select`
      Creates a ResultBatchIterator based on the provided context and batch size. It is usually backed by an open result set and is useful for processing of large data sets, preserving a constant memory footprint. The caller must wrap iteration in try/finally (or try-with-resources for Java 1.7 and higher) and close the ResultBatchIterator explicitly.
      Specified by:
        `batchIterator` in interface `Select<T>`

    - #### createReplacementQuery

          protected Query createReplacementQuery(EntityResolver resolver)

      Description copied from class: `IndirectQuery`
      Creates a substitute query. An implementor is free to provide an arbitrary replacement query.
      Overrides:
        `createReplacementQuery` in class `AbstractMappedQuery`

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