= Excel

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The _Excel_ module provides the ability to read from  Excel spreadsheets, which can be useful for certain use cases, eg bulk import of data.
Each row of a spreadsheet can be mapped to a domain object, usually a view model.
The view model can validate itself and then be applied.

The module also supports the opposite use case, converting a collection of domain objects into an Excel spreadsheet.

In addition, the library provides fixture support, allowing test data to be specified in a spreadsheet.



== Setup

=== Dependency Management

In your application's top level `pom.xml`, add a dependency for this module's own bill of materials (BOM):

[source,xml,subs="attributes+"]
.pom.xml
----
<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.apache.causeway.extensions</groupId>
            <artifactId>causeway-extensions-excel</artifactId>
            <scope>import</scope>
            <type>pom</type>
            <version>{page-causewayreleaseversion}</version>
        </dependency>
    </dependencies>
</dependencyManagement>
----

[#dependencies]
=== Dependencies / Imports

In the modules of your application that will use the _Excel_ extension, add dependency/ies to `pom.xml`, and update the `@Import` of the corresponding xref:userguide::modules.adoc[module]:

For xref:export-and-import[export/import]:

* add this dependency:
+
[source,xml,subs="attributes+"]
.pom.xml
----
<dependencies>
    <dependency>
        <groupId>org.apache.causeway.extensions</groupId>
        <artifactId>causeway-extensions-excel-applib</artifactId>
    </dependency>
</dependencies>
----

* and `@Import` this module:
+
[source,java]
.MyModule.java
----
@Configuration
@Import({
    CausewayModuleExtExcelApplib.class,
    // ...
})
public class MyModule { ... }
----


For xref:fixture-support[fixture support]:

* add this dependency:
+
[source,xml,subs="attributes+"]
.pom.xml
----
<dependencies>
    <dependency>
        <groupId>org.apache.causeway.extensions</groupId>
        <artifactId>causeway-extensions-excel-testing</artifactId>
    </dependency>
</dependencies>
----

* and `@Import` this module:
+
[source,java]
.MyModule.java
----
@Configuration
@Import({
    CausewayModuleExtExcelTesting.class,
    // ...
})
public class MyModule { ... }
----



[#export-and-import]
== Usage: Export and Import

Define a view model to act as a DTO.
For example:

[source,java]
----
@Named("transaction.TransactionDto")
@DomainObject(nature = Nature.VIEW_MODEL)
public class TransactionDto {
    @Getter @Setter private String customerRef;
    @Getter @Setter private LocalDate date;
    @Getter @Setter private BigDecimal amount;
}
----



It's common to define a "Manager" view model to control the process:

[source,java]
.TransactionImportExportManager.java
----
@Named("transaction.TransactionImportExportManager")
@DomainObject(nature = Nature.VIEW_MODEL)
public class TransactionImportExportManager {

    List<TransactionDto> getTransactions() { ... }  // <.>

    // ...
}
----
<.> the transactions to be exported, typically mapped from an entity into the DTO

The action to export this list of transactions would be something like:

[source,java]
.TransactionImportExportManager.java
----
@Action(semantics = SemanticsOf.SAFE)
public Blob exportToExcel(){
    return  excelService.toExcel(
            getTransactionDtos(),
            TransactionDto.class,
            "Sheet1",
            "Transactions.xlsx"
    );
}
----

And conversely, to obtain DTOs from the spreadsheet:

[source,java]
.TransactionImportExportManager.java
----
@Action(semantics = SemanticsOf.IDEMPOTENT)
@CollectionLayout(paged = -1)
public TransactionImportExportManager importFromExcel(
        @Parameter(fileAccept = ".xlsx")
        final Blob spreadsheet) {
    List<TransactionDto> transactionDtos =
        excelService.fromExcel(spreadsheet, TransactionDto.class, "Sheet1");
    ...
    return this;
}
----



[#fixture-support]
== Usage: Fixture Support

The fixture support is provided through `ExcelFixture`, an implementation of `FixtureScript` that is initialized with a spreadsheet and a set of handler classes, one for each sheet.
These handler classes implement `ExcelFixtureRowHandler`

[source,java]
----
public interface ExcelFixtureRowHandler {
    List<Object> handleRow(
            final FixtureScript.ExecutionContext executionContext,
            final ExcelFixture excelFixture,
            final Object previousRow);
}
----

The `handleRow` method is called for each row in the spreadsheet (of the appropriate sheet), and it is being responsible for handling the row of data from the spreadsheet.
A simple implementation would just use an injected repository to create a new entity.
A more sophisticated implementation would use the values in the spreadsheet to call other fixtures (using executionContext` and `excelFixture`).


== See also

* xref:testing:fixtures:about.adoc[] (in the xref:testing::about.adoc[Testing Guide]).
