= Tabular Extension

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The Tabular Extension module integrates with the xref:vw:ROOT:about.adoc[Wicket Viewer] to allow any collection to be downloaded as specific tabular data file (e.g. an Excel spreadsheet).

The viewer automatically makes the "download" menu item available for all tables:

image::screenshot.png[width=300px]

== 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-tabular</artifactId>
            <scope>import</scope>
            <type>pom</type>
            <version>{page-causewayreleaseversion}</version>
        </dependency>
    </dependencies>
</dependencyManagement>
----

=== Dependencies / Imports

In the webapp module of your application, add the following dependency:

[source,xml]
.pom.xml
----
<dependency>
    <groupId>org.apache.causeway.extensions</groupId>
    <artifactId>causeway-extensions-tabular-excel</artifactId>
</dependency>
----

In your application's xref:userguide::modules.adoc#appmanifest[App Manifest], import the extension's implementation module:

[source,java]
.AppManifest.java
----
@Configuration
@Import({
        CausewayModuleExtTabularExcel.class,
        ...
})
public class AppManifest {
}
----

== Custom Export (SPI)

To provide a custom exporter, simply implement `TabularExporter` and register with _Spring_.

[source, java]
.Tabular Exporter (SPI)
----
package org.apache.causeway.applib.tabular;

/**
 * SPI to provide file export to table views.
 *
 * @since 3.2
 */
public interface TabularExporter {

    /**
     * Implementing exporters need to write given tabular data from
     * {@link org.apache.causeway.commons.tabular.TabularModel.TabularSheet} into the {@link File exportFile},
     * which is provided by the framework for the duration of a single request cycle.
     *
     * @param dataTable data model for the table
     * @param exportFile destination, this exporter writes its data to
     */
    void export(TabularModel.TabularSheet tabularSheet, File exportFile);

    CommonMimeType getMimeType();

    /**
     * @return label for the "View as" dropdown for "collection contents as"
     * component factories
     */
    String getTitleLabel();

    /**
     * @return CSS class for the icon/image next to "View as" dropdown
     * for "collection contents as" component factories
     */
    String getCssClass();

    /**
     * An ordinal, that governs the order of appearance in the UI dropdown.
     * <ul>
     * <li>{@literal 1000..1999} reserved for different table presentations</li>
     * <li>{@literal 2000..2999} reserved for different table exports</li>
     * </ul>
     * <p>
     * Lowest comes first.
     */
    int orderOfAppearanceInUiDropdown();

    /**
     * Whether this exporter applies to given {@code elementType}.
     * If <code>false</code>, this exporter is not provided to end users.
     */
    default boolean appliesTo(final Class<?> elementType) { return true; }

    /**
     * Writes given tabular data to a {@link Blob}, using given sheet's name as blob name.
     */
    @SneakyThrows
    default Blob exportToBlob(final TabularModel.TabularSheet tabularSheet) {
        var tempFile = File.createTempFile(this.getClass().getCanonicalName(), tabularSheet.sheetName());
        try {
            export(tabularSheet, tempFile);
            return Blob.of(tabularSheet.sheetName(), getMimeType(), DataSource.ofFile(tempFile).bytes());
        } finally {
            Files.deleteIfExists(tempFile.toPath()); // cleanup
        }
    }

}

----

== Tabular Model

Underneath a general purpose tabular model is used, with simple buildings blocks

* Cell
* Column
* Row
* Sheet

[source, java]
.Tabular Model Example
----
import org.apache.causeway.commons.tabular.*;
import org.apache.causeway.commons.collections.Can;

// create a TabularModel with 2 columns and 2 rows ..  
        
var col1 = new TabularModel.TabularColumn(0, "Col-1", "Column Description 1");
var col2 = new TabularModel.TabularColumn(1, "Col-2", "Column Description 2");

var row1 = new TabularModel.TabularRow(Can.of(
        TabularModel.TabularCell.single("cell1-1"), 
        TabularModel.TabularCell.single("cell1-2")));
var row2 = new TabularModel.TabularRow(Can.of(
        TabularModel.TabularCell.single("cell1-1"), 
        TabularModel.TabularCell.single("cell1-2")));

var sheet = new TabularModel.TabularSheet("sheet-1", Can.of(col1, col2), Can.of(row1, row2));

var tabularModel = new TabularModel(sheet);
----
