Defining Relationships Between Service Entities

Referencing one type of entity in the context of another entity is a common requirement. This is also known as relating entities. Liferay’s Bookmarks application defines a relationship between an entry and its folder.

As mentioned earlier, each bookmark must have a folder. Therefore, each BookmarksEntry entity must relate to a BookmarksFolder entity. Liferay Dev Studio DXP’s Diagram mode for service.xml facilitates relating entities.

  1. Select Diagram mode for the service.xml file.

  2. Select the Relationship option under Connections in the palette on the right side of the view. This relationship tool helps you draw relationships between entities in the diagram.

  3. Click your first entity and move your cursor over to the entity you’d like to relate it with. Liferay Dev Studio DXP draws a dashed line from your selected entity to the cursor.

  4. Click the second entity to complete drawing the relationship. Liferay Dev Studio DXP turns the dashed line into a solid line, with an arrow pointing to the second entity.

  5. Save the service.xml file.

Congratulations! You’ve related two entities. Their relationship shows in Diagram mode and looks similar to the relationship in the figure below.

Figure 1: Relating entities is a snap in Liferay Dev Studio DXPs Diagram mode for service.xml.

Figure 1: Relating entities is a snap in Liferay Dev Studio DXP's *Diagram* mode for `service.xml`.

Switch to Source mode in the editor for your service.xml file and note that Liferay Dev Studio DXP created a column element in the first selected entity to hold the ID of the corresponding entity instance reference. For example, the BookmarksEntry entity uses this column to relate to a BookmarksFolder entity :

<column name="folderId" type="long" />

Now that your entity columns are in place and entity relationships are established, you can specify the default order in which the entity instances are retrieved from the database.

« Defining the Columns (Attributes) for Each Service EntityDefining Ordering of Service Entity Instances »
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