Relationships between database entities or Java objects are necessary for most applications. The Guestbook application, therefore, defines a relationship between a Guestbook and its entries.
As mentioned earlier, each entry must belong to a particular Guestbook.
Therefore, each GuestbookEntry
entity must relate to a Guestbook
entity.
Create the GuestbookEntry
entity’s fields:
<entity name="GuestbookEntry" local-service="true" uuid="true" remote-service="true">
<column name="entryId" primary="true" type="long" />
<column name="name" type="String" />
<column name="email" type="String" />
<column name="message" type="String" />
<column name="guestbookId" type="long" />
Note the last field in the list is the guestbookId
field. Since it’s the same
name as the Guestbook
object’s primary key, a relationship is created between
the two objects. If you’re using Liferay Dev Studio DXP, you can see this relationship in
its diagram mode.
Figure 1: Relating entities is a snap in Liferay Dev Studio DXP's *Diagram* mode for `service.xml`.
Congratulations! You’ve related two entities.
Next, add the instance, audit, and status fields mentioned from the previous step to enable Liferay’s multi-tenancy, audit, and workflow features.
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.