Defining a Custom Finder Method

Dynamic queries belong in finder methods. You implement them and then make them available through an interface. This tutorial demonstrates defining the finder method in an implementation class, generating its interface and tying the implementation to the interface.

An example of this is a Guestbook application with two entities: guestbook and entry. Each entry belongs to a guestbook so the entry entity has a guestbookId field as a foreign key. If you need a finder to search for guestbook entries by entry name and guestbook name, you’d add a finder method to GuestbookFinderImpl and name it findByEntryNameGuestbookName. The full method signature would be findByEntryNameGuestbookName(String entryName, String guestbookName). The steps are below.

1. Create a [Entity]FinderImpl class in the [package path].service.persistence.impl package of your service module’s src/main/java folder. Recall that you specify the [package path] in your service.xml file. Here’s an example:

   <service-builder package-path="com.liferay.docs.guestbook">
       ...
   </service-builder>
   

2. Define a findBy* finder method in the class you created. Make sure to add any required arguments to your finder method signature.

3. Run Service Builder to generate the appropriate interface in the [package path].service.persistence package in the service folder of your API and service modules.

   For example, after adding findByEntryNameGuestbookName(String entryName, String guestbookName) to GuestbookFinderImpl and running Service Builder, the interface com.liferay.docs.guestbook.service.persistence.GuestbookFinder is generated.

4. Make the finder class a component (annotated with @Component) that implements the finder interface. For example, the class declaration should look like this:

   @Component(service = GuestbookFinder.class)
   public class GuestbookFinderImpl extends BasePersistenceImpl<Guestbook> implements GuestbookFinder
   

Your next step is to implement the query in your finder method using the Dynamic Query API.