How to count row table in JPA Query

Question

I'm new to Spring Boot. I have a mysql database, I use a query to count row in my table. But it's not work, it still return my original table data. Can you help me check my code.

Here is my Entity:

@Entity
@Table(name = "act_id_membership", schema = "activiti", catalog = "")
@IdClass(ActIdMembershipEntityPK.class)
public class ActIdMembershipEntity {
    private String userId;
    private String groupId;

    @Id
    @Column(name = "USER_ID_")
    public String getUserId() {
        return userId;
    }

    public void setUserId(String userId) {
        this.userId = userId;
    }

    @Id
    @Column(name = "GROUP_ID_")
    public String getGroupId() {
        return groupId;
    }

    public void setGroupId(String groupId) {
        this.groupId = groupId;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        ActIdMembershipEntity that = (ActIdMembershipEntity) o;
        return Objects.equals(userId, that.userId) &&
                Objects.equals(groupId, that.groupId);
    }

    @Override
    public int hashCode() {
        return Objects.hash(userId, groupId);
    }
}

Here is my query:

@Repository
public interface MemershipRepository extends JpaRepository<ActIdMembershipEntity, String> {
    @Query ("select new com.example.activiti_restful.dtos.UserMembership(i.userId, count(i)) from ActIdMembershipEntity i where i.userId ='kermit'")
    UserMembership countMemberships(String userId);
}

Updated code: My service class:

@Service
public class MembershipService {
@Autowired
private MemershipRepository repository;

public long count() {
    return repository.count();
}

My resource class:

@RestController
public class MembershipResource {
@Autowired
private MembershipService membershipService;

@GetMapping("/membership")
public long list() {return membershipService.count();}
}

My custom JSON Object class:

public class UserMembership {
    private String userId;

    private long numberOfusers;

    public UserMembership(String userId, long numberOfusers) {
        this.userId = userId;
        this.numberOfusers = numberOfusers;
    }
} 

MySQL Table: act_id_membership

Answer 1

According repositories documentation using CrudRepository provides a method called count() that is one of the Superinterfaces which JpaRepository is implemented.

Based CrudRepository documentation says:

long count(); Returns the number of entities.

Then you should use CrudRepository method. In addition Remove Uppercase MembershipREPOSITORY, by java code convention, you have to use by following way MembershipRepository.

 @Repository
 public interface MembershipRepository extends JpaRepository <ActIdMembershipEntity, String> {
 }

And use it in your Service:

 @Service
 public class MembershipService {

     @Autowired
     private MembershipRepository repo;

     public long count() {
         return repo.count();
     }
 }

UPDATED

Based on your requirement: In Controller:

@RestController
public class MembershipResource {

    @Autowired
    private MembershipService membershipService;

    @GetMapping("/membership")
    public List<Object> list() { return membershipService.countMemberships();
    }
}

In Service:

@Service
public class MembershipService {

    @Autowired
    private MemershipRepository repository;

    public List<Object> countMemberships() {
        return repository.countMemberships();
    }

}

In Repository:

@Repository
public interface MemershipRepository extends JpaRepository<ActIdMembershipEntity, String> {
    @Query ("select i.userId, count(i) from ActIdMembershipEntity i where i.userId ='kermit'")
    List<Object> countMemberships();
}