How to count row table in JPA Query - mysql

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();
}

Answer 2

*> Actually I want it return a json format like [{ name: kermit, value:6}]. Now it just return a number 6 only. How I can do that? Thank you!
First, create a class to wrap your data:
public class UserMembership {
private String userId;
private long numberOfUsers;
public UserMembership(String userId, long numberOfUsers) {
this.userId = userId;
this.numerOfUsers = numberOfUsers;
}
}
Then
#Repository
public interface MembershipRepository extends JpaRepository <ActIdMembershipEntity, String> {
#Query ("select new *****.UserMembership(i.userId, count(i)) from ActIdMembershipEntity i where i.userId = :userId")
UserMembership countMemberships(String userId);
}
*****: your full package name
Hope it help!