I am working on a Spring-MVC application where I have a many-to-many relationship in which I have to query in 2 tables to get the values I require. I will explain in more detail.
This is what I am looking for :
Below is the SQL code and Spring-mvc code to understand more better.
CREATE TABLE public.groupaccount (
groupid NUMERIC NOT NULL,
groupname VARCHAR,
groupaccountstatus BOOLEAN DEFAULT false NOT NULL,
adminusername VARCHAR,
CONSTRAINT groupid PRIMARY KEY (groupid)
);
CREATE TABLE public.groupmembers (
memberid INTEGER NOT NULL,
musername VARCHAR
CONSTRAINT memberid PRIMARY KEY (memberid)
);
CREATE TABLE public.memberjunction (
memberid INTEGER NOT NULL,
groupid NUMERIC NOT NULL,
CONSTRAINT membergroupid PRIMARY KEY (memberid, groupid)
);
GroupMembersDAOImpl :#
@Override
public List<Integer> returnMemberIdWithMatchingUsername(String memberUsername) {
session = this.sessionFactory.getCurrentSession();
org.hibernate.Query query = session.createQuery("From GroupMembers as " +
"n where n.memberUsername=:memberUsername");
query.setParameter("memberUsername",memberUsername);
List<GroupMembers> memberList = query.list();
List<Integer> memberIdList = new ArrayList<>();
for(GroupMembers members :memberList){
memberIdList.add(members.getMemberid());
}
return memberIdList;
}
GroupAccount model :
@Entity
@Table(name="groupaccount")
public class GroupAccount {
@Id
@Column(name="groupid")
@GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "groupaccount_seq_gen")
@SequenceGenerator(name = "groupaccount_seq_gen",sequenceName = "groupaccount_seq")
private Long groupId;
@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "memberjunction", joinColumns = {@JoinColumn(name = "groupid")},
inverseJoinColumns = {@JoinColumn(name = "memberid")})
private Set<GroupMembers> groupMembersSet = new HashSet<>();
public void setGroupMembersSet(Set<GroupMembers> groupMembersSet){
this.groupMembersSet = groupMembersSet;
}
}
GroupMembers model class :
@Entity
@Table(name="groupmembers")
public class GroupMembers {
@Id
@Column(name="memberid")
@GeneratedValue(strategy = GenerationType.SEQUENCE,generator = "groupmembers_seq_gen")
@SequenceGenerator(name = "groupmembers_seq_gen",sequenceName = "groupmembers_seq")
private int memberid;
@ManyToMany(mappedBy = "groupMembersSet")
private Set<GroupAccount> groupAccounts = new HashSet<>();
public void setGroupAccounts(Set<GroupAccount> groupAccounts){
this.groupAccounts = groupAccounts;
}
public Set<GroupAccount> getGroupAccounts(){
return this.groupAccounts;
}
}
Query I am using :
@Override
public int getMemberIdForCanvas(String memberUsername, Long groupId) {
session = this.sessionFactory.getCurrentSession();
org.hibernate.Query query = session.createQuery("select distinct m.memberId from GroupMembers m\n" +
"join m.groupAccounts a\n" +
"where a.memberUsername = :userName and m.groupId=:groupId");
query.setParameter(memberUsername,"memberUsername");
query.setParameter(String.valueOf(groupId),"groupId");
int memberid = (Integer)query.uniqueResult();
return memberid;
}
Any help would be nice. Thanks a lot.
Here's the documentation for joins and HQL . Please read it.
The query is as simple as
select distinct m.memberId from GroupMembers m
join m.groupAccounts a
where a.memberUsername = :userName
Please also fix your naming. A GroupMembers
instance is a single group member. So the class should be named GroupMember
, without s
. Repeating the name of the class in the fields of this class is also redundant: member.getId()
is more readable and less verbose than member.getMemberId()
. Same for the other fields.
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