Spring mvc : Saving a Java List in PostgreSQL with Hibernate

Question

I am working on a Spring-MVC project where I am using Hibernate for persistence. In one of the model classes I have a List which I want to persist. I am facing the problem as I don't know which dataType to use in PostgreSQL and do I need instruct hibernate in some way or other that I am trying to persist a List. Performance requirements are not that much of a problem on this list, as it does not get that much action. I am posting some code for reference, kindly let me know. Thanks a lot :

GroupAccount model class :

@Entity
@Table(name="groupaccount")
public class GroupAccount {
 @Column(name = "blacklist")
 private List<String> blacklist;
 public List<String> getBlacklist() {
 return blacklist;
 }
 public void setBlacklist(List<String> blacklist) {
 this.blacklist = blacklist;
 }
}

I would sometimes require to update the values of the blacklist, so I have a method in DAO which updates the groupAccount, I am pasting it below.

GroupAccountDAOImpl edit function :

 @Override
 public void editGroupAccount(GroupAccount groupAccount) {
 session = this.sessionFactory.getCurrentSession();
 GroupAccount groupAccount1 = (GroupAccount)session.get(GroupAccount.class,groupAccount.getGroupId());
 if(!(groupAccount1==null)){
 groupAccount.setOwnedcanvas(groupAccount1.getOwnedcanvas());
 groupAccount.setGroupMembersSet(groupAccount1.getGroupMembersSet());
 session.merge(groupAccount);
 session.flush();
 }
 }

One use-case for adding users in blacklist :

List<String> blackListUsers;
blackListUsers = groupAccount.getBlacklist();
blackListUsers.add(memberForBlackListing.getMemberUsername());
groupAccount.setBlacklist(blackListUsers);
this.groupAccountService.editGroupAccount(groupAccount);
removeAllMemberships(memberId);
return true;

Any help would be nice. Thanks a lot. :-)

Answer 1

You can't map List<String> to a single column. For these cases, @ElementCollection is used

@ElementCollection
@CollectionTable(name="blacklist", joinColumns=@JoinColumn(name="group_account_id")
@Column(name = "name")
private List<String> blacklist;

This requires a database table named blacklist with columns name and group_account_id (which will be used as a foreign key to group_account table). Of course, table and column names are customizable.

• We are Borg: Ok. Thanks a lot, but is there some other type I can use, like an array which I can use for the above mentioned use-case. I just need to check if an email-address exists in the blacklist and add an Email, but in same database table. Thanks a lot.
• Predrag Maric: You can use simple String field, and keep the list as comma separated values (CSV). Requires a little pack-unpack code, but it's the simplest solution.
• We are Borg: I agree. I will try with that. Thanks a lot.