Play framework FORM binding to Set instead of List

Is there any way to properly bind to a Set on a form?

I'm doing POJO binding and my controller takes in a User object

public static void create(User user)

user.java

public class User implements Serializable {



    public Long id;

    @Required
    @Email
    public String email;

    public Set<Group> groups;

}

Group.java

    public class Group implements Serializable {

        public Long id;

        public String name;

    }

I can't seem to get my field to bind to groups

i've tried user.groups[].id, user.groups[0].id, user.groups.id. I can get it to work with 开发者_Python百科a list just fine but when it posts I get a list of N elements with a bunch of null items (one null for each checkbox that was not checked) and I could just create a new list without the nulls but that seems wrong.

Edit: User and Group are not meant to be persistent entities, Play is merely acting as a stateless and persistent-less presentation layer for a restful API

---

The new Binder implementation of Play 1.2.4 allows this.

In Play versions earlier to 1.2.4 (released December 02, 2011) you could not bind a set by sending parameters like

user.groups[1].id = 1
user.groups[1].name = "name1"
user.groups[3].id = 3
user.groups[3].name = "name3"
user.groups[4].id = 4
user.groups[4].name = "name4"

The problem with binding to a List is that you will get a List of length 5 where the value at 0 and 2 is null.

If you still need to use Play version minor than 1.2.4, a workaround for this problem could be using

Map<String, Group> groups

instead of Set or List. Then you won't get null elements in between and you will get Collection by calling groups.values().

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First, since User and Group seems to be Entity, you should extend the play.db.jpa.Model class and also define it as an @Entity. For example:

@Entity
public class User extends Model {

    ...

}

Thanks to the extension of Model, you do not need to define the technical ID (i.e. you can remove the public Long id), and you will have a generic DAO for this class (see the Javadoc)

Now, you have to define the groups of User like that:

@ManyToMany
public Set<Group> groups;

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I have similiar issue with Play. Play's binding is auto-magic, but sometimes you need to have to workarounds.

You can simply create a setter

public void setGroups(List<Group> groups)

And internally set the provided groups to your set. It is a bit dirty but will work.

I also recommend you to create a Unit test case to simulate the binding. Create a Map to simulate POST request and bind the map to your object to the Binder. It is much easier than repeating the process from web-interface, and it forms a regression test and alert you if Play's update break some of the binding behaviors (it happens to me).