How to Reference a Column Other Than 'Id' for a Joincolumn

Is it possible to reference a column other than 'id' for a JoinColumn?

I think Doctrine wants these to be primary keys, from the docs:

name: Column name that holds the foreign key identifier for this relation.

Another thing that jumps out at me from your code sample is category.id2 being type string, I would at least expect it to be an integer, but it may also need to be for @JoinColumn to work properly.

You may be able to get away with just @Index on category.id2 and leave it as a string though; worth a shot anyway.

Join column from another table with Foreign Key using JPA

I don't really understand this. I'm sure @JoinColumn can accomplish the behavior you're looking for.

I was looking into @JoinColumn but was not seeing the result I wanted since the foreign key is a different column in my Entity

Example:

@Entity
@Table(name = "jobs")
public class KronosFileEntity {

    @Id
    @Column(name = "id")
    private Long id;

    @ManyToOne
    @JoinColumn(name = "user_id", referencedColumn = "id")
    private User user;
}

Then you can access the email like job.getUser().getEmail()
Or add a convenience method if that helps

public String getUserEmail() {
   return user.getEmail();
}

Then
job.getUserEmail()

Join columns by referencedColumnName that is not primary key - id

You have mixed up the column-name and the field-name that shall be referenced in your @JoinColumn declaration.

@JoinColumn(name="id", referencedColumnName="user_id")

This way Doctrine looks for a field/property named user_id on your User entity. I guess you want the column in the join-table to be named user_id and the entries being id's of the User entity.

UserDetail

/**
 * @ORM\Entity
 */
class UserDetail
{
    /**
     * @ORM\ManyToOne(
     *   targetEntity="User",
     *   inversedBy="details"
     * )
     * @ORM\JoinColumn(
     *   name="user_id",
     *   referencedColumnName="id"
     * )
     */
    protected $user;

    public function setUser(User $user)
    { 
        $this->user = $user;

        return $this;
    }

    /** @ORM\Column() */
    protected $key;

    /** @ORM\Column() */
    protected $value;

    public function __construct($key, $value)
    {
       $this->key = $key;
       $this->value = $value;
    }

User

class User
{
    /**
     * @ORM\Id()
     * @ORM\Column(type="integer")
     */
    protected $id;

    /** 
     * @ORM\OneToMany(
     *   targetEntity="UserDetail",
     *   mappedBy="user", 
     *   cascade={
     *     "persist",
     *     "remove",
     *     "merge"
     *   },
     *   orphanRemoval=true
     * )
     */
    protected $details;

    public function __construct()
    {
        $this->details = new ArrayCollection();
    }

    public function addDetail(UserDetail $detail)
    {
        $detail->setUser($this);
        $this->details->add($detail);

        return $this;
    }

Now if you add a detail to your User like this and persist/flush afterwards:

$user->addDetail(new UserDetail('Height', '173cm'));

This will result in a join-colum in the user_detail table that looks like this:

| key           | value     | user_id |
|---------------|-----------|---------|
| Height        | 173cm     | 1       |

JPA : relation with other column than id

Use the referencedColumnName attribute of the @JoinColumn annotation. I'm not sure this is supported by the standard though. It might work in some implementations, and not in others.

See http://docs.jboss.org/hibernate/stable/annotations/reference/en/html/entity.html#entity-mapping-association for Hibernate, and http://openjpa.apache.org/builds/2.1.0/apache-openjpa-2.1.0/docs/manual/manual.html#ref_guide_mapping_notes_nonstdjoins for OpenJPA.

Hibernate select id of join column without join

You can map the foreign key to the entity twice in this case, one for actual ORM and another for getting the FK without actually firing a new query.

public class Answer {
   @JoinColumn(name = "question_id")
   @ManyToOne(targetEntity = Question.class, fetch = FetchType.LAZY)
   private Question question;

   @Column(name = "question_id", insertable = false, updatable = false)
   private Long questionId;
}

Here question_id is present in the answer table.

This way that foreign key will be already available in the result of the first query(in the questionId field) and the new query won't be fired for getting the FK value.

What is referencedColumnName used for in JPA?

It is there to specify another column as the default id column of the other table, e.g. consider the following

TableA
  id int identity
  tableb_key varchar

TableB
  id int identity
  key varchar unique

// in class for TableA
@JoinColumn(name="tableb_key", referencedColumnName="key")

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