Module io.ebean.annotation
Package io.ebean.annotation

Annotation Type DbForeignKey

@Retention(RUNTIME) @Target(FIELD) public @interface DbForeignKey
Specify how a foreign key constraint should be defined.

We can specify if a constraint should not be defined at all or control the onDelete and onUpdate modes used.

Example: On delete cascade



 @DbForeignKey(onDelete = ConstraintMode.CASCADE)
 @ManyToOne
 RelatedBean parent;

Example: No foreign key



 // No FK Constraint
 @DbForeignKey(noConstraint=true)
 @ManyToOne
 RelatedBean parent;

Example: On delete set null



 @DbForeignKey(onDelete = ConstraintMode.SET_NULL)
 @ManyToOne
 RelatedBean parent;

Example: Allow inconsistency:


 // disable foreign keys and force ebean to use left joins
 @DbForeignKey(noConstraint=true, forceLeftJoin=true)
 // the reference column in the database will be NOT NULL
 @ManyToOne(optional=false)
 RelatedBean parent;
To create such a bean, 'parent' must not be null (because of 'optional=false'). There is no FK constraint, that enforces that 'parent' exists, so you can even use a non existent (or not yet existent) reference bean with a particular ID and create. that bean in a later step.

Ebean will also be enforced to use LEFT JOINs instead of INNER JOINS, so that the query result wouldn't skip entries if a non-existent relation is involved.
Note: In this case, the 'parent' may not be null, but you'll get an EntityNotFoundException when accessing properties of 'parent'

  • Optional Element Summary

    Optional Elements
    Modifier and Type
    Optional Element
    Description
    boolean
    forceLeftJoin
    If this is set to true, LEFT JOIN is always used in queries, because data may be inconsistent and we cannot rely to have matching join partners.
    boolean
    noConstraint
    Set to true when we do not wish any foreign key constraint to be created.
    boolean
    noIndex
    Set to true when we do not wish an index to be created on the foreign key column(s).
    ConstraintMode
    onDelete
    Specify the onDelete mode.
    ConstraintMode
    onUpdate
    Do NOT change this - seriously, don't do it.

  • Element Details

    • onDelete

      ConstraintMode onDelete
      Specify the onDelete mode. Typically will default to RESTRICT (aka No Action).
      Default:
      RESTRICT

    • onUpdate

      ConstraintMode onUpdate
      Do NOT change this - seriously, don't do it.

      Your primary keys should never change by design. We should orientate the design to support primary keys that change (and instead find better non mutating primary keys). Oracle go to the point of actively not supporting "on update" for this reason.

      So yes, we can specify the onUpdate mode but I don't expect anyone to change this.

      Default:
      RESTRICT

    • noConstraint

      boolean noConstraint
      Set to true when we do not wish any foreign key constraint to be created. (either for performance reasons, or data may be inconsistent) When this is set to true the onDelete and onUpdate have no effect.

      Note: This setting controls only ddl-generation. By default, we still assume, that the data is consistent and we may use INNER JOINs.

      Default:
      false

    • forceLeftJoin

      boolean forceLeftJoin
      If this is set to true, LEFT JOIN is always used in queries, because data may be inconsistent and we cannot rely to have matching join partners.

      Note: This setting controls only sql-generation (left join vs. join). You may need noConstraint = true in most cases.

      Default:
      false

    • noIndex

      boolean noIndex
      Set to true when we do not wish an index to be created on the foreign key column(s).
      Default:
      false