DbForeignKey (ebean-annotation 6.15 API)

```
@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
```
{@code
```

Optional Element Summary

Optional Elements
Modifier and Type	Optional Element	Description
`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 Detail
  - onDelete
```
ConstraintMode onDelete
```
    Specify the onDelete mode. Typically will default to RESTRICT (aka No Action).
    
    Default:
    
    io.ebean.annotation.ConstraintMode.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:
    
    io.ebean.annotation.ConstraintMode.RESTRICT
- - noConstraint
```
boolean noConstraint
```
    Set to true when we do not wish any foreign key constraint to be created. When this is set to true the onDelete and onUpdate have no effect.
    
    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