MapKey

```
@Target({METHOD,FIELD})
@Retention(RUNTIME)
public @interface MapKey
```
Specifies the map key for associations of type Map when the map key is itself the primary key or a persistent field or property of the entity that is the value of the map.
If a persistent field or property other than the primary key is used as a map key then it is expected to have a uniqueness constraint associated with it.
The MapKeyClass annotation is not used when MapKey is specified and vice versa.
Example 1: {@snippet :

Since:

1.0

Optional Element Summary

Optional Elements
Modifier and Type	Optional Element	Description
`java.lang.String`	`name`	(Optional) The name of the persistent field or property of the associated entity that is used as the map key.

- Element Detail
  - name
```
java.lang.String name
```
    (Optional) The name of the persistent field or property of the associated entity that is used as the map key.
    Default: If the name element is not specified, the primary key of the associated entity is used as the map key. If the primary key is a composite primary key and is mapped as IdClass, an instance of the primary key class is used as the key.
    
    Default:
    
    ""