EclipseLink/Development/JPA2.0/Extended Map support

JPA 2.0 Map Support

Enhancement Request

Issue summary

Map support as defined in JPA 2.0 will require new mapping functionality for EclipseLink. The specification will allow any JPA 1.0 relationship mapping to be stored in a map with key being a primitive, an Embeddable or an Entity. For this support no user defined mapping or property exists on the target of the relationship as is the case in our current support. An additional complication is that the location of the Key fields exist on the relation table if one exists.

The Solution in General

Map behavior in EclipseLink is handled through ContainerPolicy. These mappings will be no different. a new subclass of MapContainerPolicy (MappedKeyMapContainerPolicy) will be added that is capable of reading and writing map keys that are stored in a database table, but not in the owning Entity, itself.

Use Cases

Both keys and values can be either of the following types: Basic, Embeddable, Entity. This results in the following types of maps.

Basic - Basic

• Both key and value are a basic
• Uses a CollectionTable
• CollectionTable contains foreign keys to the source, key and value
• This works like our BasicMapMapping

Basic - Embeddable

• Key is a basic, value is Embeddable
• Uses a CollectionTable
• CollectionTable contains - foreign keys to the source, key and all attributes of Embeddable
• This requires a MappedKeyMapContainerPolicy

Basic - Entity

• Key is a basic, value is Entity
• Several possible use cases
  • No Join Table (bidirectional OneToMany)
    • Key is a Mapped value in Target Entity
    • Value is the Target Entity
    • Target Entity maps join information
    • This is covered by our current MapKey Support
  • No Join Table (unidirectional OneToMany)
    • Same config as bidirectional OneToMany, but with new unidirectional OneToManySupport
  • Join Table with Key
    • Join table contains foreign keys for each side of the relationship and the key
    • Value is the target entity
    • This requires a MappedKeyMapContainerPolicy
  • Join Table with Key on Target
    • Join table contains foreign keys for each side of the relationship
    • Value is the target entity
    • Key is a mapped value of on the target entity
    • Our current MapKey support covers this case

Embeddable - Basic

• Key is Embeddable, value is Basic
• Uses a Collection Table
• CollectionTable contains foreign keys to the source, all the fields of the embeddable and the value
• This requires a MappedKeyMapContainerPolicy

Embeddable - Embeddable

• Key is Embeddable, value is Embeddable
• Uses a Collection Table
• Collection Table contains a forein key, all the fields of both embeddables (note: if key and value map to the same columns through overrides then the table will only contain one set of information about the embeddable)
• This requires a MappedKeyMapContainerPolicy

Embeddable - Entity

• Key is Embdeddable, value is Entity
• Several Possible use cases
  • No Join Table (bidirectional OneToMany)
    • Key is a Embedded within the Entity
    • Value is the Entity itself
    • Target Entity Maps Join information
    • Covered by our current MapKey Support
  • No Join Table (unidirectional OneToMany)
    • Same config as bidirectional OneToMany, but with new unidirectional OneToManySupport
  • Join Table with Key
    • Join table contains foreign keys for each Entity and fields of Embeddable
    • Value is the target entity
    • This requires a MappedKeyMapContainerPolicy
  • Join Table no key
    • Join table contains foreign keys for each Entity
    • Key is Embedded in target Entity
    • Value is target Entity
    • Our Current MapKey support covers this case

Entity - Basic

• Key is Entity, value is Basic
• Uses a Collection Table
• Collection table contains foreign keys to the source, foreign keys to the key and the value
• This requires a MappedKeyMapContainerPolicy

Entity - Embeddable

• Key is Entity, value is Embeddable
• Uses a Colleciton Table
• Collection table contains foreign keys to the source, foreign keys to the key and all the values of the embedded value
• This requires a MappedKeyMapContainerPolicy

Entity - Entity

• Key is Entity, value is Entity
• Two use cases
  • Join Table
    • Uses a Join table
    • Join table contains foreign keys to the source, foreign keys to the key and foreign keys to the value
    • This requires a MappedKeyMapContainerPolicy
  • No Join Table
    • Target table contains Foreign keys to source, inforamtion about target and Foreign keys to Key
    • Support required or UniDirectional OneToMany and Bidirectional OneToMany
    • This requires a MappedKeyMapContainerPolicy

Design

• MappedKeyMapContainerPolicy

Archived Initial Design

The following contains information about the initial design proposal. It has now been modified.

The Solution in General

The general approach to implementing this functionality will be to produce Map mappings that encapsulate two EclipseLink mappings. A generated mapping that represents the Key attribute and a user defined mapping that represents the value of the map. It is expected that two Map Mappings will be needed. A Mapping where the Key mapping columns are found in the target table and another where the Key mapping columns are found in the relation table (CollectionTableMapMapping).

The Details

Target Table Map Mapping

Enhancement Request

This support will cover the case where the Map key columns exist in the target table

EclipseLink Mappings Involved

- AggregateCollectionMapping

- Bi-directional OneToMany

- New Uni-directional OneToMany mapping

JPA Mappings

- Bi-directional OneToMany mapping

- Uni-directional OneToMany with @JoinColum

- ElementCollection<*, Primitive> mapping

- ElementCollection<*, Embeddable> mapping

Join Table Map Mapping (or CollectionTableMapMapping)

Enhancement Request

This support will cover the case where the Map key columns exist in the Join table

EclipseLink Mappings Involved

- ManyToMany mapping

JPA Mappings

- default Uni-directional OneToMany with @JoinColum

- ManyToMany mapping

- Note: The specification disallows both sides of a mapping using a Map collection but there is no technical reason to do this as one side will be read-only anyway.