Latest revision as of 16:01, 3 April 2009

JPA 2.0 Map Support

JPA 2.0 Root | 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.

x - Basic

• The mappings: BasicCollectionMapping is used

Basic - Basic/Embeddable

• Both key and value are a basic
• Target table is same for key and for the value
• CollectionTable contains foreign keys to the source, key and the value
• This is BasicMapMapping
• Can also be supported with a BasicCollectionMapping with a MappedKeyMapContainerPolicy containing a DirectToFieldMapping

Annotation example - Basic key

@ElementCollection
@MapKeyColumn(name="Q_DATE")
@MapKeyTemporal(DATE)
@Column(name="QUOTE")
@CollectionTable(
    name="EXPERT_QUOTES",
    joinColumns=@JoinColumn(name="EBC_ID"))
public Map<Date, String> getQuotes() {
    return quotes;
}

XML example - Basic key

<element-collection name="quotes">
    <map-key-temporal>DATE</map-key-temporal>
    <map-key-column name="Q_DATE"/>
    <column name="QUOTE"/>
    <collection-table name="EBC_QUOTES">
        <join-column name="EBC_ID"/>
    </collection-table>
</element-collection>

Embeddable - Basic

• Key is Embeddable, value is Basic
• Information about the key and the value are both stored in the target table
• CollectionTable contains foreign keys to the source, all the fields of the embeddable and the value
• BasicCollectionMapping with MappedKeyMapContainerPolicy containing an AggregateObjectMapping

Annotation example

@ElementCollection(fetch=EAGER)
@MapKeyClass(Birthday.class)
@AttributeOverrides({
    @AttributeOverride(name="key.day", column=@Column(name="BIRTH_DAY")),
    @AttributeOverride(name="key.month", column=@Column(name="BIRTH_MONTH")),
    @AttributeOverride(name="key.year", column=@Column(name="BIRTH_YEAR"))
})
@Column(name="DETAILS")
@CollectionTable(
    name="EXPERT_CELEBRATIONS",
    joinColumns=@JoinColumn(name="EBC_ID"))
public Map<Birthday, String> getCelebrations() {
    return celebrations;
}

XML example

<element-collection name="celebrations" fetch="EAGER">
    <map-key-class class="Birthday"/>
    <map-key-attribute-override name="day">
        <column name="BIRTH_DAY"/>
    </map-key-attribute-override>
    <map-key-attribute-override name="month">
        <column name="BIRTH_MONTH"/>
    </map-key-attribute-override>
    <map-key-attribute-override name="year">
        <column name="BIRTH_YEAR"/>
    </map-key-attribute-override>
    <column name="DETAILS"/>
    <collection-table name="EXPERT_CELEBRATIONS">
        <join-column name="EBC_ID"/>            
     </collection-table>    
</element-collection>  

Entity - Basic

• Key is Entity, value is Basic
• target table contains foreign keys to the source, foreign keys to the key and the value
• BasicCollectionMapping with MappedKeyMapContainerPolicy containing a OneToOneMapping

x - Embeddable

• AggregateCollectionMapping is used

Basic - Embeddable

• Key is a basic, value is Embeddable
• target table contains - foreign keys to the source, key and all attributes of Embeddable
• AggregateCollectionMapping with MappedKeyMapContainerPolicy containing a DirectToFieldMapping

Annotation example

Here the type T is a generic type defined by a sub entity.

@Entity
@Table(name="CMP3_CONSUMER")
@Inheritance(strategy=JOINED)
@DiscriminatorValue(value="BC")
public class BeerConsumer<T>

....

    @ElementCollection
    // Map key class will get figured out through generic types.
    @MapKeyColumn(name="RS_KEY")
    @CollectionTable(name="CONSUMER_REDSTRIPES", joinColumns=@JoinColumn(name="C_ID", referencedColumnName="ID"))
    public Map<T, RedStripe> getRedStripes() {
        return redStripeBeersToConsume;
    }

....

XML example - TBD

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)
• AggregateCollectionMapping with MappedKeyMapContainerPolicy containing an AggregateObjectMapping

Entity - Embeddable

• Key is Entity, value is Embeddable
• target table contains foreign keys to the source, foreign keys to the key and all the values of the embedded value
• AggregateCollectionMapping with MappedKeyMapContainerPolicy containing a OneToOneMapping

x - Entity

• The majority of the cases occur when the target is an Entity
• The mappings: OneToMany, UnidirectionalOneToMany and ManyToMany are potentially used

Basic/Embeddable - Entity

• Key is a basic or embeddable, and value is an entity
• Several possible use cases
  • Key is a mapped value in target object
    • Covered by our current MapKey support
    • OneToMany, UnidirectionalOneToMany and ManyToMany
  • Key is stored in target table, but not mapped in target object
    • target table contains values needed to build the target and values needed to build the key
    • OneToManyMapping or UnidirectionalOneToManyMapping with MappedKeyMapContainerPolicy containing a DirectToFieldMapping or AggregateObjectMapping
  • Key is stored in collection table
    • collection table contains foreign keys to the source, foreign keys to the value, and all fields need to build the key
    • ManyToManyMapping with MappedKeyMapContainerPolicy containing a DirectToFieldMapping or AggregateObjectMapping

Annotation example - Embeddable key

@OneToMany(mappedBy="beerConsumer", cascade=ALL)
// MapKeyClass picked up from the generic type
@AttributeOverride(name="number", column=@Column(name="TAG_NUMBER"))
public Map<CoronaTag, Corona> getCoronaBeersToConsume() {
    return coronaBeersToConsume;
}

Annotation example - Basic key

@OneToMany(mappedBy="beerConsumer", cascade=ALL, fetch=EAGER)
@MapKeyColumn(name="BOTTLED_DATE")
@MapKeyTemporal(DATE)
public Map<Date, Heineken> getHeinekenBeersToConsume() {
    return heinekenBeersToConsume;
}

XML example - Embeddable key

<one-to-many name="coronaBeersToConsume" mapped-by="beerConsumer" target-entity="Corona">
    <!-- map key class picked up from the generic type -->
    <map-key-attribute-override name="number">
        <column name="TAG_NUMBER"/>
    </map-key-attribute-override>
    <cascade>
          <cascade-all/>
    </cascade>
</one-to-many>

XML example - Basic key

<one-to-many name="heinekenBeersToConsume" mapped-by="beerConsumer" target-entity="Heineken">
    <map-key-temporal>DATE</map-key-temporal>
    <map-key-column name="BOTTLED_DATE"/>
    <cascade>
        <cascade-all/>
    </cascade>
</one-to-many>

Entity - Entity

• Key is an Entity, Value is an Entity
• Several possible use cases
  • Key is a mapped value in target object
    • Covered by our current MapKey support
    • OneToMany, UnidirectionalOneToMany and ManyToMany
  • Key is referenced from target table but not mapped in target object
    • target table contains values need to build the target, and foreign keys to the key
    • OneToManyMapping or UnidirectionalOneToManyMapping with MappedKeyMapContainerPolicy containing a OneToOneMapping
  • Key is referenced from the collection table
    • collection table contains foreign keys to the source, foreign keys to the value, and foreign keys to the key
    • ManyToManyMapping with MappedKeyMapContainerPolicy containing a OneToOneMapping

Annotation example

@OneToMany(targetEntity=Becks.class, mappedBy="beerConsumer", cascade=ALL)
@MapKeyClass(BecksTag.class)
@MapKeyJoinColumn(name="TAG_ID", referencedColumnName="ID")
public Map getBecksBeersToConsume() {
    return becksBeersToConsume;
}

XML example

<one-to-many name="becksBeersToConsume" mapped-by="beerConsumer" target-entity="Becks">
    <map-key-class class="BecksTag"/>
    <map-key-join-column name="TAG_ID" referenced-column-name="ID"/>
    <cascade>
        <cascade-all/>
    </cascade>
</one-to-many>

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.