[Annotation] JPA Annotation and JPQL API

Annotation Id

• Specifies the primary key of an entity.

Annotation Column

• Is used to specify the mapped column for a persistent property or field.
• If no Column annotation is specified, the default values apply.
• 如果名稱相同，則不需要使用此指定。

Annotation GeneratedValue

• Provides for the specification of generation strategies for the values of primary keys.
• String generator
• (Optional) The name of the primary key generator to use as specified in the SequenceGenerator or TableGenerator annotation.
• GenerationType strategy (Refer the next)
• (Optional) The primary key generation strategy that the persistence provider must use to generate the annotated entity primary key.
• Default value:
• javax.persistence.GenerationType.AUTO

Enum GenerationType

• GenerationType AUTO
• Default for Annotation GeneratedValue
• GenerationType IDENTITY
• GenerationType SEQUENCE
• Indicates that the persistence provider must assign primary keys for the entity using a database sequence.
• GenerationType TABLE

Annotation ManyToOne

• Defines a single-valued association to another entity class that has many-to-one multiplicity.
• It is not normally necessary to specify the target entity explicitly since it can usually be inferred from the type of the object being referenced.
• The ManyToOne annotation may be used within an embeddable class to specify a relationship from the embeddable class to an entity class.
• CascadeType[] cascade
• (Optional) The operations that must be cascaded to the target of the association.
• By default no operations are cascaded.
• FetchType fetch
• (Optional) (refer the following items)
• Default value:
• javax.persistence.FetchType.EAGER

Enum CascadeType

• Defines the set of cascadable operations that are propagated to the associated entity.
• The value cascade=ALL is equivalent to cascade={PERSIST, MERGE, REMOVE, REFRESH, DETACH}.

Enum FetchType

• Defines strategies for fetching data from the database.
• The EAGER strategy
• A requirement on the persistence provider runtime that data must be eagerly fetched. 
• The LAZY strategy
• A hint to the persistence provider runtime that data should be fetched lazily when it is first accessed.
• The implementation is permitted to eagerly fetch data for which the LAZY strategy hint has been specified.

Annotation JoinColumn

• Specifies a column for joining an entity association or element collection.
• String referencedColumnName

Interface CriteriaBuilder

• Used to construct criteria queries, compound selections, expressions, predicates, orderings.
• Note that Predicate is used instead of Expression in this API in order to work around the fact that Java generics are not compatible with varags. (?)

Interface CriteriaQuery<T>

• The CriteriaQuery interface defines functionality that is specific to top-level queries.

Interface Root<X>

• A root type in the from clause. Query roots always reference entities.

* Reference
- JPA Reference (JavaDoc)