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I'm currently using Eclipselink, but I know now days most JPA implementations have been pretty standardized. Is there a native way to map a JPA entity to a view? I am not looking to insert/update, but the question is really how to handle the @Id annotation. Every entity in the JPA world must have an ID field, but many of the views I have created do not conform to this. Is there native support for this in the JPA or do I need to use hacks to get it to work? I've searched a lot and found very little information about doing this.
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In JPA you can map to a VIEW the same as a table, using the @Table annotation. You can then map each column in the view to your object's attributes. Views are normally read-only, so object's mapping to views are normally also read-only.
The One-To-One mapping represents a single-valued association where an instance of one entity is associated with an instance of another entity. In this type of association one instance of source entity can be mapped atmost one instance of target entity.
Association mappings are one of the key features of JPA and Hibernate. They model the relationship between two database tables as attributes in your domain model. That allows you to easily navigate the associations in your domain model and JPQL or Criteria queries.
We can use the JPA @Lob annotation to map large fields to large database object types.
While using the @Id annotation with fields of directly supported types is not the only way to specify an entity's identity (see @IdClass with multiple @Id annotations or @EmbeddedId with @Embedded), the JPA specification requires a primary key for each entity.
That said, you don't need entities to use JPA with database views. As mapping to a view is no different from mapping to a table from an SQL perspective, you could still use native queries (createNativeQuery on EntityManager) to retrieve scalar values instead.
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