How To Use Entity Graphs For @Basic Attributes In Hibernate And Spring Boot

Note: In a nutshell, entity graphs (aka, fetch plans) is a feature introduced in JPA 2.1 that help us to improve the performance of loading entities. Mainly, we specify the entity’s related associations and basic fields that should be loaded in a single SELECT statement. We can define multiple entity graphs for the same entity and chain any number of entities and even use sub-graphs to create complex fetch plans. To override the current FetchType semantics there are properties that can be set:

Fetch Graph (default), javax.persistence.fetchgraph
The attributes present in attributeNodes are treated as FetchType.EAGER. The remaining attributes are treated as FetchType.LAZY regardless of the default/explicit FetchType.

Load Graph, javax.persistence.loadgraph
The attributes present in attributeNodes are treated as FetchType.EAGER. The remaining attributes are treated according to their specified or default FetchType.

Nevertheless, the JPA specs doesn't apply in Hibernate for the basic (@Basic) attributes. In other words, by default, attributes are annotated with @Basic which rely on the default fetch policy. The default fetch policy is FetchType.EAGER. These attributes are also loaded in case of fetch graph even if they are not explicitly specified via @NamedAttributeNode. Annotating the basic attributes that should not be fetched with @Basic(fetch = FetchType.LAZY) it is not enough. Both, fetch graph and load graph will ignore these settings as long as we don't add bytecode enhancement as well.

The main drawback consists of the fact the these basic attributes are fetched LAZY by all other queries (e.g., findById()) not only by the queries using the entity graph, and most probably, you will not want this behavior.

Description: This is a sample application of using entity graphs with @Basic attributes in Spring Boot.

Key points:

• define two entities, Author and Book, involved in a lazy bidirectional @OneToMany association
• in Author entity use the @NamedEntityGraph to define the entity graph (e.g., load the authors names (only the name basic attribute; ignore the rest) and the associatated books)
• add bytecode enhancement
• annotate the basic attributes that should be ignored by the entity graph with @Basic(fetch = FetchType.LAZY)
• in AuthorRepository rely on Spring @EntityGraph annotation to indicate the entity graph defined at the previous step

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