How To Define Ad-Hoc Entity Graphs In 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.. More details here.

Description: This is a sample application of defining ad-hoc entity graphs in Spring Boot.

Key points:

• define two entities, Author and Book, involved in a lazy bidirectional @OneToMany relationship
• the entity graph should load in a single SELECT the authors and the associatated books
• in AuthorRepository rely on Spring @EntityGraph(attributePaths = {"books"}) annotation to indicate the ad-hoc entity graph

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