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How does javax.persistence.fetchgraph differ from javax.persistence.loadgraph when providing an EntityGraph hint to a JPA 2.1 query? The documentation isn't really clear.
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The @NamedEntityGraph annotation allows specifying the attributes to include when we want to load the entity and the related associations. In this example, we've used the @NamedAttributeNode to define the related entities to be loaded when the root entity is loaded.
No fields are included in the @NamedEntityGraph annotation as attribute nodes, and the fields are not annotated with metadata to set the fetch type, so the only field that will be eagerly fetched in either a load graph or fetch graph is messageId .
1. Overview. Simply put, Entity Graphs are another way to describe a query in JPA 2.1. We can use them to formulate better-performing queries. In this tutorial, we're going to learn how to implement Entity Graphs with Spring Data JPA through a simple example.
Let's start with an overview of the entity graph. Entity Graph is introduced in JPA 2.1 for dealing with performance loading. The definition of an entity graph is independent of the query and defines which attributes to fetch from the database.
When using fetchgraph all relationships are considered to be lazy regardless of annotation, and only the elements of the provided graph are loaded. This particularly useful when running reports on certain objects and you don't want a lot of the stuff that's normally flagged to load via eager annotations.
If you want to eagerly load entities that are normally loaded via lazy annotation, you may use loadgraph to add entities to the query results that would normally be loaded later, thereby avoiding specific N+1 cases. Relationships that were already flagged as eager will continue to be loaded as usual.
See https://docs.oracle.com/javaee/7/tutorial/persistence-entitygraphs001.htm
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