jpa-entity-graph.md

❓ What is @EntityGraph?

When you load an entity (like User, Order, etc.), related entities (like roles, addresses, etc.) are not fetched immediately if they are marked as LAZY. This can lead to:

• N+1 select problem (lots of tiny SQL queries),
• Or LazyInitializationException when accessing a lazy field outside the transaction.

@EntityGraph lets you tell JPA exactly which relationships to fetch eagerly in a specific query, without changing your entity mappings.

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🧠 Think of it like:

“I want to fetch User along with their roles, but I don’t want to mark roles as EAGER in the entity itself. Just for this query, fetch it eagerly.”

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🧾 Example

Suppose you have this:

@Entity
public class User {
  @Id
  private Long id;

  private String name;

  @ManyToOne(fetch = FetchType.LAZY)
  private Role role;
}

Now let’s say you want to fetch the User with its Role eagerly in one query.

✅ Without @EntityGraph:

@Query("select u from User u join fetch u.role where u.name = ?1")
User findByName(String name);

Problem: You must write custom JPQL, and it always fetches role.

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✅ With @EntityGraph:

@EntityGraph(attributePaths = "role")
User findByName(String name);

Much cleaner! This tells Spring Data JPA:

When running this method, join fetch the role too.

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🔁 Multiple attributes:

@EntityGraph(attributePaths = {"role", "address", "company"})
User findByName(String name);

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🔄 Use with @Query (optional):

@Query("select u from User u where u.name = ?1")
@EntityGraph(attributePaths = "role")
User findByName(String name);

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📝 Notes:

• You don’t need to change LAZY to EAGER in your entities.
• It helps avoid performance problems (like N+1 queries).
• You can even define named entity graphs in the entity class and refer to them.

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📌 Summary

Annotation	Purpose
@EntityGraph	Fetch specific relationships eagerly in a query
attributePaths	List of fields (relationships) to fetch eagerly
Works with	Repository methods, @Query, or both

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