Spring Boot Data Persistence with JPA 5

Question 1

Which Spring Data JPA keyword in a method name generates an IS NULL condition?

Accepted Answer

IsNull

Answer

Appending `IsNull` or `Null` to a field name in a repository method name generates a WHERE field IS NULL clause.

Question 2

What does `@Table(uniqueConstraints = @UniqueConstraint(columnNames = {"email"}))` accomplish?

Accepted Answer

Adds a unique database constraint on the email column during schema generation

Answer

uniqueConstraints tells JPA schema generation to create a UNIQUE constraint on the specified column(s) in the database.

Question 3

Which method on `EntityManager` is used to synchronize a detached entity back to the persistence context?

Accepted Answer

merge()

Answer

merge() copies the state of a detached entity into a new managed instance and returns that managed instance.

Question 4

What problem does the N+1 query issue describe in JPA?

Accepted Answer

Fetching a list of N entities triggers N additional queries for their lazy associations

Answer

N+1 occurs when loading a parent list (1 query) then triggering a separate query for each child association (N queries), totaling N+1 queries.

Question 5

Which JPQL keyword is used to eagerly fetch associations in a single query to avoid N+1?

Accepted Answer

JOIN FETCH

Answer

JOIN FETCH in JPQL instructs Hibernate to include the association in the same SQL SELECT, preventing additional lazy-load queries.

Spring Boot Practice Test