Top 10 questions for @Query annotation in Spring Data

What is the @Query annotation used for in Spring?
Defines custom JPQL or native SQL queries in Spring Data JPA repositories for precise data retrieval or manipulation.

How do you write a JPQL query using @Query?
Use @Query("SELECT e FROM Entity e WHERE e.field = :param") in a repository method, binding parameters with @Param.

Can @Query be used for native SQL queries?
Yes, set nativeQuery = true in @Query to execute native SQL, e.g., @Query(value = "SELECT * FROM table", nativeQuery = true).

How do you pass parameters to @Query?
Use :? or @Param("name"), e.g., @Query("SELECT e FROM Entity e WHERE e.field = :name") with method parameter @Param("name") String value.

What’s the difference between JPQL and native SQL in @Query?
JPQL queries operate on entities and are database-agnostic; native SQL queries are database-specific and use raw SQL.

How do you handle pagination with @Query?
Add Pageable as a method parameter, e.g., @Query("SELECT e FROM Entity e") Page<Entity> findAll(Pageable pageable).

Can @Query be used for update or delete operations?
Yes, with @Modifying, e.g., @Modifying @Query("UPDATE Entity e SET e.field = :value") for updates.

How do you use @Query with LIKE in JPQL?
Use LIKE in the query, e.g., @Query("SELECT e FROM Entity e WHERE e.field LIKE %:pattern%") for pattern matching.

What happens if @Query syntax is incorrect?
Spring throws a runtime exception (e.g., InvalidJpaQueryMethodException) during application startup or query execution.

Can @Query return custom DTOs instead of entities?
Yes, use a constructor expression in JPQL, e.g., @Query("SELECT new com.example.MyDto(e.field1, e.field2) FROM Entity e").