How can multiple tables be queried together in Spring Boot?

2 years ago
Noah Thompson
2 minutes

In Spring Boot, you can perform multi-table queries using JPA (Java Persistence API) and Hibernate.

Here is a common method for performing a multiple table join:

  1. Create entity classes: First, create entity classes corresponding to each table, and use annotations to map them to the tables in the database.
@Entity
@Table(name = "table1")
public class Table1 {
    @Id
    private Long id;
    private String name;
    // getters and setters
}

@Entity
@Table(name = "table2")
public class Table2 {
    @Id
    private Long id;
    private String description;
    // getters and setters
}
  1. Mapping between two entities in a one-to-one relationship.
  2. – One-to-Many
  3. Used to define a many-to-one relationship in a database mapping.
  4. A relationship where each instance of one entity can be associated with multiple instances of another entity.
@Entity
@Table(name = "table1")
public class Table1 {
    @Id
    private Long id;
    private String name;

    @OneToOne(mappedBy = "table1")
    private Table2 table2;
    
    // getters and setters
}

@Entity
@Table(name = "table2")
public class Table2 {
    @Id
    private Long id;
    
    @OneToOne
    @JoinColumn(name = "table1_id")
    private Table1 table1;

    // getters and setters
}
  1. A repository for handling basic CRUD operations.
  2. A repository that provides methods for easy interaction with a database in a Spring application is referred to as JpaRepository.
public interface Table1Repository extends JpaRepository<Table1, Long> {
}

public interface Table2Repository extends JpaRepository<Table2, Long> {
}
  1. Performing multi-table queries: In the business logic layer or service layer, you can use JPA’s query methods as needed to perform multi-table queries.
@Service
public class MyService {
    @Autowired
    private Table1Repository table1Repository;
    
    @Autowired
    private Table2Repository table2Repository;
    
    public List<Table1> getTable1WithTable2() {
        return table1Repository.findAll();  // 返回所有Table1，并自动联查关联的Table2
    }
}

The above method can conveniently perform multi-table queries. Additionally, more complex multi-table queries can also be achieved using native SQL queries, JPQL queries, and other methods.

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