(1) Add Spring Data JPA dependent initiator. Add the Spring Data JPA dependent initiator to the project’s POM.xml file as shown in the following example code

<dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
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(2) Write ORM entity classes.

@Entity(name = "t_comment") // Set the ORM entity class and specify the table name for the mapping
public class Comment {
 
 @Id // Indicates the primary key ID of the mapping
 @GeneratedValue(strategy = GenerationType.IDENTITY) // Set the policy for increasing the primary key
 private Integer id;
 private String content;
 private String author;
 
 @Column(name = "a_id") // Specify the table field name for the mapping
 private Integer aId;
 // Omit the property getXX() and setXX() methods
  // omit the toString() method
 }
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(3) Write Repository interface: CommentRepository

public interface CommentRepository extends JpaRepository<Comment.Integer> {}Copy the code

(4) Test

 @Autowired
 private CommentRepository repository;
 
 @Test
 public void selectComment(a) {
 Optional<Comment> optional = repository.findById(1);
 if(optional.isPresent()){
System.out.println(optional.get());
 }
System.out.println();
 
 }
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Print:

<imgsrc=”./images/image-20191227175837216.png” alt=”image-20191227175837216″ style=”zoom:67%;” />

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