使用 CrudRepository 保存带有外键的实体对象

Question

I have two entity classes with @ManyToOne relationship as below.

@Entity
public class Student {

  @Id
  private Integer studentId;

  @Column(nullable = false)
  private String studentName;

  @ManyToOne(targetEntity = School.class, fetch = FetchType.LAZY, optional = false)
  @JoinColumn(referencedColumnName = "schoolId", insertable = false, updatable = false)
  private School school;

  //Getters and Setters methods

.

@Entity
public class School {
  @Id
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer schoolId;

  @Column(nullable = false)
  private String schoolName;

  //Getters and Setters methods

When I try to save the student object using CrudRepository default method studentRepository.save(student) with JSON payload, it gives me an error java.sql.SQLException: Field 'school_id' doesn't have a default value . When I run in the debug mode I can see that the School object is being set correctly.

My JSON payload is as follows:

[
    {
      "studentId": "2015020",
      "studentName": "ABC",
      "school": {
        "schoolId": 1
      }
    }
]

I am new to Spring Data JPA, so this might be a very basic mistake.

Answer 1

You could try to change the column name collegeId to schoolId in table school , and then modify this line:

@ManyToOne(targetEntity = School.class, fetch = FetchType.LAZY, optional = false)
@JoinColumn(referencedColumnName = "schoolId", insertable = false, updatable = false)
private School school;

Answer 2

In the entity Student the property school is an object. To insert new student you must use a reference to school object. So your payload must be like this:

{
    "studentId": 2015020,
    "studentName": "ABC",
    "school": "http://localhost:8080/api/schools/1"
}

Also you can simplify the definition of the property school :

@ManyToOne(optional = false)
private School school;

Answer 3

Just check if the name of database column match with entity mapping: If identity column of school table in DB is "school_id", mention it in your mapping:

  @Id
  @Column(name = "school_id")
  @GeneratedValue(strategy = GenerationType.AUTO)
  private Integer schoolId;