Spring Data Rest新增Comment时报外键空指针异常求助

问题核心 #

调用POST接口新增Comment记录时，触发department_id非空约束错误，服务器未正确接收传入的外键值。

错误信息 #

{
   "cause": {
        "cause": {
            "cause": null,
            "message": "ERROR: null value in column \"department_id\" of relation \"comments\" violates not-null constraint\n  Detail: Failing row contains (32, null, null, null, null, null)."
        },
        "message": "could not execute statement"
    }
}

相关实体代码 #

Comment实体（省略getter/setter） #

@Table(name="comments")
public class Comment implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @SequenceGenerator(name="SEQUENCE_FOR_COMMENTS", sequenceName="SEQUENCE_FOR_COMMENTS",allocationSize = 1 )
    @GeneratedValue(strategy=GenerationType.AUTO, generator="SEQUENCE_FOR_COMMENTS")
    @Column(name="comment_id")
    private Integer commentId;

    private String comment;

    @ManyToOne
    @JoinColumn(name="department_id")
    private Department department;
}

Department实体（省略getter/setter） #

public class Department implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO, generator="SEQUENCE_FOR_Department" )
    @Column(name="department_id")
    private Long departmentId;
}

问题原因 #

请求体字段名不匹配：Postman请求中使用的字段是departmentv1，但Comment实体中对应的关联属性名为department，Jackson无法将请求体的字段映射到实体属性，导致department为null，最终触发department_id非空约束。

解决方案 #

方案1：修正请求体字段名 #

将Postman请求体中的departmentv1改为department，确保与实体属性名一致：

{
    "department": {
        "departmentId": 163
    },
    "comment": "Apr292023"
}

方案2：遵循Spring Data Rest关联资源规范（推荐） #

Spring Data Rest更推荐通过关联资源的URI传递关联关系，符合REST规范：

{
    "comment": "Apr292023",
    "department": "http://localhost:8080/departments/163"
}

（替换为你实际的Department资源URI）

额外验证 #

• 确保Comment和Department实体都有正确的getter/setter方法，Jackson依赖这些方法完成属性赋值。
• 确认数据库表中department_id的非空约束是否符合业务逻辑，若无需非空可调整约束，但不推荐随意修改。

内容的提问来源于stack exchange，提问作者Saimuga