在Spring Data Rest中保持OneToMany关系

Question

I have a class called jobprofile, which contains the following OneToMany Relation:

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER, mappedBy = "profile")
private List<JobLanguageProficiency> jobLanguageProficiency;

The referenced class "JobLanguageProficiency" looks like this:

package ch.alv.jobmatch.entity.aux;

import ch.alv.jobmatch.entity.job.Jobprofile;

import javax.persistence.*;


@Entity
@Table(name = "job_language_proficiency")
public class JobLanguageProficiency {

    @Id
    private int id;

    @ManyToOne
    @JoinColumn(name = "jobprofile_jobprofile_id")
    private Jobprofile profile;

    @OneToOne
    private Languages languages;

    @OneToOne
    private LangProficiency langProficiency;

    public Languages getLanguages() {
        return languages;
    }

    public void setLanguages(Languages languages) {
        this.languages = languages;
    }

    public LangProficiency getLangProficiency() {
        return langProficiency;
    }

    public void setLangProficiency(LangProficiency langProficiency) {
        this.langProficiency = langProficiency;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public Jobprofile getProfile() {
        return profile;
    }

    public void setProfile(Jobprofile profile) {
        this.profile = profile;
    }
}

Basically, it just contains two references to a language, and a proficiency for it.

When I try to create/persist a jobprofile, it fails as soon as it tries to insert the language data in the database.

This is the error:

Failed to write HTTP message: org.springframework.http.converter.HttpMessageNotWritableException:

Could not write content: (was java.lang.NullPointerException) (through reference chain: org.springframework.data.rest.webmvc.json.["content"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: (was java.lang.NullPointerException) (through reference chain: org.springframework.data.rest.webmvc.json.["content"])

I suspect the source of the error lies in the JSON, since the OneToMany Relation works perfectly when I insert the data manually.

The relevant part of the JSON looks like this:

job_language_proficiency: Array[1]
    0: Object
        languages: "http://localhost:9000/api/languages/de"
        proficiency_code: "http://localhost:9000/api/langproficiency/C1"

Any ideas why this doesn't work?

EDIT: Updated the JSON so it contains objects instead of links.

LangProficiency entity:

package ch.alv.jobmatch.entity.aux;

import javax.persistence.*;


@Entity
@Table(name = "LangProficiency")
public class LangProficiency {

@Id
@Column(name = "proficiency_code")
private String proficiency_code;

private String description_de;

private String description_fr;

private String description_it;

private String description_en;

public String getProficiency_code() {
    return proficiency_code;
}

public void setProficiency_code(String proficiency_code) {
    this.proficiency_code = proficiency_code;
}

public String getDescription_de() {
    return description_de;
}

public void setDescription_de(String description_de) {
    this.description_de = description_de;
}

public String getDescription_fr() {
    return description_fr;
}

public void setDescription_fr(String description_fr) {
    this.description_fr = description_fr;
}

public String getDescription_it() {
    return description_it;
}

public void setDescription_it(String description_it) {
    this.description_it = description_it;
}

public String getDescription_en() { return description_en; }

public void setDescription_en(String description_en) { this.description_en = description_en; }
}

Languages entity:

package ch.alv.jobmatch.entity.aux;

import javax.persistence.*;
import java.io.Serializable;

@Entity
@Table(name = "Languages")
public class Languages implements Serializable {

@Id
@Column(name = "languages")
private String languages;

private String description_de;

private String description_fr;

private String description_it;

private String description_en;

public String getLanguages() {
    return languages;
}

public void setLanguages(String languages) {
    this.languages = languages;
}

public String getDescription_de() {
    return description_de;
}

public void setDescription_de(String description_de) {
    this.description_de = description_de;
}

public String getDescription_fr() {
    return description_fr;
}

public void setDescription_fr(String description_fr) {
    this.description_fr = description_fr;
}

public String getDescription_it() {
    return description_it;
}

public void setDescription_it(String description_it) {
    this.description_it = description_it;
}

public String getDescription_en() { return description_en; }

public void setDescription_en(String description_en) { this.description_en = description_en; }
}

Answer 1

Your JSON structure should match your Java Mapping, otherwise your object won't be persisted by your ORM, that's why you are getting such Mapping error.

In your case in your Entity you have a relationship with two entities that should be object s in your JSON:

@OneToOne
private Languages languages;

@OneToOne
private LangProficiency langProficiency;

But in your JSON, you have set those two objects as simple strings:

languages: "http://localhost:9000/api/languages/de"
proficiency_code: "http://localhost:9000/api/langproficiency/C1"

They should be matching Languages and langProficiency objects, and proficiency_code should be named langProficiency respectively like your Java attribute.