SpringBoot - Server Won't Start; Unknown 'mappedBy' Error

Question

I'm relatively new to SpringBoot, and I've been following this tutorial on SpringBoot + React on Udemy called "Full Stack Project: Spring Boot 2.0, ReactJS, Redux."

I am no longer able to start my server. I am getting this error:

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2022-02-22 07:58:57.885 ERROR 33860 --- [  restartedMain] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is org.hibernate.AnnotationException: Unknown mappedBy in: com.jonjackson.ppmtool.domain.Backlog.projectTasks, referenced property unknown: java.util.List.backlog
...
Caused by: org.hibernate.AnnotationException: Unknown mappedBy in: com.jonjackson.ppmtool.domain.Backlog.projectTasks, referenced property unknown: java.util.List.backlog

I think this error may have something to do with the value that I am passing in the mappedBy in a @OneToOne or @ManyToOne annotation, but I am not sure what I have done differently than the tutorial. Does anyone see the issue here?

The files that are referenced in the error are:

ProjectTask.java

package com.jonjackson.ppmtool.domain;

import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonIgnore;

import javax.persistence.*;
import javax.validation.constraints.NotBlank;
import java.util.Date;

@Entity
public class ProjectTask {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(updatable = false, unique = true)
    private String projectSequence;
    //header for projectTask
    @NotBlank(message = "Please include a project summary")
    private String summary;
    private String acceptanceCriteria;
    private String status;
    private Integer priority;
    @JsonFormat(pattern = "yyyy-mm-dd")
    private Date dueDate;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name="backlog_id", updatable = false, nullable = false)
    @JsonIgnore
    private Backlog backlog;

    @Column(updatable = false)
    private String projectIdentifier;
    @JsonFormat(pattern = "yyyy-mm-dd")
    private Date create_At;
    @JsonFormat(pattern = "yyyy-mm-dd")
    private Date update_At;

    public ProjectTask(){
    }

    public Long getId() {
        return id;
    }

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

    public String getProjectSequence() {
        return projectSequence;
    }

    public void setProjectSequence(String projectSequence) {
        this.projectSequence = projectSequence;
    }

    public String getSummary() {
        return summary;
    }

    public void setSummary(String summary) {
        this.summary = summary;
    }

    public String getAcceptanceCriteria() {
        return acceptanceCriteria;
    }

    public void setAcceptanceCriteria(String acceptanceCriteria) {
        this.acceptanceCriteria = acceptanceCriteria;
    }

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public Integer getPriority() {
        return priority;
    }

    public void setPriority(Integer priority) {
        this.priority = priority;
    }

    public Date getDueDate() {
        return dueDate;
    }

    public void setDueDate(Date dueDate) {
        this.dueDate = dueDate;
    }

    public String getProjectIdentifier() {
        return projectIdentifier;
    }

    public void setProjectIdentifier(String projectIdentifier) {
        this.projectIdentifier = projectIdentifier;
    }

    public Date getCreate_At() {
        return create_At;
    }

    public void setCreate_At(Date create_At) {
        this.create_At = create_At;
    }

    public Date getUpdate_At() {
        return update_At;
    }

    public void setUpdate_At(Date update_At) {
        this.update_At = update_At;
    }

    public Backlog getBacklog() {
        return backlog;
    }

    public void setBacklog(Backlog backlog) {
        this.backlog = backlog;
    }

    @PrePersist
    protected void onCreate(){
        this.create_At = new Date();
    }

    @PreUpdate
    protected void onUpdate(){
        this.update_At = new Date();
    }

    @Override
    public String toString() {
        return "ProjectTask{" +
                "id=" + id +
                ", projectSequence='" + projectSequence + '\'' +
                ", summary='" + summary + '\'' +
                ", acceptanceCriteria='" + acceptanceCriteria + '\'' +
                ", status='" + status + '\'' +
                ", priority=" + priority +
                ", dueDate=" + dueDate +
                ", projectIdentifier='" + projectIdentifier + '\'' +
                ", create_At=" + create_At +
                ", update_At=" + update_At +
                '}';
    }
}

Backlog.java

package com.jonjackson.ppmtool.domain;

import com.fasterxml.jackson.annotation.JsonIgnore;

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;

@Entity
public class Backlog {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private Integer PTSequence = 0;
    private String projectIdentifier;


    @OneToOne(fetch = FetchType.EAGER)
    @JoinColumn(name="project_id", nullable = false)
    @JsonIgnore
    private Project project;

    //OneToMany with projecttasks (a backlog can have one or more projecttasks, but a projecttask can belong to one project)
    @OneToOne(cascade = CascadeType.REFRESH, fetch = FetchType.EAGER, mappedBy = "backlog", orphanRemoval = true)
    private List<ProjectTask> projectTasks = new ArrayList<>();

    public Backlog(){
    }

    public Long getId() {
        return id;
    }

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

    public Integer getPTSequence() {
        return PTSequence;
    }

    public void setPTSequence(Integer PTSequence) {
        this.PTSequence = PTSequence;
    }

    public String getProjectIdentifier() {
        return projectIdentifier;
    }

    public void setProjectIdentifier(String projectIdentifier) {
        this.projectIdentifier = projectIdentifier;
    }

    public Project getProject() {
        return project;
    }

    public void setProject(Project project) {
        this.project = project;
    }

    public List<ProjectTask> getProjectTasks() {
        return projectTasks;
    }

    public void setProjectTasks(List<ProjectTask> projectTasks) {
        this.projectTasks = projectTasks;
    }
}

and here is the main Project class:

Project.java

package com.jonjackson.ppmtool.domain;

import com.fasterxml.jackson.annotation.JsonFormat;

import javax.persistence.*;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.Size;
import java.util.Date;

@Entity
public class Project {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @NotBlank(message = "Project name is required")
    private String projectName;
    @NotBlank(message = "Project Identifier is required")
    @Size(min = 4, max = 5, message = "Please use 4 to 5 characters")
    @Column(updatable = false, unique = true)
    private String projectIdentifier; //adding custom identifier for Project {}
    @NotBlank(message = "Project Description is required")
    private String description;
    @JsonFormat(pattern = "yyyy-mm-dd")
    private Date start_date;
    @JsonFormat(pattern = "yyyy-mm-dd")
    private Date end_date;
    @JsonFormat(pattern = "yyyy-mm-dd")
    @Column(updatable = false)
    private Date created_at;
    @JsonFormat(pattern = "yyyy-mm-dd")
    private Date updated_at;

    @OneToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL, mappedBy = "project")
    private Backlog backlog;

    public Project() {
    }

    public Long getId() {
        return id;
    }

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

    public String getProjectName() {
        return projectName;
    }

    public void setProjectName(String projectName) {
        this.projectName = projectName;
    }

    public String getProjectIdentifier() {
        return projectIdentifier;
    }

    public void setProjectIdentifier(String projectIdentifier) {
        this.projectIdentifier = projectIdentifier;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public Date getStart_date() {
        return start_date;
    }

    public void setStart_date(Date start_date) {
        this.start_date = start_date;
    }

    public Date getEnd_date() {
        return end_date;
    }

    public void setEnd_date(Date end_date) {
        this.end_date = end_date;
    }

    public Date getCreated_at() {
        return created_at;
    }

    public void setCreated_at(Date created_at) {
        this.created_at = created_at;
    }

    public Date getUpdated_at() {
        return updated_at;
    }

    public void setUpdated_at(Date updated_at) {
        this.updated_at = updated_at;
    }

    public Backlog getBacklog() {
        return backlog;
    }

    public void setBacklog(Backlog backlog) {
        this.backlog = backlog;
    }

    @PrePersist
    protected void onCreate() {
        this.created_at = new Date();
    }

    @PreUpdate
    protected void onUpdate() {
        this.updated_at = new Date();
    }
}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>io.agileintelligence</groupId>
    <artifactId>ppmtool</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>ppmtool</name>
    <description>Personal Project Management Tool</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-api -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.7.1</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.junit.jupiter/junit-jupiter-engine -->
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-engine</artifactId>
            <version>5.7.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter</artifactId>
            <version>RELEASE</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

Answer 1

you should only put mappedBy once on one side of the relationship. The one that you want to do the "mapping"

in your case maybe remove mappedBy from backlog entity