在Spring Data JPA中联接两个实体

Question

I have two tables in a Mysql database: Department and Contact. I connected with my application in the apllication.properties file.

This is my Database:

pom.xml is as Follows:

<?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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.3.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo1</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo1</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <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-thymeleaf</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>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>
    </dependencies>

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

</project>

This is my contact class:

@Entity
@Table(name="contact")
public class Contact {

    @Id
    @Column(name="contact_id")
    private int Contact_id;

    @Column(name="emp_name")
    private String Emp_name;

    @Column(name="mobile")
    private String Mobile;


    @Column(name="landline_office")
    private String Landline_office;

    @Column(name="landline_res")
    private String Landline_res;

    @Column(name="fax")
    private String Fax;

    @Column(name="email")
    private String Email;

    @ManyToOne(cascade= {CascadeType.PERSIST,CascadeType.MERGE,
            CascadeType.DETACH,CascadeType.REFRESH})
    @JoinColumn(name="department_dept_id")
    private Department department;

... constructors and getters and setters

This is my department class:

@Entity
@Table(name="department")
public class Department {

    @Id
    @Column(name="dept_id")
    private int Dept_id;

    @Column(name="dept_name")
    private String Dept_name;

    @Column(name="order")
    private String Order;

    @Column(name="home")
    private int Home;

    @OneToMany(mappedBy="department",
            cascade= {CascadeType.PERSIST,CascadeType.MERGE,
                    CascadeType.DETACH,CascadeType.REFRESH})
    private List<Contact> contacts;

    public Department() {

    }

...getters and setters and constructors

I can display the first entity: Department in table using thymeleaf:

What I want to do is: Dynamically display all employees belonging to ICT when i click View button in row 1 and so for PWD.

I have uploaded the project in github: https://github.com/sammizodev/Jpa_two_tables

Answer 1

Here is a code review of the code you post:

Naming conventions : You should take a look at java naming conventions , class attributes should follow camel case syntax, use of underscore is disregard.

Above does not need to impact your database schema, as you can use @Column to do the mapping between your table field and class attribute, for instance:

@Id
@Column(name="dept_id")
private int id;

@Column(name="dept_name")
private String name;

@Column(name="dept_order")
private String Order;

Notice, order is a keyword in many database, so you may need to change it.

Restful Conventions : I would suggest you to take a look at restful API design , then you can understand how to structure your application to access certain resources.

According to conventions, you have one resource(department) and you would need these URI:

• URI: GET /department - /department/list.html - Render table of department
• URI: GET /department/{id} - /department/show.html - Render a department with details(contact table).

For instance, you have GET /departments_list to render your department list, you would need instead to change it to GET /departments and your template should be named list.html.

@GetMapping("/departments")
public String listDepartments(Model model) {
    List<Department> departments = departmentService.findAll();
    model.addAttribute("departments",departments);
    return "/departments/list"; // Your current thymeleaf template
}

Then you would need a GET /departments/{id} in order to render the department details including the list of contacts.

So on your department list template you should build the link like:

<a th:href="@{/home/contact/{departmentId}(departmentId=${tempDepartment.dept_id})}"
                class="btn btn-info btn-sm">View</a>

Notice, you need to provide the url like /home/contact/{departmentId} so tymeleaf can replace the id property, otherwise you will received as a parameter.

On your controller you need to update the mapping to the contacts to include the id as a path variable:

@GetMapping("/departments/{id}")
public String listContacts(@PathVariable("id") int theId, Model theModel) {
        Department department = departmentService.findById(theId);
        theModel.addAttribute("department",department);
        return "/departments/show";
}

If your Department class loads contacts eager, you could access the list in your front-end in a show.html template.

<tr th:each="contact : ${department.contacts}">     
    <td th:text="${contact.contact_id}" />  
    <td th:text="${contact.emp_name}" />    
    <td th:text="${contact.mobile}" />  
    <td th:text="${contact.landline_office}" />         
</tr>

Also, remember to wire the ContactService at your DemoController .

public DemoController(DepartmentService departmentService, ContactService contactService) {
        this.departmentService = departmentService;
        this.contactService = contactService;
    }