JPA Annotations(Overview)

💎 Java Annotations

• ⚾Step1: Map class to database table

Java Class -- Database Table

@Entity
@Table(name="student")
public class Student{
}

• ⚾ Step2: Map fields to database columns

@Entity
@Table(name="student")
public class Student{
	@Id
    @Column(name="id")
    private int id;
    
    @Column(name="first_name")
    private String firstName;
	...
}

💎@Column - Optional

• Not recommend this approach
• This is a breaking change and you will need to update database column
• @Table is an optional. (Table field name is mapped by class)

⚾ ID Generation Strategies

Name	Description
GenerationType.AUTO	Pick an appropriate strategy for the particular database
GenerationType.IDENTIFY	Assign primary keys using database identify column
GenerationType.SEQUENCE	Assign primary keys using a database sequence

• 코드 작성해보기

package com.hongJpa.hongdemo.entity;


import jakarta.persistence.*;

// Map class to database table
@Entity
@Table(name="student")
public class Student {
    // define fields
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="id")
    private Integer id;

    @Column(name="first_name")
    private String firstName;

    @Column(name="last_name")
    private String lastName;

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

    public Student() {

    }

    // define constructors
    public Student(String firstName, String lastName, String email) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.email = email;
    }

    // define getters/setters

    public Integer getId() {
        return id;
    }

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

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }


    // define toString() method

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                ", email='" + email + '\'' +
                '}';
    }
}