Spring Data JPA - @Table Annotation

Spring Data JPA provides a convenient way to interact with relational databases through entity mappings.

The @Table annotation is used to customize how an entity class is mapped to a database table. By default, JPA uses the class name as the table name, but with @Table, developers can explicitly define table names, schemas, catalogs, and unique constraints.

Purpose

The @Table annotation is part of the Jakarta Persistence (JPA) specification and is placed above the @Entity annotation in a class.

It is mainly used when:

• The table name in the database differs from the entity class name
• A schema or catalog needs to be defined for database organization
• Unique constraints must be enforced on specific columns

Syntax:

import jakarta.persistence.*;
@Entity
@Table(name = "student")  // Defines custom table name
public class Student { 
    // Fields and methods  
}

By default, JPA would create a table named Student (matching the class name). Using @Table(name = "student"), the table name is explicitly set to student.

Attributes of @Table Annotation

• name: Specifies the name of the database table (default: entity class name)
• catalog: Defines the database catalog name
• schema: Defines the schema name for the table
• uniqueConstraints: Enforces unique constraints on one or more columns

Example: Using @Table with Unique Constraint

import jakarta.persistence.*;

@Entity
@Table(
    name = "EMPLOYEE",
    uniqueConstraints = { @UniqueConstraint(columnNames = "email") }
)
public class Employee {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;

    @Column(nullable = false, unique = true)
    private String email;
}

• The table name is explicitly set to EMPLOYEE.
• A unique constraint is added on the email column, ensuring no two records share the same email address.
• @Column(unique = true) ensures column-level uniqueness, while @UniqueConstraint applies at the table level.

Implementation Steps

Step 1: Create a Spring Boot Project

Use Spring Initializr and include dependencies:

• Spring Web
• Spring Data JPA
• MySQL Driver

Click on Generate, download, and extract the project.

Step 2: Configure Database in application.properties

spring.datasource.url=jdbc:mysql://localhost:3306/mapping
spring.datasource.username=root
spring.datasource.password=your_password
spring.jpa.hibernate.ddl-auto=update

Note: Use environment variables to protect sensitive credentials:

spring:
datasource:
username: ${DB_USER}
password: ${DB_PASS}

Step 3: Create the Entity Class

StudentInformation.java:

package com.example.mapping.model;

import jakarta.persistence.*;

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

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int rollno;
    private String name;

    public StudentInformation() {}
    public StudentInformation(int rollno, String name) {
        this.rollno = rollno;
        this.name = name;
    }

    public int getRollno() { return rollno; }
    public void setRollno(int rollno) { this.rollno = rollno; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}

Step 5: Running the Application

Run the main Spring Boot application class. If everything is configured correctly, Hibernate will generate a table named student in the mapping database.

Database Output: