JoinColumn.md

@JoinColumn Annotation

The @JoinColumn annotation is used to specify the mapping of a persistent property or field as a foreign key column in a database table.

Attributes

1. name (Required): Specifies the name of the column in the database table.

2. foreignKey (Optional): Specifies the foreign key constraint for the column.

Usage

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface JoinColumn {

    /**
     * Specifies the name of the column.
     *
     * @return the name of the column
     */
    String name();

    /**
     * Specifies the foreign key constraint for the column.
     *
     * @return the foreign key constraint for the column
     */
    ForeignKey foreignKey() default @ForeignKey(name = "");
}

Examples

Basic Usage

@Entity
@Table(name = "employees")
public class Employee {
    @Id
    private Long id;
    
    @ManyToOne
    @JoinColumn(name = "department_id")
    private Department department;

    // Other fields and methods
}

In this example, the Employee entity class has a department field mapped as a foreign key column named "department_id" in the database table.

Join Column with Foreign Key Constraint

@Entity
public class Order {
    @Id
    private Long id;
    
    @OneToOne
    @JoinColumn(name = "customer_id", foreignKey = @ForeignKey(name = "fk_order_customer"))
    private Customer customer;

    // Other fields and methods
}

In this example, the Order entity class has a customer field mapped as a foreign key column named "customer_id" in the database table. Additionally, a foreign key constraint named "fk_order_customer" is specified for the column.

See Also

• @OneToOne
• @ManyToOne
• Schema Generation