Spring Boot JPA One to One

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Lets learn how to use Spring Boot JPA to implement One to One relationship.

You can model One-to-One relationships between entities using the @OneToOne annotation. In a one-to-one relationship, each record in one table is associated with one and only one record in another table.

Bidirectional One-to-One Relationship

We can have two entities Person and Address. A person can have only one address and an address belongs to only one person.

Person entity:

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@Entity
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    @OneToOne(mappedBy = "person")
    private Address address;

    // getters and setters
}

The @OneToOne annotation is used to create a one-to-one relationship between the Person and Address entities. The mappedBy attribute is used to specify the property in the Address entity that owns the relationship.

Address entity:

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@Entity
public class Address {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String street;
    private String city;

    @OneToOne
    @JoinColumn(name = "person_id")
    private Person person;

    // getters and setters
}

An address belongs to only one person. The @JoinColumn annotation is used to specify the foreign key column in the Address entity that refers to the primary key column in the Person entity.

Test the relationship by creating a Person and an Address and setting the address to the person.

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Person person = new Person();
person.setName("Alice");

Address address = new Address();
address.setStreet("123 Main St");
address.setCity("Springfield");

person.setAddress(address);
address.setPerson(person);

personRepository.save(person);

Unidirectional One-to-One Relationship

It is also possible to create a unidirectional one-to-one relationship.

Person entity:

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@Entity
public class Person {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String name;

    // getters and setters
}

Address entity:

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@Entity
public class Address {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    private String street;
    private String city;

    @OneToOne
    @JoinColumn(name = "person_id")
    private Person person;

    // getters and setters
}

Test:

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Person person = new Person();
person.setName("Alice");

Address address = new Address();
address.setStreet("123 Main St");
address.setCity("Springfield");

address.setPerson(person);

addressRepository.save(address);