Hibernate generates extra left join with many to one association

Question

I have a simple Hibernate @ManyToOne mapping between two entities, using an association table thanks to annotation @JoinTable. Here is my mapping:

@Entity
public class Customer {

    private Long id;
    private Address address;

    @Id
    @GeneratedValue
    public Long getId() {
        return id;
    }


    @ManyToOne
    @JoinTable(
            name = "customer_address_association",
            joinColumns = @JoinColumn(name = "customer_id"),
            inverseJoinColumns = @JoinColumn(name = "address_id")
    )
    public Address getAddress() {
        return address;
    }

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

    public void setAddress(Address address) {
        this.address = address;
    }
}

and

@Entity
public class Address {

    private Long id;
    private String street;

    @Id
    @GeneratedValue
    public Long getId() {
        return id;
    }

    public String getStreet() {
        return street;
    }

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

    public void setStreet(String street) {
        this.street = street;
    }
}

When I query on Customer entity, I always get an extra left join to the join table. For example, a HQL query such as SELECT c.id from Customer c generates the following SQL query: select customer0_.id as col_0_0_ from customer customer0_ left outer join customer_address_association customer0_1_ on customer0_.id=customer0_1_.customer_id.

Full source code to reproduce is available here: https://github.com/ndionisi/hibernate-extra-left-join

I reproduce it with Hibernate 5.1, 5.2 and 5.3. Is there any way to prevent Hibernate from generating the left join to customer_address_association table? It impacts the performance on large tables.

Answer 1

I recommend using FetchType.LAZY on the @ManyToOne annotation.