difference between FetchMode and FetchType

Question

what is the difference in specifying lazy = \"true\" and using fetch = \"select\" or \"join\" ? which one is preferred over the other ?

Answer 1

Let's say we have entities like this:

@Entity
@Table
public class Parent {
    @Id
    private Long id;

    @OneToMany(mappedBy="parent", fetch = FetchType.EAGER)
    @Fetch(FetchMode.JOIN)
    private List child;    
    //getter setters
}


@Entity
@Table
public class Child {    
    @Id
    private Long id;

    @ManyToOne(fetch = FetchType.LAZY)
    private Parent parent;

    //getter setter
}

In above example, when getting Parent entity, hibernate will automaticly load all child entities eagerly using join. On the other hand, when you fetch Child, Parent entity won't be selected unless you call it explicity in your code child.getParent().

FetchType (Lazy/Eager) tells whether we want entity to be loaded eagerly or lazy, when there's call in code.

FetchMode (Select/Join) tells whether we want our entitity to be loaded with additional select or in one query with join or subselect.