Java Community | Help. Code. Learn.•7d ago

fetch subclasses and their associations with one query

demo for simplicity and to avoid being sued :GnuTrolling: so the question is whether its possible to fetch all the associations to their respective classes when calling the find all method without eager fetching and avoiding n+1 and without extra queries for getting the associations

public interface ShapeRepository extends JpaRepository<Shape, Long> {
    Page<Shape> findAll();
}

public interface ShapeRepository extends JpaRepository<Shape, Long> {
    Page<Shape> findAll();
}

@DiscriminatorValue("SQUARE")
@Entity
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Square extends Shape {
    @OneToMany(mappedBy = "square", fetch = FetchType.LAZY)
    private Set<Vertices>;
}

@DiscriminatorValue("SQUARE")
@Entity
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Square extends Shape {
    @OneToMany(mappedBy = "square", fetch = FetchType.LAZY)
    private Set<Vertices>;
}

@DiscriminatorValue("TRIANGLE")
@Entity
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Triangle extends Shape {
    @OneToMany(mappedBy = "triangle", fetch = FetchType.LAZY)
    private Set<Angles>;
}

@DiscriminatorValue("TRIANGLE")
@Entity
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Triangle extends Shape {
    @OneToMany(mappedBy = "triangle", fetch = FetchType.LAZY)
    private Set<Angles>;
}

@Entity
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public abstract class Shape {
    @Id
    private long id;

    private String name;
}

@Entity
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public abstract class Shape {
    @Id
    private long id;

    private String name;
}

@DiscriminatorValue("RECTANGLE")
@Entity
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Rectangle extends Shape {
    @OneToMany(mappedBy = "rectangle", fetch = FetchType.LAZY)
    private Set<Sides>;
}

@DiscriminatorValue("RECTANGLE")
@Entity
@Getter
@Setter
@AllArgsConstructor
@NoArgsConstructor
public class Rectangle extends Shape {
    @OneToMany(mappedBy = "rectangle", fetch = FetchType.LAZY)
    private Set<Sides>;
}

16 Replies

JavaBot•7d ago

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dan1st•7d ago

Can you use a LEFT JOIN? something like SELECT FROM Shape s LEFT JOIN FETCH s.vertices ve LEFT JOIN FETCH s.angles an LEFT JOIN FETCH s.sides si

ayylmao123xddOP•7d ago

probably what in the case where i cant edit the repository but i want to add another class like a circle maybe but i cant change the repositorys code (stupid requirements)

dan1st•7d ago

if you really want to, you could generate the code

ayylmao123xddOP•7d ago

hmmmmmmm

dan1st•7d ago

but you probably don't want to (at build time)

ayylmao123xddOP•7d ago

ye that would need entity manager

dan1st•7d ago

or make a custom repository I meant generating the repository interface at compile-time

ayylmao123xddOP•7d ago

yea that too my idea was to make a strategy for each class and basically loop over them all