Panache Query/DTO projection with fields from referenced entity

Description

Currently, the Panache project method works great if the parameters in the DTO’s constructor belongs to the same entity.

The case of having a DTO with also fields from referenced entities is not working because the required “dot” notation to build a working query is not compatible with Java naming that doesn’t allow the usage of dots . in a parameter’s name.

Example DogDto based on Person and Dog entities from hibernate-orm-panache integration tests

@Entity
public class Person extends PanacheEntity {

    public String name;
    @Column(unique = true)
    public String uniqueName;

    @OneToMany(mappedBy = "owner", cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    public List<Dog> dogs = new ArrayList<>();
}

@Entity
public class Dog extends PanacheEntityBase {

    @Id
    @GeneratedValue
    public Integer id;

    public String name;

    public String race;

    @ManyToOne
    public Person owner;
}

@RegisterForReflection
public class DogDto {

    public String name;

    public String ownerName;

    public DogDto(String name, String ownerName) {
        this.name = name;
        this.ownerName = ownerName;
    }

}

The DogDto’s constructor parameters have no way to reference the field name from the entity Person

Implementation ideas

The idea is to add a ProjectionForField annotation for ElementType.PARAMETER to let the developers provide the “SQL path” to get the value for the field the annotation refers to in the DTO’s constructor, considering the projection works starting from the DTO’s constructor parameters.

Example based on the above use case

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.PARAMETER)
public @interface ProjectionForField {
    String value();
}

@RegisterForReflection
public class DogDto {

    public String name;

    public String ownerName;

    public DogDto(String name, @ProjectionForField("owner.name") String ownerName) {
        this.name = name;
        this.ownerName = ownerName;
    }

}

The annotation’s name ProjectionForField wants to be consistent with the annotation ProjectionFor (available for Panache Mongo extension) that refers to classes.

[loicmathieu]

@anthony-quiros please open a different github issue for your example, did you try your example ? Which exception did it throws ?

[FroMage]

That feature sounds very reasonable.