How to implement an entity containing two lists of entities of the same type in Spring Data

Question

I have entity Order. It contains a list of glass parts and a list of non-glass parts. Part is a single entity with attribute PartType (glass/non-glass). Is this please doable with Spring Data? How? I'm using Spring Boot 1.3.1.RELEASE with Hibernate.

@Entity
@Table(name="order")
public class Order {

    ...

    @OneToMany(...)
    private List<Part> glassParts;

    @OneToMany(...)
    private List<Part> otherParts;
}

@Entity
@Table(name="part")
public class Part {

  ...

  @Column(...)
  private PartType partType;

  @Column(...)
  private String code;

  @Column(...)
  private String description;
}

Answer 1

I believe that in you case it is not a good idea to create two lists. To achive the result there are two common approaches. The first one is to create a bi-directional relation and implement a Repository and Manager layers with an appropriate conditions:

@Entity
@Table(name="order")
public class Order {

    ...

    @OneToMany(mappedBy = "order", fetch = FetchType.LAZY, cascade = { ... })
    private List<Part> parts;
}

@Entity
@Table(name="part")
public class Part {

  ...

  @JoinColumn(name = "r_order_id", referencedColumnName = "id")
  @ManyToOne(...)  
  private Order order;
  @Column(...)
  private PartType partType;

  @Column(...)
  private String code;

  @Column(...)
  private String description;
}

public interface PartInterface implements CrudRepository<Part, Long> {

  List<Part> findByOrderIdAndPartType(Long orderId, PartType partType);
}

@Component
public class PartManager {

  @Autowired
  private PartInterface partInterface;

  public List<Part> getGlassPartsByOrderId(Long orderId) {
    return List<Part> partInterface.findByOrderIdAndPartType(orderId, PartType.GLASS);
  }

  public List<Part> getNonGlassPartsByOrderId(Long orderId) {
    return List<Part> partInterface.findByOrderIdAndPartType(orderId, PartType.NON_GLASS);
  }
}

The second one is to filter all the parts of the order by the type:

public interface OrderInterface implements CrudRepository<Order, Long> {

  @Override
  Order findOne(Long orderId);
}

@Component
public class OrderManager {

  @Autowired
  private OrderInterface orderInterface;

  public List<Part> getGlassPartsByOrderId(Long orderId) {    
    return getOrderParts(orderId).stream().filter(part -> Objects.equals(PartType.GLASS, part.getPartType())).collect(Collectors.toList());    
  }

  public List<Part> getNonGlassPartsByOrderId(Long orderId) {
    return getOrderParts(orderId).stream().filter(part -> Objects.equals(PartType.NON_GLASS, part.getPartType())).collect(Collectors.toList());    
  }

  private List<Part> getOrderParts(Long orderId) {
    Order order = orderInterface.findOne(Long orderId);
    if (Objects.isNull(order) || Objects.isNull(order.getParts())) {
      return Collections.emptyList();
    } else {
      return order.getParts();
    }
  }
}

Actually there is another one option - to filter parts inside the entity on the fly:

@Entity
@Table(name="order")
public class Order {

    @OneToMany(...)
    private List<Part> parts;

    public List<Part> getGlassParts{
      if (Objects.nonNull(parts)) {
        return parts.stream().filter(part -> Objects.equals(PartType.GLASS, part.getPartType())).collect(Collectors.toList());
      } else {
        return Collections.emptyList();
      }
    }

    public List<Part> getNonGlassParts{
      if (Objects.nonNull(parts)) {
        return parts.stream().filter(part -> Objects.equals(PartType.NON_GLASS, part.getPartType())).collect(Collectors.toList());
      } else {
        return Collections.emptyList();
      }
    }
}

UPDATE Since you're using Hibernate there is an ORM-dependent option to get the desired result it's a @JoinColumnOrFormula annotation that is available for Hibernate only:

@Entity
@Table(name="order")
public class Order {

    @OneToMany(...)
    @JoinColumnOrFormula(
      column = @JoinColumn(name = "id", referencedColumnName = "r_order_id", insertable = false, updatable = false)
      ,formula = @JoinFormula(value = PartType.GLASS_STR_VALUE, referencedColumnName = "partType"))
    private List<Part> glassParts;

    @OneToMany(...)
    @JoinColumnOrFormula(
      column = @JoinColumn(name = "id", referencedColumnName = "r_order_id", insertable = false, updatable = false)
      ,formula = @JoinFormula(value = PartType.NON_GLASS_STR_VALUE, referencedColumnName = "partType"))
    private List<Part> nonGlassParts;    
}

Please pay your attention that the value parameter inside the @JoinFormula clause must be a String