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How to retrieve data from parent-child tables using Spring Data JPA?

In my Spring Boot app, I use Hibernate and applied the necessary relations to the following entities properly.
#Entity
public class Recipe {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(nullable=false, length=50)
private String title;
#OneToMany(mappedBy = "recipe", cascade = CascadeType.ALL)
private List<RecipeIngredient> recipeIngredients = new ArrayList<>();
}
#Entity
public class RecipeIngredient {
#EmbeddedId
private RecipeIngredientId recipeIngredientId = new RecipeIngredientId();
#ManyToOne(optional = true, fetch = FetchType.LAZY)
#MapsId("recipeId")
#JoinColumn(name = "recipe_id", referencedColumnName = "id")
private Recipe recipe;
#ManyToOne(optional = true, fetch = FetchType.LAZY)
#MapsId("ingredientId")
#JoinColumn(name = "ingredient_id", referencedColumnName = "id")
private Ingredient ingredient;
}
#Entity
public class Ingredient
{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(unique=true, nullable=false, length=50)
#EqualsAndHashCode.Include
private String name;
#OneToMany(mappedBy = "ingredient", cascade = CascadeType.ALL)
private Set<RecipeIngredient> recipeIngredients = new HashSet<>();
}
Now I am trying to retrieve data by merging related entities. For example, when retrieving a Recipe, I also need to retrieve all Ingredients belonging to this Recipe.
As far as I know, I can use Projection and maybe it is better to only use Hibernate features and retrieve related table data via Java Stream. I have no idea how should I retrieve data via Hibernate.
Suppose that I just need an Optional<Recipe> that has List<Ingredient>. Then, I probably need a DTO class something like that:
#Data
public class ResponseDTO {
private Long id;
private String title;
List<RecipeIngredient> ingredients;
// getter, setter, constructor
}
So, how should I populate this DTO with the requested Recipe and corresponding Ingredient data (getting Ingredient names besides id values) using Java Stream?
Or if you suggest Projection way, I tried it but the data is multiplied by the ingredient count belonging to the searched recipe.
Update:
#Getter
#Setter
#NoArgsConstructor
public class ResponseDTO {
private Long id;
private String title;
List<IngredientDTO> ingredientDTOList;
public ResponseDTO(Recipe recipe) {
this.id = recipe.getId();
this.title = recipe.getTitle();
this.ingredientDTOList = recipe.getRecipeIngredients().stream()
.map(ri -> new IngredientDTO(ri.getIngredient().getName()))
.toList();
}
}
#Getter
#Setter
public class IngredientDTO {
private Long id;
private String name;
public IngredientDTO(String name) {
this.name = name;
}
}

First, in the ResponseDTO you will need you change the type of ingredients from List<RecipeIngredient> to List<Ingredient>.
To manually perform the mapping, you should use (to map from a suppose Recipe recipe to a RespondeDTO response):
ResponseDTO recipeToResponseDTO(Recipe recipe) {
ResponseDTO response = new ResponseDTO();
response.setId(recipe.getId());
response.setTitle(recipe.getTitle());
response.setIngredients(recipe.recipeIngredients.stream()
.map(RecipeIngredient::getIngredient()
.collect(Collectors.toList());
return response;
}
On the other hand, to model a n-n relation, I encourage you to use the approach proposed by E-Riz in the comment.

JPA one to one mapping creates multiple query when child entity is not found

I have a parent entity 'contracts' that has a one-to-one relation with another entity 'child-contract'. the interesting thing is that the mapping field ('contract_number')id not a primary key-foreign key but is rather a unique field in both the tables. Also it is possible for a contracts to not have any child contract altogether. With this configuration I have observed hibernate to generate 1 additional query every time a contracts does not have a child-contract. I filed this behavior very strange. Is there a way to stop these unnecessary query generation or have I got something wrong.
below is a piece of my code configuration.
#Data
#Entity
#Table(name = "contracts")
public class Contracts implements Serializable {
#Id
#JsonIgnore
#Column(name = "id")
private String id;
#JsonProperty("contract_number")
#Column(name = "contract_number")
private String contractNumber;
#OneToOne(fetch=FetchType.EAGER)
#Fetch(FetchMode.JOIN)
#JsonProperty("crm_contracts")
#JoinColumn(name = "contract_number", referencedColumnName = "contract_number")
private ChildContract childContract ;
}
#Data
#NoArgsConstructor
#Entity
#Table(name = "child_contract")
#BatchSize(size=1000)
public class ChildContract implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#JsonProperty("id")
#Column(name = "id")
private String id;
#JsonProperty("contract_number")
#Column(name = "contract_number")
private String contractNumber;
}
Please help.
Thank-you

You can use NamedEntityGraph to solve multiple query problem.
#NamedEntityGraph(name = "graph.Contracts.CRMContracts", attributeNodes = {
#NamedAttributeNode(value = "crmContract") })
Use this on your repository method as
#EntityGraph(value = "graph.Contracts.CRMContracts", type = EntityGraphType.FETCH)
// Your repo method in repository

Clone object without ids using mapstruct

I have an object which contains several list. is there a method to clone this object without id using mapstruct even for the nested object list in an automatic way to be able to persist it.
#Data
public class ParentDto {
#Id
private Long id;
private String name;
private List<Child1Dto> children1;
private List<Child1Dto> children2;
}
#Data
public class Child1Dto {
#Id
private Long id;
private String name;
}
#Data
public class Child2Dto {
#Id
private Long id;
private String name;
}
Actual mapper
#Mapper(mappingControl = DeepClone.class)
public interface CloneParentMapper {
#Mapping(target = "id", ignore = true)
ParentDto cloneWithoutId(ParentDto parentDto );
#Mapping(target = "id", ignore = true)
Child1Dto cloneWithoutId(Child1Dto child1Dto );
#Mapping(target = "id", ignore = true)
Child2Dto cloneWithoutId(Child2Dto child2Dto );
}
is there a way to ignore all id without doing #Mapping(target = "id", ignore = true) on every list?

I really feel this is the best and easiest way to ignore fields.
But still if u wanna ignore fields and not mark them as ignored specifically, then you can use constructors based mappings and have a separate constructor without id field. You will have to mark this constructor as #Default.
https://mapstruct.org/documentation/stable/reference/html/#mapping-with-constructors

How to get object from OneToMany collection of objects?

I have an Order entity and OrderProduct. I want to show order details on frontend and of course order products in it. So how to fetch product object in OrderProduct JSON. I'm missing product object in products array. I don't need order object one more time and i think it going to be a infinite recursion stuff with it. :)
My Order entity:
#Entity
#Getter
#Setter
#Table(name ="orders")
public class Order{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
public Long id;
private BigDecimal totalPrice;
#OneToMany(mappedBy = "order", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JsonManagedReference(value="orders")
private List<OrderProduct> products = new ArrayList<>();
private int userId;
#DateTimeFormat(pattern="dd/MM/yyyy")
private Date date = new Date();
#DateTimeFormat(pattern="dd/MM/yyyy")
private Date deliveryDate;
#Enumerated(EnumType.STRING)
private OrderType orderType;
}
My OrderProduct entity:
#Entity
#Setter
#Getter
public class OrderProduct {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#ManyToOne(fetch = FetchType.EAGER)
#JsonBackReference(value="product")
#JoinColumn(name = "product_id")
private Product product;
#ManyToOne
#JsonBackReference(value="orders")
#JoinColumn(name = "order_id")
private Order order;
private Integer quantity;
}
Product entity:
#Entity
#Getter
#Setter
public class Product {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(unique = true)
private String name;
private double price;
#OneToMany(mappedBy = "product", cascade = CascadeType.ALL)
#JsonManagedReference(value="ingredients")
private List<Ingredient> ingredients = new ArrayList<>();
#OneToMany(mappedBy = "product",fetch = FetchType.EAGER)
#JsonManagedReference(value="product")
private List<OrderProduct> products = new ArrayList<>();
private String fileName;
}

This can help annotate one of your entity clases with
#JsonIdentityInfo(
property = "id",
generator = ObjectIdGenerators.PropertyGenerator.class
)
Every time when JSON serialization go in circles object data will be replaced with object id or orher field of entity for your choose.

You can use #JsonViewannotation to define the fields that you need to serialize to JSON
How it works:
You need define class with interfaces. For example:
public class SomeView {
public interface id {}
public interface CoreData extends id {}
public interface FullData extends CoreData {}
}
Mark entity fields with #JsonView(<some interface.class>)
public class User {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#JsonView(SomeView.id.class)
private Long id;
#Column(nullable = false)
#JsonView(SomeView.CoreData.class)
private String username;
#Column(nullable = false)
#JsonView(SomeView.FullData.class)
private String email;
}
Annotate endpoint with #JsonView(<some interface.class>)
#GetMapping()
#JsonView(<some interface.class>)
public User getUser() {
return <get user entity somwhere>
}
In case #JsonView(SomeView.id.class) you will get this JSON:
{
id: <some id>
}
In case #JsonView(SomeView.CoreData.class):
{
id: <some id>,
username: <some username>
}
In case #JsonView(SomeView.FullData.class):
{
id: <some id>,
username: <some username>,
email: <some email>
}
#JsonView also works with embeded objects and you can annotate one field with multiply views classes - #JsonView({SomeView.FullData.class, SomeOtherView.OtherData.class})
In your case i think you should annotate all the fields you need except:
#OneToMany(mappedBy = "product",fetch = FetchType.EAGER)
#JsonManagedReference(value="product")
private List<OrderProduct> products = new ArrayList<>();
in Product
to avoid circular serialization
Or as alternative you can just use DTO classes or seralize oject to JSON manualy (https://thepracticaldeveloper.com/java-and-json-jackson-serialization-with-objectmapper/)

This can be done by my library beanknife
// This configure generate a class named ProductInfo which has the same shape with Product without property "products"
#ViewOf(value = Product.class, genName="ProductInfo", includePattern = ".*", excludes = {"products"})
class ProductInfoConfigure {}
// This configure generate a class named OrderProductRelation with the same shape of OrderProduct.
// But it has not order property and the type of its product property is change to ProductInfo generated above.
#ViewOf(value = OrderProduct.class, genName="OrderProductRelation", includePattern = ".*", excludes = {"order"})
class OrderProductRelationConfigure {
#OverrideViewProperty("product")
private ProductInfo product;
}
// This configure generate a class named OrderDetail with the same shape of Order.
// But the type of its products property is change to List<OrderProductRelation>
#ViewOf(value = Order.class, genName="OrderDetail", includePattern = ".*")
class OrderDetailConfigure {
#OverrideViewProperty("products")
private List<OrderProductRelation> products;
}
will generate these classes:
class ProductInfo {
private Long id;
private String name;
private double price;
private List<Ingredient> ingredients; // it is not processed because you have not provide the class Ingredient
private String fileName;
}
public class OrderProductRelation {
private Long id;
private ProductInfo product;
private Integer quantity;
}
public class OrderDetail {
public Long id;
private BigDecimal totalPrice;
private List<OrderProductRelation> products;
private int userId;
private Date date = new Date();
private Date deliveryDate;
private OrderType orderType;
}
Then
Order order = ...
OrderDetail orderDetail = OrderDetail.read(order);
// serialize the otherDetail instead of order.
List<Order> orders = ...
List<OrderDetail> orderDetails = OrderDetail.read(orders);
// serialize the orderDetails instead of orders.
Possible problems:
I doesn't use Lombok, so Lombok may need to be adapted because it change the byte code on the fly. But it is not a big problem, I will try to adapt it if someone commit the issue and provide enough use cases.
The generated class does not inherit the annotation on the original class. In next release I will provide a sulotion. At this moment, as a workaround, we can use custom method to convert the property manually. such as
#ViewOf(value = Order.class, genName="OrderDetail", includePattern = ".*")
class OrderDetailConfigure {
#OverrideViewProperty("products")
private List<OrderProductRelation> products;
#OverrideViewProperty("orderType")
public static String orderType(Order source) {
return source.getOrder().name();
}
}
The generated class will be changed to
public class OrderDetail {
public Long id;
private BigDecimal totalPrice;
private List<OrderProductRelation> products;
private int userId;
private Date date = new Date();
private Date deliveryDate;
private String orderType;
}
Update
Version 1.2.0 released. Add support of annotation inheritance.
#ViewOf(value = Order.class, genName="OrderDetail", includePattern = ".*")
#UseAnnotation({DateTimeFormat.class, Enumerated.class, JsonProperty.class})
class OrderDetailConfigure {
#OverrideViewProperty("products")
private List<OrderProductRelation> products;
}
generate
public class OrderDetail {
public Long id;
private BigDecimal totalPrice;
private List<OrderProductRelation> products;
private int userId;
#DateTimeFormat(pattern="dd/MM/yyyy")
private Date date;
#DateTimeFormat(pattern="dd/MM/yyyy")
private Date deliveryDate;
#Enumerated(EnumType.STRING)
private OrderType orderType;
}

How can I convert this 3 JOIN query into a Spring Data JPA named query method?

I am not so into Spring Data JPA and I have the following problem trying to implement a named query (the query defined by the method name).
I have these 3 entity classes:
#Entity
#Table(name = "room_tipology")
public class RoomTipology implements Serializable{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#Column(name = "tipology_name")
private String name;
#Column(name = "tipology_description")
private String description;
#Column(name = "time_stamp")
private Date timeStamp;
#OneToMany(mappedBy = "roomTipology")
private List<Room> rooms;
#OneToOne(mappedBy = "roomTipology")
private RoomRate roomRate;
// GETTER AND SETTER METHODS
}
That represents a tipology of room and that contains this field
#OneToMany(mappedBy = "roomTipology")
private List<Room> rooms;
So it contains the list of room associated to a specific room tipology, so I have this Room entity class:
#Entity
#Table(name = "room")
public class Room implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#ManyToOne
#JoinColumn(name = "id_accomodation_fk", nullable = false)
private Accomodation accomodation;
#ManyToOne
#JoinColumn(name = "id_room_tipology_fk", nullable = false)
private RoomTipology roomTipology;
#Column(name = "room_number")
private String number;
#Column(name = "room_name")
private String name;
#Column(name = "room_description")
#Type(type="text")
private String description;
#Column(name = "max_people")
private Integer maxPeople;
#Column(name = "is_enabled")
private Boolean isEnabled;
// GETTER AND SETTER METHODS
}
Representing a room of an accomodation, it contains this annoted field:
#ManyToOne
#JoinColumn(name = "id_accomodation_fk", nullable = false)
private Accomodation accomodation;
And finally the Accomodation entity class:
#Entity
#Table(name = "accomodation")
public class Accomodation implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id")
private Long id;
#OneToMany(mappedBy = "accomodation")
private List<Room> rooms;
#Column(name = "accomodation_name")
private String name;
#Column(name = "description")
#Type(type="text")
private String description;
// GETTER AND SETTER METHODS
}
Ok, so now I have this Spring Data JPA repository class for RoomTipology:
#Repository
#Transactional(propagation = Propagation.MANDATORY)
public interface RoomTipologyDAO extends JpaRepository<RoomTipology, Long> {
}
Here I want to define a named query method that return to me the list of all the RoomTipology object related to a specific accomodation, I have done it using SQL and it works fine:
SELECT *
FROM room_tipology as rt
JOIN room r
ON rt.id = r.id_room_tipology_fk
JOIN accomodation a
ON r.id_accomodation_fk = a.id
WHERE a.id = 7
But now I want to translate it in a named query method (or at least using HQL)
How can I do it?

Please Try:
#Repository
#Transactional(propagation = Propagation.MANDATORY)
public interface RoomTipologyDAO extends JpaRepository<RoomTipology, Long> {
List<RoomTipology> findByRooms_Accomodation(Accomodation accomodation);
}
The query builder mechanism built into Spring Data repository infrastructure is useful for building constraining queries over entities of the repository. The mechanism strips the prefixes find…By, read…By, query…By, count…By, and get…By from the method and starts parsing the rest of it
At query creation time you already make sure that the parsed property is a property of the managed domain class. However, you can also define constraints by traversing nested properties.
Doc:Here