Why does my repository findAll() method also returns child objects?

Question

I have a Spring project using Spring JPA. I have a table for Brands and Products, and I have mapped them through @ManyToMany like so:

BRAND ENTITY:

@Entity
public class Brand{


@Id
@GeneratedValue(strategy = GenerationType.IDENTITY, generator = 
"brand_seq_gen")
@SequenceGenerator(name = "brand_seq_gen", sequenceName = "ISEQ$$_73370", allocationSize = 1)
@Column(name = "BRAND_ID")
private Long brandId;

@Column(name = "BRAND_NAME")
private String brandName;

@ManyToMany(fetch = FetchType.LAZY, cascade = {
    CascadeType.ALL
})
@JoinTable(
    name = "BRAND_PRODUCT",
    joinColumns = @JoinColumn(name = "BRAND_ID", referencedColumnName = "BRAND_ID"),
    inverseJoinColumns = @JoinColumn(name = "PRODUCT_ID", referencedColumnName = "PRODUCT_ID")
)
private Set<Product> products = new HashSet<>();    

 //CONSTRUCTORS, SETTERS, AND GETTERS
}

PRODUCT ENTITY:

@Entity
public class Product{


@Id
@GeneratedValue(strategy = GenerationType.IDENTITY, generator = "prod_seq_gen")
@SequenceGenerator(name = "prod_seq_gen", sequenceName = "ISEQ$$_73373", allocationSize = 1)
@Column(name = "PRODUCT_ID")
private Long productId;

@Column(name = "TYPE_DESCRIPTION")
private String typeDescription;

public Product() {
}

@ManyToMany(mappedBy = "products", fetch = FetchType.LAZY)
private Set<Brand> brands = new HashSet<>();
//Setters, Getters, and Constructors

and for example, I would only want to get the information of Brand only (BRAND_ID and BRAND_NAME) without getting the products, how would I access only the brand's information? Thank you!

--EDIT 1--

I would like to access ALL brands without accessing the products on each brand. Is that possible? Or do I create another class?

--EDIT 2--

Here is a sample query when using BrandRepository.findall()

[ {
 "brandId" : 1,
  "brandName" : "Electrolux",
  "products" : [ {
    "productId" : 4,
    "typeDescription" : "Refrigerator"
  }, {
    "productId" : 3,
    "typeDescription" : "Washing Machine"
  } ]
}, {
  "brandId" : 2,
  "brandName" : "Midea",
  "products" : [ {
    "productId" : 4,
    "typeDescription" : "Refrigerator"
  }, {
    "productId" : 2,
    "typeDescription" : "Air Conditioner"
  }, {
    "productId" : 3,
    "typeDescription" : "Washing Machine"
  } ]
}, {
  "brandId" : 3,
  "brandName" : "Samsung",
  "products" : [ {
    "productId" : 1,
    "typeDescription" : "TV"
  }, {
    "productId" : 4,
    "typeDescription" : "Refrigerator"
  } ]
}, {
  "brandId" : 4,
  "brandName" : "LG",
  "products" : [ {
    "productId" : 1,
    "typeDescription" : "TV"
  } ]
} ]

What I want should only be the columns brandId and brandName without the products resulting from @ManyToMany relationship.

--Edit 4-- I found out through logging that the database is being queried two times to retrieve both tables which is why I think it might be better to just use @Query and a projection.

Please follow [the Java naming convention](https://www.oracle.com/java/technologies/javase/codeconventions-namingconventions.html) when writing in Java. For method and variable names camelCase is the norm, for classes and interfaces - PascalCase. SNAKE_CASE is used only for static constants and enums. — MartinBG, May 21 '20 at 11:59

score 2 · Answer 1 · answered May 21 '20 at 10:45

2

Use hibernate lazy loading that will fetch only brands, not the child items(products).

Please have a look at this to understand what the lazy loading means.

answered May 21 '20 at 10:45

chirag soni

624
6
18

I'll quickly read on this! Thank you for your time and response. – Viany Manuel May 21 '20 at 10:45
So I use a function to get the Product? – Viany Manuel May 21 '20 at 10:50
1

Did you check properly if you are using fetch type as Lazy then also why products are getting loaded?? – chirag soni May 21 '20 at 10:52
1

I would recomend before writing such a code please have a look at this example: https://www.baeldung.com/hibernate-lazy-eager-loading – chirag soni May 21 '20 at 10:54
I'm probably reading it right, but I'm not fully understanding how to implement it. I'm using a `RestController` in calling the `findAll()` method, does that make a difference? – Viany Manuel May 21 '20 at 11:13
By the way, does the `private Set products = new HashSet<>();` need to have a setter/getter method? – Viany Manuel May 21 '20 at 11:31
1

yes setter is required as spring, and hibernate internally uses setters, and getters for data binding. – chirag soni May 21 '20 at 11:42
1

You can use `RestController`. this controller will by default provide the JSON data back to its caller. – chirag soni May 21 '20 at 11:44

score 2 · Answer 2 · edited Jun 06 '20 at 08:04

2

Make sure to have spring.jpa.open-in-view=false in your application.properties file. If you have it set to true you will end up querying database when you call get method on your entity.

edited Jun 06 '20 at 08:04

marc_s

675,133
158
1,253
1,388

answered May 21 '20 at 11:47

Aleksander Nuszel

170
7

I think this solved the `FetchType.LAZY` problem, but it induced another problem: the server could no longer initialize a collection of role `products` – Viany Manuel May 21 '20 at 11:55
If lazy problem is solved then please use MartinBG solution with projections. https://www.baeldung.com/spring-data-jpa-projections , it should work :) – Aleksander Nuszel May 21 '20 at 12:06

MartinBG · Accepted Answer · 2020-05-22T10:19:44.660

1

The simplest way to fetch just some entity properties is to use projections

Back to your example, you could have a projection interface defined like that:

interface BrandNameAndId {
  Long getId();
  String getBrandName();
}

And a method like this in your Brand's repository:

List<BrandNameAndId > findAllProjectedBy();

edited May 22 '20 at 10:19

answered May 21 '20 at 11:51

MartinBG

1,034
8
13

There seems to be a compilation error upon trying to use `Collection allBrandNameAndId()` method, but I am able to put into the `Collection findByBrandName(String brandName)` into my @Repository – Viany Manuel May 22 '20 at 04:14
I tried using `@Query("SELECT * FROM BRAND_E", nativeQuery = true)` to method `Collection methodName()`, but the output is null. I also tried it to method `Collection methodName()` but the output now includes `products` field of `Brand` entity. – Viany Manuel May 22 '20 at 08:31
@VianyManuel Please use `List findAllProjectedBy();` as repository method name (answer updated) – MartinBG May 22 '20 at 10:20

Why does my repository findAll() method also returns child objects?

3 Answers3