Spring Data, MySQL and not working unique value - mysql

Question

I'm having troubles getting into Spring Data
I got entity Product which has Category (I'm guessing relation type is right? Product has one Category, Category has many products)
#Entity
public class Product implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
#ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinColumn(name = "category_id")
private Category category;
}
#Entity
class Category implements Serializable {
public Category() {
}
public Category(String name){
this.name = name;
}
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "category_id")
private Long id;
#Column(unique = true)
private String name;
#OneToMany(mappedBy = "category", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private Set<Product> products;
}
Now I try to add new Product via Postman, calling my RestController
#PostMapping("/add")
public Product addProduct(#Valid #RequestBody Product product){
return repository.save(product);
}
With 2 following requests
{
"name" : "pork",
"category" : "meat"
}
{
"name" : "chicken",
"category" : "meat"
}
In the result I got 2 following responses
{
"id": 1,
"name": "pork",
"category": {
"id": 1,
"name": "meat",
"products": null
}
}
{
"id": 2,
"name": "chicken",
"category": {
"id": 2,
"name": "meat",
"products": null
}
}
And on database I actually got 2 categories named "meat" (even tho it should be unique. What's more, do I actually need Set<Product> in my Category class? TBH, Category has no intrest in that at all.

Answer 1

There are a few problems with your code.
You are directly using entity as the rest API model. Suggest to create a separate ProductModel with only fields that client has access to.
You mixing category creation together inside product creation, but your category in the request only contains name. To the backend, unless you check whether such a category exists, it's always treated as a new category.
Before you call repository.save, you need let category knows what's the product inside. In your current code, only product know its category.

Answer 2

You don't need Set products in your Category class (and it's recommended to use only #ManyToOne).