Duplicate entry instead of using existing entity - mysql

Question

I'm getting MySQLIntegrityConstraintViolationException while trying to add new Product. Each Product has Category which has unique value name. I'm getting this exception when I try to add new Product with already existing Category. Example below:
POST 1
{
"name" : "apple",
"categoryName" : "fruit"
}
Response
{
"name": "apple",
"categoryName": "fruit",
"kcal": null
}
Post 2:
{
"name" : "banana",
"categoryName" : "fruit"
}
Response:
{
"timestamp": 1533451793052,
"status": 500,
"error": "Internal Server Error",
"exception": "org.springframework.dao.DataIntegrityViolationException",
"message": "could not execute statement; SQL [n/a]; constraint [UK_8f25rdca1qev4kqtyrxwsx0k8]; nested exception is org.hibernate.exception.ConstraintViolationException: could not execute statement",
"path": "/product/add"
}
Which is obviously not what I'd expect, instead I want banana to use same category as apple.
Ok, the code, first entities and dto's
#Entity
#Table(name = "tbl_product")
public class Product implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
private String name;
private Double kcal;
#ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinColumn
private Category category;
}
public class ProductDto {
private String name;
private String categoryName;
private Double kcal;
}
#Entity
#Table(name = "tbl_category")
public class Category implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(unique = true)
private String name;
public Category(){ }
public Category(String name){
this.name = name;
}
}
Post from controller
#PostMapping("/add")
public ProductDto addProduct(#Valid #RequestBody ProductDto productDto){
Product product = productRepository.save(dtoToEntityTranslator.translate(productDto));
return entityToDtoTranslator.translate(product);
}
And pretty straight-forward translators
public class DtoToEntityTranslator {
public Product translate(ProductDto productDto){
Product product = new Product();
product.setName(productDto.getName());
product.setCategory(new Category(productDto.getCategoryName()));
product.setKcal(productDto.getKcal());
return product;
}
}
public class EntityToDtoTranslator {
public ProductDto translate(Product product){
ProductDto productDto = new ProductDto();
productDto.setName(product.getName());
if(product.getCategory() != null) {
productDto.setCategoryName(product.getCategory().getName());
}
productDto.setKcal(product.getKcal());
return productDto;
}
}
Not sure if it's worth mention, my repository for Product
#Repository
public interface ProductRepository extends CrudRepository<Product, Long> {
}

Answer 1

The error is caused by this line
product.setCategory(new Category(productDto.getCategoryName()));
You are tolding Hibernate that this is a new Category because category name is not the Id for Category.
To solve this, you can get the Category with the provided and set to the Category.
Another way is that for existing Category, instead of sending the name to server, you can consider sending the category id.