Foreign key constraint fails while using Spring Data - mysql

Question

I'm using Spring Data to access my MySQL database with following entities
#Entity
#Table(name = "tbl_product")
public class Product implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY) private Long id;
#ManyToOne(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
#JoinColumn
private Category category;
}
#Entity
#Table(name = "tbl_category")
public class Category implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(unique = true)
private String name;
}
Now I try to use my Controller to delete Product
#RequestMapping(path="/remove/{id}", method=RequestMethod.DELETE)
#ResponseBody
public String removeProduct(#PathVariable Long id) {
return productService.removeProduct(id);
}
public String removeProduct(Long productID) {
try {
productRepository.delete(productID);
return "OK";
} catch (Exception e) {
logger.info(e.getMessage());
return "Error";
}
}
Now, for example if there are 3 Products with Category A and 1 with Category B, I can remove the one with Category B. But if I try to remove any other one, I got
Cannot delete or update a parent row: a foreign key constraint fails
(product_db.tbl_product, CONSTRAINT FKfq7110lh85cseoy13cgni7pet
FOREIGN KEY (category_id) REFERENCES tbl_category (id))

Answer 1

It is because of the cascading that you are applying by cascade = CascadeType.ALL.
So, whenever you delete any product, JPA deletes the category id too. It works well if that category is not associated with any other product(which is what is happening in your second case). But if the category is associated with any other product then the foreign key constraint fails stating that category which you are trying to delete is associated with other product.
You should be very careful while mentioning cascade type. By default cascade mode is NONE but you can give different strategies like UPDATE, PERSIST etc. based upon your requirement