CODEWITHSUNDEEP
mysqlmany-to-many
kzidane
kzidane

Reputation: 763

Delete from Many to Many Relationship in MySQL

I am not a MySQL professional I am just trying to make simple java application which accesses a MySQL database (e.g. The famous books/authors database) and manipulates it (i.e, add, update, delete).

The problem is that there are two tables that have many to many relationship (e.g. authors table and books table) when I am trying to delete using 

DELETE FROM tableName WHERE someColumnName = 'someValue'

it throws MySQLIntegrityConstraintViolationException with the message "Cannot delete or update a parent row: a foreign key constraint fails"

I know it's because of the "many to many" relationship but actually I don't know what to do with this since I am not a MySQL professional. Any help will be appreciated. Thank you.

Edit: here's the database

DROP DATABASE IF EXISTS books;

CREATE DATABASE books;

USE books;

CREATE TABLE Authors
(
   AuthorID int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   FirstName varchar(30) NOT NULL,
   LastName varchar(30) NOT NULL
)                 ;
CREATE TABLE Titles
(
   ISBN varchar(20) NOT NULL PRIMARY KEY,
   Title varchar(100) NOT NULL,
   EditionNumber int NOT NULL,
   Copyright varchar(4) NOT NULL
)             ;

CREATE TABLE AuthorISBN
(
   AuthorID int NOT NULL,
   ISBN varchar(20) NOT NULL,
   FOREIGN KEY (AuthorID) REFERENCES Authors(AuthorID) ON DELETE SET NULL,
   FOREIGN KEY (ISBN) References Titles(ISBN) ON DELETE SET NULL
)            ;

INSERT INTO Authors (FirstName,LastName) VALUES ('Paul','Deitel')           ;
INSERT INTO Authors (FirstName,LastName) VALUES ('Harvey','Deitel')     ;
INSERT INTO Authors (FirstName,LastName) VALUES ('Abbey','Deitel')     ;
INSERT INTO Authors (FirstName,LastName) VALUES ('Michael','Morgano')    ;
INSERT INTO Authors (FirstName,LastName) VALUES ('Eric','Kern')     ;


INSERT INTO Titles (ISBN,Title,EditionNumber,Copyright) VALUES ('0132152134','Visual Basic 2010 How to Program',5,'2011')          ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (1,'0132152134')     ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (2,'0132152134') ;

INSERT INTO Titles (ISBN,Title,EditionNumber,Copyright) VALUES ('0132151421','Visual C# 2010 How to Program',4,'2011')  ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (1,'0132151421')      ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (2,'0132151421')      ;

INSERT INTO Titles (ISBN,Title,EditionNumber,Copyright) VALUES ('0132575663','Java How to Program',9,'2012')   ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (1,'0132575663')                                               ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (2,'0132575663')                                       ;

INSERT INTO Titles (ISBN,Title,EditionNumber,Copyright) VALUES ('0132662361','C++ How to Program',8,'2012')     ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (1,'0132662361')                                                  ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (2,'0132662361')                                                 ;

INSERT INTO Titles (ISBN,Title,EditionNumber,Copyright) VALUES ('0132404168','C How to Program',6,'2010')     ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (1,'0132404168')                                             ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (2,'0132404168')                                       ;

INSERT INTO Titles (ISBN,Title,EditionNumber,Copyright) VALUES ('013705842X','iPhone for Programmers: An App-Driven Approach',1,'2010')        ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (1,'013705842X')                                                    ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (2,'013705842X')                                                    ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (3,'013705842X')                                                    ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (4,'013705842X')                                                    ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (5,'013705842X')                                                    ;

INSERT INTO Titles (ISBN,Title,EditionNumber,Copyright) VALUES ('0132121360','Android for Programmers: An App-Driven Approach',1,'2012')        ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (1,'0132121360')                                                    ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (2,'0132121360')                                                    ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (3,'0132121360')                                                    ;
INSERT INTO AuthorISBN (AuthorID,ISBN) VALUES (4,'0132121360')                                                    ;

Upvotes: 0

Views: 2860

Answers (1)

A. Cristian Nogueira
A. Cristian Nogueira

Reputation: 735

It is probably because you set your CONSTRAINT onUpdate and onDelete to RESTRICT. You can change it to SET NULL and then be able to delete.

See this section on MySQL documentation.

EDIT

beyond SET NULL, you can try NO ACTION option as well.

IE:

FOREIGN KEY(ord_no,book_id) REFERENCES neworder(ord_no,book_id)  
ON UPDATE SET NULL ON DELETE SET NULL

OR

FOREIGN KEY(ord_no,book_id) REFERENCES neworder(ord_no,book_id)  
ON UPDATE NO ACTION ON DELETE NO ACTION

Hope it helps.

Upvotes: 1

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