Updating foreign key

For some common errors and how to solve them, see Errors and Workarounds.In the previous tutorial you displayed related data; in this tutorial you'll update related data.

SET FOREINGN KEY_CHEKS = 1;or instead ' REPLACE INTO..' use only ' UPDATE...' and INSERT INTO when necessary.The Contoso University sample web application demonstrates how to create ASP.NET MVC 4 applications using the Entity Framework 5 Code First and Visual Studio 2012.Entity Framework figures out that this time it is the navigation property that has changed and updates accordingly. How will Entity Framework handle the inconsistency? Having tested three cases so far, this post could end here with Entity Framework having passed the tests. I’ll update both to new values, but to point to different objects. That’s also great, aborting is the only reasonable alternative in this place.In earlier My SQL releases, foreign key metadata, which is owned by the child table, could not be updated safely. In that case, the (child table) row containing such a foreign key is permitted to be inserted, and does not match any row in the referenced (parent) table.It is possible to implement other semantics using triggers.Otherwise, My SQL implicitly creates a foreign key index that is named according to the following rules: CREATE TABLE parent ( id INT NOT NULL, PRIMARY KEY (id) ) ENGINE=INNODB; CREATE TABLE child ( id INT, parent_id INT, INDEX par_ind (parent_id), FOREIGN KEY (parent_id) REFERENCES parent(id) ON DELETE CASCADE ) ENGINE=INNODB; CREATE TABLE product ( category INT NOT NULL, id INT NOT NULL, price DECIMAL, PRIMARY KEY(category, id) ) ENGINE=INNODB; CREATE TABLE customer ( id INT NOT NULL, PRIMARY KEY (id) ) ENGINE=INNODB; CREATE TABLE product_order ( no INT NOT NULL AUTO_INCREMENT, product_category INT NOT NULL, product_id INT NOT NULL, customer_id INT NOT NULL, PRIMARY KEY(no), INDEX (product_category, product_id), INDEX (customer_id), FOREIGN KEY (product_category, product_id) REFERENCES product(category, id) ON UPDATE CASCADE ON DELETE RESTRICT, FOREIGN KEY (customer_id) REFERENCES customer(id) ) ENGINE=INNODB; SHOW CREATE TABLE ibtest11c\G *************************** 1.row *************************** Table: ibtest11c Create Table: CREATE TABLE `ibtest11c` ( `A` int(11) NOT NULL auto_increment, `D` int(11) NOT NULL default '0', `B` varchar(200) NOT NULL default '', `C` varchar(175) default NULL, PRIMARY KEY (`A`,`D`,`B`), KEY `B` (`B`,`C`), KEY `C` (`C`), CONSTRAINT `0_38775` FOREIGN KEY (`A`, `D`) REFERENCES `ibtest11a` (`A`, `D`) ON DELETE CASCADE ON UPDATE CASCADE, CONSTRAINT `0_38776` FOREIGN KEY (`B`, `C`) REFERENCES `ibtest11a` (`B`, `C`) ON DELETE CASCADE ON UPDATE CASCADE ) ENGINE=INNODB CHARSET=utf8mb4 1 row in set (0.01 sec) mysql.Extending metadata locks prevents conflicting DML and DDL operations from executing concurrently on related tables.This feature also enables updates to foreign key metadata when a parent table is modified.

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