# Agile Rails book: depot problem **URL:** \ **Category:** Rails\ **Created:** [February 5, 2006, 11:49am UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240 "2006-02-05T11:49:52Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 11:49am UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/1 "2006-02-05T11:49:52Z")
I recently finished the first part of the “Agile Rails” book. But, the depot doesn’t completely work as it should. I still have 2 problems: I will explain them in 2 threads. The first one is: I can’t destroy products (I can only creat and update them). When I try to delete a product → [http://localhost:3001/admin/destroy/3](http://localhost:3001/admin/destroy/3) I get this error message: ActiveRecord::StatementInvalid in Admin#destroy Mysql::Error: #23000Cannot delete or update a parent row: a foreign key constraint fails (`depot_development/line_items`, CONSTRAINT `fk_items_product` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`)): DELETE FROM products WHERE id = 3 Can someone explain me what’s going wrong? I’m not a MySQL expert… Before I started to use Rails, I didn’t even know what a foreign key was… Thanks! Johan. ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 2:44pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/2 "2006-02-05T14:44:30Z")
My product Model doesn’t have a relation. However, my line\_item Model does have these relations: > belongs\_to :product > belongs\_to :order So, I thought I should add > has\_many :line\_items to my product Model, but I didn’t work… I still get: > ActiveRecord::StatementInvalid in Admin#destroy > Mysql::Error: #23000Cannot delete or update a parent row: > a foreign key constraint fails (`depot_development/line_items`, > CONSTRAINT `fk_items_product` FOREIGN KEY (`product_id`) > REFERENCES `products` (`id`)): DELETE FROM \>products WHERE id = 4 ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 2:10pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/3 "2006-02-05T14:10:24Z")
> ActiveRecord::StatementInvalid in Admin#destroy > Mysql::Error: #23000Cannot delete or update a parent row: a foreign key > constraint fails (`depot_development/line_items`, CONSTRAINT > `fk_items_product` FOREIGN KEY (`product_id`) REFERENCES `products` > (`id`)): DELETE FROM products > WHERE id = 3 How does your product Model look like? Is there a relation to line\_items? Beate ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 3:27pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/4 "2006-02-05T15:27:14Z")
Well, I did add it 🙂 It didn’t fix the problem, but everything works now (with “has\_many :line\_items” in the product model…) My problem had to do with my MySQL line\_items database. Apparantly, I had to tell the database to CASCADE on delete. With that done, everything works fine. Here is where I found the solution: [http://dev.mysql.com/doc/refman/5.0/en/innodb-foreign-key-constraints.html](http://dev.mysql.com/doc/refman/5.0/en/innodb-foreign-key-constraints.html) > CASCADE: Delete or update the row from the parent table and automatically delete \>or update the matching rows in the child table. Both ON DELETE CASCADE and ON \>UPDATE CASCADE are supported. Between two tables, you should not define several \>ON UPDATE CASCADE clauses that act on the same column in the parent table or in \>the child table. Before, I used NO ACTION > NO ACTION: In standard SQL, NO ACTION means no action in the sense that an \>attempt to delete or update a primary key value is not allowed to proceed if \>there is a related foreign key value in the referenced table. InnoDB rejects \>the delete or update operation for the parent table. ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 4:41pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/5 "2006-02-05T16:41:21Z")
You could do this, of couse, but it would be better to say rails to do this. I also think that this is not the “state of art”, or do you want to delete orders, when you delete a product? I managed this by putting the main infos of the product in line\_items, i.e. articlenumber, title, price. So I can delete products again. I can give you an example: When I delete an order, the belonging line\_items should be removed. So this is what I have in my order model: has\_many :line\_items, :dependent =\> true This workes 😉 Beate ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 7:17pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/6 "2006-02-05T19:17:22Z")
Did you duplicate the price, title, … then? Do you have a products table with price, title,… and a line\_items table that doesn’t reference the products table, but stores the price, title,… by itself? That way your DB tables don’t rely on each other? I guess that’s a way to do it… I agree that my code isn’t state of the art… However, I would like to use the delete cascade rule… I think it makes sense to delete orders that rely on a product you can’t ship anymore. But then, the code should be adapted, so you can notify people who ordered such a product. I have to say, this relational DB stuff isn’t my favorite part of RoR. I don’t know enough about it yet. Maybe I should read about MySQL. Johan. ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 3:13pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/7 "2006-02-05T15:13:48Z")
2006/2/5, Johan Van M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > My product Model doesn’t have a relation. > > However, my line\_item Model does have these relations: > > > belongs\_to :product > > belongs\_to :order > > So, I thought I should add > > > has\_many :line\_items no, don’t 😉 Who does your controller look like? Beate ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 8:19pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/8 "2006-02-05T20:19:05Z")
2006/2/5, Johan Van M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Did you duplicate the price, title, … then? > Do you have a products table with price, title,… > and a line\_items table that doesn’t reference the products table, but > stores the price, title,… by itself? Yes, that’s the way I do it. > That way your DB tables don’t rely on each other? > I guess that’s a way to do it… yes, they don’t rely on each other. > I agree that my code isn’t state of the art… > However, I would like to use the delete cascade rule… > I think it makes sense to delete orders that rely on a product you can’t > ship anymore. But then, the code should be adapted, so you can notify > people who ordered such a product. If a product is deleted, it won’t be displayed in the shop afterwards, and so it can’t be ordered. At least in my shop 😉 > I have to say, this relational DB stuff isn’t my favorite part of RoR. > I don’t know enough about it yet. Maybe I should read about MySQL. You need not to know this much SQL for Rails, but you should understand the ralations: 1:n, 1:1, n:m and how you build them in tables. Then you write your relations in the models, and thats all 😉 Beate ---
**Author:** ![johan-vm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/c77e96/32.png) [@johan-vm](https://www.ruby-forum.com/u/johan-vm)\ **Post date:** [February 5, 2006, 7:24pm UTC](https://www.ruby-forum.com/t/agile-rails-book-depot-problem/101240/9 "2006-02-05T19:24:44Z")
> I agree that my code isn’t state of the art… > However, I would like to use the delete cascade rule… > I think it makes sense to delete orders that rely on a product you can’t > ship anymore. But then, the code should be adapted, so you can notify > people who ordered such a product. Thinking about it, this is a worst case scenario - and not very professional. The product running out of stock should automattically be deleted when the last item has been sold, without deleting the pending order(s). You’re right Beate 🙂