photo matt wrote:
My two models are ProductType and Product. ProductType has_many Products.
ProductType.destroy should fail and set an error if products.count > 0.
Before I re-invent the wheel, there must be some rails way of approaching this problem. Any thoughts?
If you've (1) included belongs_to ProductType in your Products model, and (2) included ProductType_id as a foreign key in your Products table, then what you're looking for is the default behavior.
hth, Bill
Hi Matt,
photo matt wrote:
First, thank you for signing your post. Maybe I'm just getting old but I like to know with whom I'm conversing.
my application is not working like that.
Then it's broke. But then you already knew that 
I'll apologize up front for the shortness of my response. I don't have much time at the moment and hope you won't be offended.
Here's what I'd do if I had 20 minutes and your code. It's what I _always_ do when I'm going to try something new or having a problem.
Do NOT use any of the Rails magic you don't absolutely have to except for scaffolding. The scaffold code works. Always. Unless you've screwed up something it depends on. And that's what you need to find out. If you're using migrations, don't for this. Because that might be where you're problem is. Use a script. Same principle applies across the board. Focus on what you're trying to discover and don't include ANYTHING that might obscure that.
1) Set up a database named 'sandbox' (if you don't already have one) 2) Create the tables you need to investigate the thing you're interested in. In your case you need two tables. Use the same convention you're already using. Other than pluralization, Rails doesn't give a damn whether you use underscores / CamelCase or not. Use the scaffolding to learn. The product_types table should only have two fields: id and a text field named whatever you've got it named in the app you're having a problem with. The products table should only have three fields: id, product_type_id, and a text field. 3) Scaffold your sandbox app on both the product and product_type models. 4) Add the relations to your models. 5) Add a product type 6) Add a product 7) Try to delete the product type. You should get an error. If you don't, the problem's in your setup / config. If you do, the problem's in your (other) code.
I'm sorry I can't offer more right now. I'll be back in 8-10 hours. Let us know how it goes.
Best regards, Bill
Hi Matt,
photo matt wrote:
I managed to reproduce the same behavior in a sandbox.
Excellent! Please post your sandbox code. Including your SQL script.
I've also searched the documentation and I can't seem to find where it says that this is the default behavior.
Not surprising. It's an implied understanding about the way databases work You may well have discovered and reported a bug!
Good on ya, bud! And even if it's not a bug, we'll all learn something.
Best regards, Bill
photo matt wrote:
Unfortunately, Rails migrations don't provide a database-independent way to specify these foreign key constraints, so we had to resort to executing native DDL statements (in this case, those of MySQL)."
Which is precisely why I said, in my earlier response:
If you're using migrations, don't for this. Because that might be where you're problem is. Use a script.
" Do I contradict myself? Very well, then I contradict myself, I am large, I contain multitudes. " Walt Whitman
Congrats on your learning, though. Good post. You've undoubtedly helped someone who will follow your footsteps. I hope you see that as a Good Thing.
Best regards, Bill
" Do I contradict myself? Very well, then I contradict myself, I am large, I contain multitudes. " Walt Whitman
The allusion was to Rails.