active record newbie here

[Snowbird122]

I have 2 tables: Products and ProductLines

Products:
id
product_line_id

ProductLines:
id
product_line


Product Model:

     class Product < ActiveRecord::Base
       belongs_to :product_line
     end

ProductLine Model:

     class ProductLine < ActiveRecord::Base
       has_one :product
     end

In my listing code, I am trying to show the product line for each product like this:

     <% for product in @products %>
       <tr><td><%=h product.product_line %></td></tr>
    <% end %>

I am getting this error:
DBI: DatabaseError: Execute
OLE error code:80040E37 in Microsoft OLE DB Provider for SQL Server
Invalid object name 'product_lines'.
HRESULT error code:0x80020009
Exception occurred.: SELECT TOP 1 * FROM product_lines WHERE (product_lines.id = 4)


Note that it thinks my table is named 'product_lines' when it is really named ProductLines. Also note that I am using MS SQL Server, which should be fine, but is noteworthy.

[Snowbird122]

I changed my ProductLine model to

 class ProductLine < ActiveRecord::Base
   has_many :products
 end

but still get the same error.

[Luke Redpath]

Your table names should be product_lines and products, lowercase with underscores, not camel case. That is the Rails convention. If you really want to keep it as it is, then you need to set the table name in each of your models. E.g.

class ProductLine < AR::Base
  set_table_name 'ProductLines'
end

I'd recommend sticking with Rails conventions unless you are forced to do otherwise (for example, working with legacy databases).

[Snowbird122]

Thanks Luke. I changed my table names to products and product_lines, and now I'm not getting the error, but instead, I get a # for allmy product_lines. Any ideas on that?

[vgarcia]

Is the product_line field in your database table a number? You'll probably have to write code to reference another field in your product_line table as the one to display to the user.

[Snowbird122]

Thanks Vinnie. The product line field in the table product_lines is nvarchar(50), so it isn't a number. In the view, I even tried product.product_line.to_s, but I still get the # for every row.

[Luke Redpath]

Can you post your schema?

[samsm]

Thanks Vinnie. The product line field in the table product_lines is nvarchar(50), so it isn't a number. In the view, I even tried product.product_line.to_s, but I still get the # for every row.

I think the confusion is that the product_line you are using is an Active Record derived ProductLine object, not just the product_line field in your database.

Try:
product.product_line.product_line to get at that value.

If that works, you can add a custom to_s method in the ProductLine class, so that what you were initially trying will work.

     class ProductLine < ActiveRecord::Base
       has_one :product
       def to_s
         self.product_line
       end
     end

Then you could use products.product_line and maybe get what you want.

[Eric.Coleman]

To add to this, I've been playing with rails a bit lately and don't really get how to do relationship mapping with active record. I can't seem to find a decent tutorial that I can wrap my head around it. Maybe im just tring to hard.

Anyone have a good page or tutorial or something available that points out how to handle relationships? I'd be really greatful

Thanks,
Eric

[Luke Redpath]

This pretty much sums it up:

http://api.rubyonrails.com/classes/A...ssMethods.html

[Snowbird122]

samsm: That was exactly the problem. When I changed it to product.product_line.product_line, it worked. When I added the to_s function, and changed it back to product.product_line, that worked also.

I don't really understand why I had this problem. Can you point me to a resource that explains this?

Luke - thanks for your help also.

[Fenrir2]

Because:

product.product_line

Returns the ProductLine associated with the Product. So it delivers an object that represents a row in the database. If you do:

pl = ProductLine.find(1)
pl.product_line

pl represents a row in the DB too. If you do pl.product_line, that returns the value of a column of the row: the value of the column product_line in the database.

So if you do:

product.product_line.product_line

The first product_line gets you a row, and the second returns a column of that row.

[Luke Redpath]

It might make it clearer if you were to explain what the product_line column holds as I'm sure there must be a better name for it seeing as your model/table is already called product_line.

[Snowbird122]

Fenrir2: I understand, thanks.

Luke: product_line is the same thing as a category. It is a way to group products. How would you have named the table/field/model differently?

[vgarcia]

Fenrir2: I understand, thanks.

Luke: product_line is the same thing as a category. It is a way to group products. How would you have named the table/field/model differently?

If your current product_line column in your products table references an ID in the product_lines table, then according to the Rails conventions it should be called product_line_id. That way you don't get confusion like the above

[Snowbird122]

Vinnie: See my very first post. That is exactly how I did it.

[samsm]

I'm limited, I always seem to stumble back to the same two words when I'm naming fields. "name" and "description". In fact I'm about a few days from starting a thread asking for advice on better names. Who knows, maybe "name" and "description" are fine. They are probably less ambiguous in templates than what you have.

<% for product in products %>
  <%= product.name %>
  <%= product.description %>
  <%= product.product_line.name %>
  <%= product.product_line.description %>

and don't forget that you can...

  <%= debug product %>
  <%= debug product.methods %>
  <%= debug product.product_line %>
  <%= debug product.product_line.methods %>

... to get an idea of what data and methods 
are available to you with an object.
<% end %>