RoR-Sql query

Hi everyone

Consider there are three tables book,money,card in database.

Book has got column names name,price.

Money has got column names price,type.

Card has got column names type,id.

Now based on the ‘id’ of the ‘card’ i’ve to fetch ‘name’ of the ‘book’.

So i m writing a query in RoR model as

      Book.find(:all, :select => "book.name",
             :joins => "INNER JOIN money ON money.price =

book.price"+
“INNER JOIN card ON card.type = money.type”,
:conditions => “card.id = ‘10’”)

But this doesnt work.Is there any alternate query or i m missing
something in this query.

Any help would be appreciated.

Thanks in advance

Anandh

Well, I don’t know the answer, but you can probably use the sql query
mentioned in this page:
http://www.keithjbrown.co.uk/vworks/mysql/mysql_p5.php ( Do a browser
search
on string “Joining Three Tables”)

BTW, this email is to mention a different problem in your query: should
not
card be cards and book be books in your query (table names are, by
convention, plural in rails) Try that too, might work.

Thanks,
Abhinav


अभिनव
http://twitter.com/abhinav

On Tue, Sep 8, 2009 at 10:55 AM, Anandh K. <

2009/9/8 Anandh K. [email protected]:

book.price"+
        “INNER JOIN card ON card.type = money.type”,
        :conditions => “card.id = ‘10’”)

But this doesnt work.Is there any alternate query or i m missing
something in this query.

Don’t use a column called type, it is a reserved word in rails as it
is used in Single Table Inheritance. There are workarounds but much
better not to use it if possible.

You have not told us what are the relationships between the models.
If you set these up appropriately rails will almost always generate
the joins for you. If you have to specify joins explicitly then
possibly you have not set your relationships up correctly.

Colin

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