Loading ActiveRecords via a complex query

Rails
1

Ok, I have a many_to_many relationship between two tables (A, B)
implemented by a join table (J). J has two columns: a_id and b_id.

Currently, I use a query like this:

recs = A.find :all, :select => ‘A.*’,
:joins => ‘, B, J’,
:conditions => 'A.id = J.a_id AND J.b_id =
B.id AND B.somefield = somevalue ’

That works well, but is there a more Rails like way to do it?

Also, is there a more efficient way to do it? Notice in my RoR code,
I’m joining 3 tables together in a single SQL statement. Would it be
faster to select ids in an SQL call joining only 2 tables, then calling
A.find :all, ids?

In code:

ids_array = “SELECT J.a_id FROM J, B WHERE J.b_id = B.id AND
B.somefield = somevalue”
recs = A.find :all, ids_array

How do I efficiently execute that query and get an array of ids in
return?

Thanks for the help.

2

You have two options.

has_and_belongs_to_many :foo

Each of the two models that’s gonna be joined has a
has_and_belongs_to_many :other_model in it. Say your models are called
Book and Author - the table would then be named authors_books (plural
and in alphabetic order). The authors_books table would have two
columns: book_id and author_id. No primary key.

has_many :foo, :through => :bar

A bit to intricate to explain. Look at this pastie:
http://pastie.caboo.se/34094

On Jan 18, 9:15 pm, “Christopher J. Bottaro” [email protected]

3

I know how join tables work pertaining to Rails models. I’m asking
about how to load records using complex queries that involve join
tables.

See my pastie:
http://pastie.caboo.se/34129

Thanks.