> > Hm, but how does it know to return a set object from the product_filter > table rather than the product or filter table?
Set objects are not associated with a particular table -- they represent a set of records to be returned by the db, which may involve a join of multiple tables. Basically, the Set object specifies the WHERE clauses in a SQL query. > And what does these two queries mean when it comes executing the queries? > (db.products.id == db.product_filter.product_id) & > (db.filters.id == db.product_filter.filter_id) & > In SQL, there are two ways to specify an inner join -- one is by using the INNER JOIN (or just JOIN) command, and the other is by adding a WHERE clause that equates the primary key of one table with the associated foreign key from the other table. The above queries are using the latter method (in web2py, to use the former method, you pass the "join" argument to the .select() method). > Does it work something like this: > > Return the set object that contains the filter name "hoodie" > (db.filters.name == "hoodie") > > Then, knowing the id of the filter from the previous result set, find all > the matching filter id in the product_filter table. > (db.filters.id == db.product_filter.filter_id) > > Now find all the products that has the same filter ids? > (db.products.id == db.product_filter.product_id) & > No, the above find products with id's that match the product_id of the records from db.product_filter, not that match the filter id's (there are no filter id's in the db.products table). As noted above, the immediately preceding two queries are used to join the db.product_filter table to the db.filters and db.products tables, respectively. This is necessary because this is a many-to-many relationship. Anthony -- --- You received this message because you are subscribed to the Google Groups "web2py-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to web2py+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
