I’m not satisfied with how rails currently handles finds accross
active record models, and want to see if there’s a waywe can improve
it.
The ability to generate dynamic search criteria from forms that search
accross models can be quite difficult except in the simplest cases.
The main cause of this is because as a developer you have to work out
what the table name is going to be called before you are able to use
it.
Here is an example:
class Person < ActiveRecord::Base
Everybody has a home address
belongs_to :home_address,
:class_name => ‘Address’,
:foreign_key => ‘home_address_id’
Only some people have a work address
belongs_to :work_address,
:class_name => ‘Address’,
:foreign_key => ‘work_address_id’
end
class Address < ActiveRecord::Base
end
Lets say we have a search panel, that allows you to filter on home
address street name, and work address street name and the user may or
may not use these search options.
A search for the home address 22
Person.find(:all, :joins =>
[:home_address, :work_address], :conditions => {:address =>
{:street_no => 22}})
A search for the work address 22
Person.find(:all, :joins =>
[:work_address, :home_address], :conditions => {:address =>
{:street_no => 22}})
#Notice that the order of the joins affects what the conditions hash
applies too. I believe this unintuitive.
I think a better system would be to use the names of the
relationships to dictate the search criteria
This would stop the user having to guess what the join table is
called.
Person.find(:all, :joins =>
[:work_address, :home_address], :conditions => {:home_address =>
{:street_no => 22}})
If this could be developed I would think we’d need to cover these
cases:
1. Eager loading using inner join
Person.find(:all, :joins =>
[:work_address, :home_address], :conditions => {:home_address =>
{:street_no => 22}})
2. Eager loading using left join
Notice that the home_address has conditions specified so in this
case we might want to enforce a left join
Person.find(:all, :include =>
[:work_address, :home_address], :conditions => {:home_address =>
{:street_no => 22}})
3.No eager loading specified (would we force a join because of the
conditions specified?)
Person.find(:all, :conditions => {:home_address => {:street_no =>
22}})
4. Custom SQL for each nesting, so that you can use any sql but not
have to explicitly know the name of the table
Person.find(
:all,
:joins => :home_address
:conditions => [
{:age => 22},
# This would currently conflict with the currect nested hash
since
{:home_address => [‘home_address.street_name LIKE ?’, ‘Dougla%’]}
]
)
1. Joins
SELECT *
FROM people
JOIN addresses home_address ON (people.home_address_id =
home_address.id)
WHERE people.age = 22 AND
home_address.street_name LIKE ‘Dougla%’
2. Left Joins (:include)
SELECT *
FROM people
WHERE people.age = 22
SELECT *
FROM addresses home_address
WHERE home_address.street_name LIKE ‘Dougla%’
AND home_address.id IN (1,2,3,4,5,6,7,8,9,10)
I’d like to hear your thoughts and ideas on any inherent problems with
getting this implemented, or design improvements.
It’s only an idea at this stage, but I’d like to develop it so that
developing complex dynamic searches using rails
becomes trivial.