Fix #118 against 4-0-stable

[jsanders]

Fix for #118 against 4-0-stable.

This is really mostly @ofavre's work from awhile ago, I just updated it for 4-0-stable.

[ofavre]

Once merged, don't forget to update the code at yakaz/rails@29b8ebd (relation-unions-v3.2.2 branch), in order to resolve rails/rails#939!
EXCEPT and INTERSECT can be exposed too.
Thanks for taking this forward!

[bithive]

Thanks for your work on this @ofavre and @jsanders. I would love to see this get merged, as it is very helpful in one of my projects.

This may be unrelated but in using this new functionality I've noticed parameters don't seem to get bound when using associations in the method chain. I am working around this by writing e.g. Item.where(catalog: self) where I would normally just write items otherwise I get ActiveRecord::StatementInvalid: PG::UndefinedParameter: ERROR: there is no parameter $1

[jsanders]

@bithive: Hmm, haven't seen that... How do you have your association set up?

[bithive]

Hopefully this will make sense. It's not a big deal, and perhaps just a gap in my understanding of how to use Arel properly. I know what I am doing is unusual, but there is a reason.

create_table :values do |t|
  t.string :type,  null: false
  t.text   :value, null: true

  t.references :field, null: false
  t.references :item
  t.timestamps
end

class Value < ActiveRecord::Base
  belongs_to :field
  belongs_to :item
end

class Item < ActiveRecord::Base
  belongs_to :catalog
  has_many :values
end

class Catalog < ActiveRecord::Base
  has_many :items
  has_many :values, through: :items

  # This works for me
  def where attributes
    values_table = Value.arel_table

    queries = attributes.map do |key, value|
      Item.where(catalog: self).joins(:values).where(
        values_table[:field_id].eq(field_ids_from_tokens[key.to_s])
        .and(values_table[:value].eq(value))
      )
    end

    Item.find_by_sql queries.inject(&:intersect).to_sql
  end

  # This doesn't work
  def terse_where attributes
    queries = attributes.map do |key, value|
      values.where(field_id: field_ids_from_tokens[key.to_s], value: value)
    end

    Item.find_by_sql queries.inject(&:intersect).to_sql
  end
end

In the console first method generates SQL containing "items"."catalog_id" = 1 and succeeds while the latter generates "items"."catalog_id" = $1 and then complains about the undefined parameter.

[tamird]

did this ever actually get fixed on master?

[jsanders]

@tamird: No. I'm working on updating this patch for 5.0.1 (so that it can be used with rails 4.1) as we speak.

[tamird]

@jsanders I suggest writing the patch against master first

[jsanders]

@tamird: Took your advice :)

Closing this in favor of #320.