gistfile1.rb

assert_equal 1, posts(:welcome).tags.count


# Arel 1
# ------

SELECT TOP (1) [posts].* FROM [posts] WHERE ([posts].[id] = 1)

SELECT COUNT(DISTINCT [tags].[id]) AS count_id 
FROM [tags] 
LEFT OUTER JOIN [taggings] ON [taggings].[tag_id] = [tags].[id] 
INNER JOIN [taggings] AS [taggings_crltd] ON [tags].id = [taggings_crltd].tag_id 
WHERE (([taggings].taggable_id = 1) AND ([taggings].taggable_type = N'Post'))


# Arel 2
# ------

# core.source
# <Arel::Nodes::JoinSource:0x1023a0c20 
#   @left=#<Arel::Table:0x1023c1b50 
#     @aliases=[], @columns=nil, @engine=ActiveRecord::Base, 
#     @primary_key=nil, @table_alias=nil, @name="tags"
#   >, 
#   @right=[
#     #<Arel::Nodes::OuterJoin:0x1023a0cc0 
#       @left=#<Arel::Table:0x1023a16e8 
#         @aliases=[], @columns=nil, @engine=ActiveRecord::Base, 
#         @primary_key=nil, @table_alias=nil, @name="taggings"
#       >, 
#       @right=#<Arel::Nodes::On:0x1023a0d10 
#         @expr=#<Arel::Nodes::Equality:0x1023a0ea0 
#           @left=#<struct Arel::Attributes::Attribute 
#             relation=#<Arel::Table:0x1023a14e0 
#               @aliases=[], @columns=nil, @engine=ActiveRecord::Base, 
#               @primary_key=nil, @table_alias=nil, @name="taggings"
#             >, 
#             name="tag_id"
#           >, 
#           @right=#<struct Arel::Attributes::Attribute 
#             relation=#<Arel::Table:0x1023a1328 
#               @aliases=[], @columns=nil, @engine=ActiveRecord::Base, 
#               @primary_key=nil, @table_alias=nil, @name="tags"
#             >, 
#             name="id"
#           >
#         >
#       >
#     >, <-- Arel::Nodes::OuterJoin
#     #<Arel::Nodes::StringJoin:0x1023a0d88 
#       @left="INNER JOIN [taggings] ON [tags].id = [taggings].tag_id", 
#       @right=nil
#     >
#   ]
# >

# Find rails through relationship joins that need to be correlated. Would be something like.

  Arel::Nodes::JoinSource === core.source
  Arel::Nodes::OuterJoin  === core.source.right.first
  Arel::Nodes::StringJoin === core.source.right.second

  Arel::Nodes::OuterJoin  - LEFT OUTER JOIN [taggings] ON [taggings].[tag_id] = [tags].[id]
  Arel::Nodes::StringJoin - LEFT OUTER JOIN [taggings] AS [taggings_2] ON [taggings_2].[tag_id] = [tags].[id]

core.source.right.many?

j1 = core.source.right.first
j2 = core.source.right.second

j1tn = j1.left.name # => "taggings"
j2tn = j2.left.match(/JOIN \[(.*)\].*ON/).try(:[],1) # => "taggings"

visit core.source.right.first   # => "LEFT OUTER JOIN [taggings] ON [taggings].[tag_id] = [tags].[id]"
visit core.source.right.second  # => "INNER JOIN [taggings] ON [tags].id = [taggings].tag_id"

j1.left.table_alias = 'taggings_2'
visit(j1) # => "LEFT OUTER JOIN [taggings] [taggings_2] ON [taggings].[tag_id] = [tags].[id]"

j1.right.expr.left.relation.table_alias = 'taggings_2'
visit(j1) # => "LEFT OUTER JOIN [taggings] [taggings_2] ON [taggings_2].[tag_id] = [tags].[id]"