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module Arel
class Join < Relation
attr_reader :join_sql, :relation1, :relation2, :predicates
delegate :engine, :to => :relation1
hash_on :relation1
def initialize(join_sql, relation1, relation2 = Nil.new, *predicates)
@join_sql, @relation1, @relation2, @predicates = join_sql, relation1, relation2, predicates
end
def ==(other)
self.class == other.class and
predicates == other.predicates and (
(relation1 == other.relation1 and relation2 == other.relation2) or
(relation2 == other.relation1 and relation1 == other.relation2)
)
end
def attributes
(externalize(relation1).attributes +
externalize(relation2).attributes).collect { |a| a.bind(self) }
end
def joins(formatter = Sql::TableReference.new(self))
this_join = [
join_sql,
if relation2.aggregation?
relation2.to_sql(formatter)
else
relation2.table.table_sql(formatter)
end,
("ON" unless predicates.blank?),
predicates.collect { |p| p.bind(formatter.christener).to_sql }.join(' AND ')
].compact.join(" ")
[relation1.joins(formatter), this_join, relation2.joins(formatter)].compact.join(" ")
end
def selects
(externalize(relation1).selects + externalize(relation2).selects).collect { |s| s.bind(self) }
end
def name_for(relation)
@used_names ||= Hash.new(0)
@relation_names ||= Hash.new do |h, k|
@used_names[k.name] += 1
h[k] = k.name + (@used_names[k.name] > 1 ? "_#{@used_names[k.name]}" : '')
end
@relation_names[relation]
end
def table
relation1.aggregation?? relation1 : relation1.table
end
delegate :name, :to => :relation1
def relation_for(attribute)
x = [relation1[attribute], relation2[attribute]].select { |a| a =~ attribute }.min do |a1, a2|
(attribute % a1).size <=> (attribute % a2).size
end
if x.relation.aggregation?
x.relation
else
x.original_relation
end
end
private
def externalize(relation)
Externalizer.new(relation)
end
Externalizer = Struct.new(:relation) do
def selects
relation.aggregation?? [] : relation.selects
end
def attributes
relation.aggregation?? relation.attributes.collect(&:to_attribute) : relation.attributes
end
end
end
end
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