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module Arel
class Expression < Attribute
attr_reader :attribute
alias :name :alias
def initialize(attribute, aliaz = nil, ancestor = nil)
super(attribute.relation, aliaz, :alias => aliaz, :ancestor => ancestor)
@attribute = attribute
end
def == other
super && Expression === other && attribute == other.attribute
end
def aggregation?
true
end
def to_sql(formatter = Sql::SelectClause.new(relation))
formatter.expression self
end
module Transformations
def as(aliaz)
self.class.new(attribute, aliaz, self)
end
def bind(new_relation)
new_relation == relation ? self : self.class.new(attribute.bind(new_relation), @alias, self)
end
def to_attribute(relation)
Attribute.new(relation, @alias, :ancestor => self)
end
end
include Transformations
end
class Count < Expression
def function_sql; 'COUNT' end
end
class Distinct < Expression
def function_sql; 'DISTINCT' end
end
class Sum < Expression
def function_sql; 'SUM' end
end
class Maximum < Expression
def function_sql; 'MAX' end
end
class Minimum < Expression
def function_sql; 'MIN' end
end
class Average < Expression
def function_sql; 'AVG' end
end
end
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