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module ActiveRecord
module Associations
class JoinDependency # :nodoc:
# A JoinPart represents a part of a JoinDependency. It is an abstract class, inherited
# by JoinBase and JoinAssociation. A JoinBase represents the Active Record which
# everything else is being joined onto. A JoinAssociation represents an association which
# is joining to the base. A JoinAssociation may result in more than one actual join
# operations (for example a has_and_belongs_to_many JoinAssociation would result in
# two; one for the join table and one for the target table).
class JoinPart # :nodoc:
# The Active Record class which this join part is associated 'about'; for a JoinBase
# this is the actual base model, for a JoinAssociation this is the target model of the
# association.
attr_reader :active_record
delegate :table_name, :column_names, :primary_key, :reflections, :arel_engine, :to => :active_record
def initialize(active_record)
@active_record = active_record
@cached_record = {}
@column_names_with_alias = nil
end
def aliased_table
Arel::Nodes::TableAlias.new table, aliased_table_name
end
def ==(other)
raise NotImplementedError
end
# An Arel::Table for the active_record
def table
raise NotImplementedError
end
# The prefix to be used when aliasing columns in the active_record's table
def aliased_prefix
raise NotImplementedError
end
# The alias for the active_record's table
def aliased_table_name
raise NotImplementedError
end
# The alias for the primary key of the active_record's table
def aliased_primary_key
"#{aliased_prefix}_r0"
end
# An array of [column_name, alias] pairs for the table
def column_names_with_alias
unless @column_names_with_alias
@column_names_with_alias = []
([primary_key] + (column_names - [primary_key])).compact.each_with_index do |column_name, i|
@column_names_with_alias << [column_name, "#{aliased_prefix}_r#{i}"]
end
end
@column_names_with_alias
end
def extract_record(row)
Hash[column_names_with_alias.map{|cn, an| [cn, row[an]]}]
end
def record_id(row)
row[aliased_primary_key]
end
def instantiate(row)
@cached_record[record_id(row)] ||= active_record.send(:instantiate, extract_record(row))
end
end
end
end
end
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