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require 'amalgalite/sqlite3/database/function'
module Amalgalite
#
# A Base class to inherit from for creating your own SQL aggregate functions
# in ruby.
#
# These are SQL functions similar to _max(X)_, _count(X)_, _avg(X)_. The built
# in SQLite aggregate functions are:
#
# * http://www.sqlite.org/lang_aggfunc.html
#
# If you choose to use Aggregate as a parent class of your SQL scalar function
# implementation you must:
#
# * implement _initalize_ with 0 arguments
# * set the @arity data member
# * set the @name data member
# * implement _step_ with arity of +@arity+
# * implement _finalize_ with arity of 0
#
# For instance to implement a <i>unique_word_count(X)</i> aggregate function you could
# implement it as:
#
# class UniqueWordCount < ::Amalgalite::Aggregate
# attr_accessor :words
#
# def initialize
# @name = 'unique_word_count'
# @arity = 1
# @words = Hash.new { |h,k| h[k] = 0 }
# end
#
# def step( str )
# str.split(/\W+/).each do |word|
# words[ word.downcase ] += 1
# end
# return nil
# end
#
# def finalize
# return words.size
# end
# end
#
#
class Aggregate
# The name of the SQL function
attr_accessor :name
# The arity of the SQL function
attr_accessor :arity
# finalize should return the final value of the aggregate function
def finalize
raise NotImplementedError, "Aggregate#finalize must be implemented"
end
# <b>Do Not Override</b>
#
# The function signature for use by the Amaglaite datase in tracking
# function creation.
#
def signature
@signature ||= ::Amalgalite::SQLite3::Database::Function.signature( self.name, self.arity )
end
end
end
Version data entries
62 entries across 62 versions & 2 rubygems