Class: Alf::Engine::Materialize::Hash

Inherits:
Object
  • Object
show all
Includes:
Cog, Alf::Engine::Materialize
Defined in:
lib/alf/engine/materialize/hash.rb

Overview

Provides in-memory materialization through a ruby Hash.

This class acts as a Cog, that it, it is an enumerable of tuples. No particular ordering is guaranteed. In addition, the class provides indexed access through the [] method.

Materialization occurs at prepare time, with auto-prepare on first access.

Example:

rel = [
  {:name => "Jones", :city => "London"},
  {:name => "Smith", :city => "Paris"},
  {:name => "Blake", :city => "London"}
]
op = Materialize::Hash.new(rel, AttrList[:city])

op.to_a 
# => same as rel, no ordering guaranteed

op[:city => "London"].to_a
# => [
       {:name => "Jones", :city => "London"},
       {:name => "Blake", :city => "London"}
     ]

op[:city => "London"].to_a
# => [
       {:name => "Jones", :city => "London"},
       {:name => "Blake", :city => "London"}
     ]

op[:city => "Athens"].to_a
# => []

Constant Summary

Constants included from Cog

Cog::EMPTY_CHILDREN, Cog::EMPTY_OPTIONS

Instance Attribute Summary collapse

Attributes included from Compiler::Cog

#compiler, #expr

Instance Method Summary collapse

Methods included from Cog

#arguments, #children, #each, #options, #to_s

Methods included from Compiler::Cog

#cog_orders, #orderedby?, #relation_type, #to_ascii_tree, #to_cog, #to_relation

Constructor Details

#initialize(operand, key, allbut = false, expr = nil, compiler = nil) ⇒ Hash

Creates a Materialize::Hash instance



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# File 'lib/alf/engine/materialize/hash.rb', line 54

def initialize(operand, key, allbut = false, expr = nil, compiler = nil)
  super(expr, compiler)
  @operand = operand
  @key = key
  @allbut = allbut
  @materialized = nil
end

Instance Attribute Details

#allbut ⇒ Boolean (readonly)

Returns Hash on all but specified attributes?.

Returns:

  • (Boolean) —

    Hash on all but specified attributes?



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# File 'lib/alf/engine/materialize/hash.rb', line 51

def allbut
  @allbut
end

#key ⇒ AttrList (readonly)

Returns Attributes for the hash key.

Returns:

  • (AttrList) —

    Attributes for the hash key



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# File 'lib/alf/engine/materialize/hash.rb', line 48

def key
  @key
end

#operand ⇒ Enumerable (readonly)

Returns The operand.

Returns:

  • (Enumerable) —

    The operand



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# File 'lib/alf/engine/materialize/hash.rb', line 45

def operand
  @operand
end

Instance Method Details

#[](key_tuple, project = false) ⇒ Cog

Returns tuples that match a given key.

This method returns a Cog instance in all case. En empty Cog is returned if no tuples match the key.

Parameters:

  • key_tuple (Tuple) —

    a key tuple

  • project (Boolean) (defaults to: false) —

    project key_tuple on key first?

Returns:

  • (Cog) —

    the tuples from operand that match key_tuple



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# File 'lib/alf/engine/materialize/hash.rb', line 82

def [](key_tuple, project = false)
  key_tuple = key_for(key_tuple) if project
  m = materialized
  m.has_key?(key_tuple) ? m[key_tuple] : []
end

#_each(&block) ⇒ Object 



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# File 'lib/alf/engine/materialize/hash.rb', line 63

def _each(&block)
  materialized.each_value do |rel|
    rel.each(&block)
  end
end

#clean ⇒ Object

Frees the materizalied hash



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# File 'lib/alf/engine/materialize/hash.rb', line 105

def clean
  @materialized = nil
end

#each_pair(&block) ⇒ Object

Yields indexed (key, tuples) pairs in turn.



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# File 'lib/alf/engine/materialize/hash.rb', line 70

def each_pair(&block)
  materialized.each_pair(&block)
end

#prepare ⇒ Object

Prepare through materialization of the operand as a hash



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# File 'lib/alf/engine/materialize/hash.rb', line 91

def prepare
  @materialized ||= begin
    h = ::Hash.new{|h,k| h[k] = []}
    operand.each do |tuple|
      h[key_for(tuple)] << tuple
    end
    h
  end
  self
end