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Sequel::Plugins::IdentityMap::ClassMethods

Public Instance Methods

associate(type, name, opts = {}, &block) click to toggle source

Override the default :eager_loader option for many_*_many associations to work with an identity_map. If the :eager_graph association option is used, you'll probably have to use :uniq=>true on the current association and :cartesian_product_number=>2 on the association mentioned by :eager_graph, otherwise you'll end up with duplicates because the row proc will be getting called multiple times for the same object. If you do have duplicates and you use :eager_graph, they'll probably be lost. Making that work correctly would require changing a lot of the core architecture, such as how graphing and eager graphing work.

# File lib/sequel/plugins/identity_map.rb, line 48
def associate(type, name, opts = {}, &block)
  if opts[:eager_loader]
    super
  elsif type == :many_to_many
    opts = super
    el = opts[:eager_loader] 
    model = self
    left_pk = opts[:left_primary_key]
    uses_lcks = opts[:uses_left_composite_keys]
    uses_rcks = opts[:uses_right_composite_keys]
    right = opts[:right_key]
    rcks = opts[:right_keys]
    join_table = opts[:join_table]
    left = opts[:left_key]
    lcks = opts[:left_keys]
    left_key_alias = opts[:left_key_alias] ||= opts.default_associated_key_alias
    opts[:eager_loader] = lambda do |eo|
      return el.call(eo) unless model.identity_map
      h = eo[:id_map]
      eo[:rows].each{|object| object.associations[name] = []}
      r = uses_rcks ? rcks.zip(opts.right_primary_keys) : [[right, opts.right_primary_key]]
      l = uses_lcks ? [[lcks.map{|k| SQL::QualifiedIdentifier.new(join_table, k)}, h.keys]] : [[left, h.keys]]

      # Replace the row proc to remove the left key alias before calling the previous row proc.
      # Associate the value of the left key alias with the associated object (through its object_id).
      # When loading the associated objects, lookup the left key alias value and associate the
      # associated objects to the main objects if the left key alias value matches the left primary key
      # value of the main object.
      # 
      # The deleting of the left key alias from the hash before calling the previous row proc
      # is necessary when an identity map is used, otherwise if the same associated object is returned more than
      # once for the association, it won't know which of current objects to associate it to.
      ds = opts.associated_class.inner_join(join_table, r + l)
      pr = ds.row_proc
      h2 = {}
      ds.row_proc = proc do |hash|
        hash_key = if uses_lcks
          left_key_alias.map{|k| hash.delete(k)}
        else
          hash.delete(left_key_alias)
        end
        obj = pr.call(hash)
        (h2[obj.object_id] ||= []) << hash_key
        obj
      end
      model.eager_loading_dataset(opts, ds, Array(opts.select), eo[:associations], eo) .all do |assoc_record|
        if hash_keys = h2.delete(assoc_record.object_id)
          hash_keys.each do |hash_key|
            if objects = h[hash_key]
              objects.each{|object| object.associations[name].push(assoc_record)}
            end
          end
        end
      end
    end
    opts
  elsif type == :many_through_many
    opts = super
    el = opts[:eager_loader] 
    model = self
    left_pk = opts[:left_primary_key]
    left_key = opts[:left_key]
    uses_lcks = opts[:uses_left_composite_keys]
    left_keys = Array(left_key)
    left_key_alias = opts[:left_key_alias]
    opts[:eager_loader] = lambda do |eo|
      return el.call(eo) unless model.identity_map
      h = eo[:id_map]
      eo[:rows].each{|object| object.associations[name] = []}
      ds = opts.associated_class 
      opts.reverse_edges.each{|t| ds = ds.join(t[:table], Array(t[:left]).zip(Array(t[:right])), :table_alias=>t[:alias])}
      ft = opts.final_reverse_edge
      conds = uses_lcks ? [[left_keys.map{|k| SQL::QualifiedIdentifier.new(ft[:table], k)}, h.keys]] : [[left_key, h.keys]]

      # See above comment in many_to_many eager_loader
      ds = ds.join(ft[:table], Array(ft[:left]).zip(Array(ft[:right])) + conds, :table_alias=>ft[:alias])
      pr = ds.row_proc
      h2 = {}
      ds.row_proc = proc do |hash|
        hash_key = if uses_lcks
          left_key_alias.map{|k| hash.delete(k)}
        else
          hash.delete(left_key_alias)
        end
        obj = pr.call(hash)
        (h2[obj.object_id] ||= []) << hash_key
        obj
      end
      model.eager_loading_dataset(opts, ds, Array(opts.select), eo[:associations], eo).all do |assoc_record|
        if hash_keys = h2.delete(assoc_record.object_id)
          hash_keys.each do |hash_key|
            if objects = h[hash_key]
              objects.each{|object| object.associations[name].push(assoc_record)}
            end
          end
        end
      end
    end
    opts
  else
    super
  end
end
call(row) click to toggle source

If the identity map is in use, check it for a current copy of the object. If a copy does not exist, create a new object and add it to the identity map. If a copy exists, add any values in the given row that aren't currently in the object to the object's values. This allows you to only request certain fields in an initial query, make modifications to some of those fields and request other, potentially overlapping fields in a new query, and not have the second query override fields you modified.

# File lib/sequel/plugins/identity_map.rb, line 172
def call(row)
  return super unless (idm = identity_map) && (pk = primary_key)
  if (k = identity_map_key(Array(pk).map{|x| row[x]})) && (o = idm[k])
    o.merge_db_update(row)
  else
    o = super
    if (k = identity_map_key(o.pk))
      idm[k] = o
    end
  end
  o
end
identity_map() click to toggle source

Returns the current thread-local identity map. Should be a hash if there is an active identity map, and nil otherwise.

# File lib/sequel/plugins/identity_map.rb, line 154
def identity_map
  Thread.current[:sequel_identity_map]
end
identity_map_key(pk) click to toggle source

The identity map key for an object of the current class with the given pk. May not always be correct for a class which uses STI.

# File lib/sequel/plugins/identity_map.rb, line 160
def identity_map_key(pk)
  pk = Array(pk)
  "#{self}:#{pk.join(',')}" unless pk.compact.empty?
end
with_identity_map() click to toggle source

Take a block and inside that block use an identity map to ensure a 1-1 correspondence of objects to the database row they represent.

# File lib/sequel/plugins/identity_map.rb, line 187
def with_identity_map
  return yield if identity_map
  begin
    self.identity_map = {}
    yield
  ensure
    self.identity_map = nil
  end
end

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