handle cyclic associations

lib/replicate/active_record.rb

@@ -252,18 +252,20 @@ def replicate_omit_attributes=(attribute_names)
       # id    - Primary key id of the record on the dump system. This must be
       #         translated to the local system and stored in the keymap.
       # attrs - Hash of attributes to set on the new record.
+      # local_id - to reload an object with given local id
       #
       # Returns the ActiveRecord object instance for the new record.
-      def load_replicant(type, id, attributes)
-        instance = replicate_find_existing_record(attributes) || new
+      def load_replicant(type, id, attributes, local_id = nil)
+        instance = replicate_find_existing_record(attributes, local_id) || new
         create_or_update_replicant instance, attributes
       end
 
       # Locate an existing record using the replicate_natural_key attribute
       # values.
       #
       # Returns the existing record if found, nil otherwise.
-      def replicate_find_existing_record(attributes)
+      def replicate_find_existing_record(attributes, id = nil)
+        return find_by_id(id) if not id.nil? and not find_by_id(id).nil?
         return if replicate_natural_key.empty?
         conditions = {}
         replicate_natural_key.each do |attribute_name|

lib/replicate/dumper.rb

@@ -22,6 +22,7 @@ class Dumper < Emitter
     # block  - Dump context block. If given, the end of the block's execution
     #          is assumed to be the end of the dump stream.
     def initialize(io=nil)
+      @seen = Hash.new { |hash,k| hash[k] = {} }
       @memo = Hash.new { |hash,k| hash[k] = {} }
       super() do
         marshal_to io if io
@@ -79,7 +80,8 @@ def dump(*objects)
       end
       objects = objects[0] if objects.size == 1 && objects[0].respond_to?(:to_ary)
       objects.each do |object|
-        next if object.nil? || dumped?(object)
+        next if object.nil? || dumped?(object) || seen?(object)
+        see!(object)
         if object.respond_to?(:dump_replicant)
           args = [self]
           args << opts unless object.method(:dump_replicant).arity == 1
@@ -90,16 +92,30 @@ def dump(*objects)
       end
     end
 
-    # Check if object has been written yet.
-    def dumped?(object)
+    # type and id helper
+    def type_and_id(object)
       if object.respond_to?(:replicant_id)
         type, id = object.replicant_id
       elsif object.is_a?(Array)
         type, id = object
       else
         return false
       end
-      @memo[type.to_s][id]
+      yield type, id
+    end
+
+    # Check if object has been written yet.
+    def dumped?(object)
+      type_and_id(object) { |type,id| @memo[type.to_s][id] }
+    end
+
+    # Check if object has been seen yet (needed for loop prevention)
+    def seen?(object)
+      type_and_id(object) { |type,id| @seen[type.to_s][id] }  
+    end
+
+    def see!(object)
+      type_and_id(object) { |type,id| @seen[type.to_s][id] = true }  
     end
 
     # Called exactly once per unique type and id. Emits to all listeners.
@@ -114,6 +130,7 @@ def write(type, id, attributes, object)
       type = type.to_s
       return if dumped?([type, id])
       @memo[type][id] = true
+      @seen[type].delete(id)
 
       emit type, id, attributes, object
     end

lib/replicate/loader.rb

@@ -16,6 +16,7 @@ class Loader < Emitter
 
     def initialize
       @keymap = Hash.new { |hash,k| hash[k] = {} }
+      @wait   = Hash.new { |hash,k| hash[k] = Hash.new { |hash2,k2| hash2[k2] = [] } }
       @stats  = Hash.new { |hash,k| hash[k] = 0 }
       super
     end
@@ -67,13 +68,18 @@ def read(io)
     # id    - Primary key id of the record on the dump system. This must be
     #         translated to the local system and stored in the keymap.
     # attrs - Hash of attributes to set on the new record.
+    # local_id - to reload an object with given local id
     #
     # Returns the new object instance.
-    def load(type, id, attributes)
+    def load(type, id, attributes, local_id = nil)
       model_class = constantize(type)
+      if not local_id.nil? and model_class.method(:load_replicant).arity != -4
+        warn "cannot reload #{type}(#{id}) since #{type}#load_replicant overriden and does not provide reload functionality"
+        return
+      end
       translate_ids type, id, attributes
       begin
-        new_id, instance = model_class.load_replicant(type, id, attributes)
+        new_id, instance = model_class.load_replicant(*([type, id, attributes, local_id].compact))
       rescue => boom
         warn "error: loading #{type} #{id} #{boom.class} #{boom}"
         raise
@@ -100,8 +106,9 @@ def translate_ids(type, id, attributes)
             if local_id = @keymap[referenced_type][remote_id]
               local_id
             else
+              @wait[referenced_type][remote_id] << [type, id, attributes.clone()]
               warn "warn: #{referenced_type}(#{remote_id}) not in keymap, " +
-                   "referenced by #{type}(#{id})##{key}"
+                   "referenced by #{type}(#{id})##{key}, added to wait list"
             end
           end
         if value.is_a?(Array)
@@ -121,6 +128,13 @@ def register_id(object, type, remote_id, local_id)
         @keymap[c.name][remote_id] = local_id
         c = c.superclass
       end
+      if not @wait[type][remote_id].nil?
+        @wait[type][remote_id].each do |waiting_object|
+          waiting_type, waiting_id, waiting_attributes = waiting_object
+          load(waiting_type, waiting_id, waiting_attributes, @keymap[waiting_type][waiting_id])
+        end
+        @wait[type].delete(remote_id)
+      end 
     end
 
     # Turn a string into an object by traversing constants. Identical to

test/active_record_test.rb

@@ -54,8 +54,20 @@
     t.integer "notable_id"
     t.string  "notable_type"
   end
-
+  
   create_table "namespaced", :force => true
+
+  create_table "orders", :force => true do |t|
+    t.string  "name"
+    t.integer "last_state_id"
+  end
+
+  create_table "states", :force => true do |t|
+    t.string    "name"
+    t.datetime  "created_at"
+    t.datetime  "updated_at"
+    t.integer   "order_id"
+  end
 end
 
 # models
@@ -94,6 +106,15 @@ class User::Namespaced < ActiveRecord::Base
   self.table_name = "namespaced"
 end
 
+class Order < ActiveRecord::Base
+  has_many    :states
+  belongs_to  :last_state, :class_name => 'State'
+end
+
+class State < ActiveRecord::Base
+  belongs_to  :order
+end 
+
 # The test case loads some fixture data once and uses transaction rollback to
 # reset fixture state for each test's setup.
 class ActiveRecordTest < Test::Unit::TestCase
@@ -193,6 +214,92 @@ def test_omit_dumping_of_association
     type, id, attrs, obj = objects.shift
     assert_equal 'User', type
   end
+
+  def test_dump_and_load_correctly_despite_association_cycle
+    objects = []
+    @dumper.listen { |type, id, attrs, obj| objects << [type, id, attrs, obj] }
+
+    Order.replicate_associations :states
+    o = Order.create! :name => 'beer'
+    s1 = State.create! :name => 'ordered', :order => o
+    s2 = State.create! :name => 'paid', :order => o
+    o.last_state = s2
+    o.save!
+
+    @dumper.dump o
+
+    assert_equal 3, objects.size
+
+    # last state is resolved by Order belongs_to and is dumped first
+    type, id, attrs, obj = objects[0]
+    assert_equal 'State', type
+    assert_equal 2, attrs['id']
+    assert_equal [:id, "Order", 1], attrs['order_id']
+
+    # next comes the order itself
+    type, id, attrs, obj = objects[1]
+    assert_equal 'Order', type
+    assert_equal 1, attrs['id']
+    assert_equal [:id, "State", 2], attrs['last_state_id']
+
+    # and finally the has_many states, in this case just one left
+    type, id, attrs, obj = objects[2]
+    assert_equal 'State', type
+    assert_equal 1, attrs['id']
+    assert_equal [:id, "Order", 1], attrs['order_id']
+
+    # destroy objects
+    State.delete_all
+    Order.delete_all
+
+    assert_equal 0, Order.all.count
+    assert_equal 0, State.all.count    
+
+    assert_equal 3, objects.size
+
+    # make more than one object to wait for referenced object
+    objects[1], objects[2] = objects[2], objects[1]
+
+    # restore dump
+    objects.each { |type, id, attrs, obj| @loader.feed type, id, attrs }
+
+    assert_equal 1, Order.all.count
+    assert_equal 2, State.all.count
+    # all states correctly linked to order?
+    assert_equal false, State.all.map {|s| s.order == Order.first}.include?(false)
+    # order linked to existing last_state?
+    assert_equal true, State.all.include?(Order.first.last_state)
+  end
+
+  def test_dump_and_load_with_overridden_load_replicant_method_if_association_cycle
+    objects = []
+    @dumper.listen { |type, id, attrs, obj| objects << [type, id, attrs, obj] }
+
+    (class << State; self end).class_eval do
+      define_method(:load_replicant) do |type, id, attrs|
+        super type, id, attrs
+      end
+    end
+
+    Order.replicate_associations :states
+    o = Order.create! :name => 'beer'
+    s1 = State.create! :name => 'ordered', :order => o
+    s2 = State.create! :name => 'paid', :order => o
+    o.last_state = s2
+    o.save!
+
+    @dumper.dump o
+
+    # destroy objects
+    State.delete_all
+    Order.delete_all
+
+    # restore dump
+    objects.each { |type, id, attrs, obj| @loader.feed type, id, attrs }
+
+    assert_equal 1, Order.all.count
+    assert_equal 2, State.all.count
+  end
 
   if ActiveRecord::VERSION::STRING[0, 3] > '2.2'
     def test_dump_and_load_non_standard_foreign_key_association