Adding option tomatch array elements when comparing

README.md

@@ -37,6 +37,16 @@ If you want to exclude some keys from comparison use exclusion param:
     exclusion = ["from_user", "to_user_id"]
     result = JsonCompare.get_diff(old, new, exclusion)
 
+Alternative way for excluding keys from comparison:
+
+    exclusions = ["from_user", "to_user_id"]
+    result = JsonCompare.get_diff(old, new, excluded_key: excluded_keys)
+
+If you want to match array elements by a certain key:
+
+    result = JsonCompare.get_diff(old, new, matching_key: "id")
+
+
 ## Contributing
 
 1. Fork it

lib/json-compare.rb

@@ -2,9 +2,13 @@
 require 'json-compare/comparer'
 
 module JsonCompare
-  def self.get_diff(old, new, exclusion = [])
+  def self.get_diff(old, new, options = {})
+    if options.kind_of?(Array)
+      options = {:excluded_keys => options}
+    end
     comparer = JsonCompare::Comparer.new
-    comparer.excluded_keys = exclusion
+    comparer.excluded_keys = options.delete(:excluded_keys) || []
+    comparer.matching_key = options.delete(:matching_key)
     comparer.compare_elements(old,new)
   end
 end

lib/json-compare/comparer.rb

@@ -1,7 +1,7 @@
 module JsonCompare
   class Comparer
 
-    attr_accessor :excluded_keys
+    attr_accessor :excluded_keys, :matching_key
 
     def is_boolean(obj)
       !!obj == obj
@@ -51,26 +51,34 @@ def compare_hashes(old_hash, new_hash)
     end
 
     def compare_arrays(old_array, new_array)
-      old_array_length = old_array.count
+      has_comparing_way = !matching_key.nil?
+      result = get_diffs_struct
+      new_array_index = 0
       new_array_length = new_array.count
-      inters = [old_array.count, new_array.count].min
 
-      result = get_diffs_struct
+      old_array.each_with_index do |elem, index|
+        number = (new_array_index...new_array_length).detect do |n|
+          !(
+            has_comparing_way &&
+            elem.kind_of?(Hash) && elem.has_key?(matching_key) &&
+            new_array[n].kind_of?(Hash) && new_array[n].has_key?(matching_key)
+          ) || new_array[n][matching_key] == elem[matching_key]
+        end
 
-      (0..inters).map do |n|
-        res = compare_elements(old_array[n], new_array[n])
-        result[:update][n] = res unless (res.nil? || (res.respond_to?(:empty?) && res.empty?))
+        if number
+          res = compare_elements(elem, new_array[number])
+          result[:update][index] = res unless (res.nil? || (res.respond_to?(:empty?) && res.empty?))
+          (new_array_index...number).each do |n|
+            result[:append][n] = new_array[n]
+          end
+          new_array_index = number + 1
+        else
+          result[:remove][index] = elem
+        end
       end
 
-      # the rest of the larger array
-      if inters == old_array_length
-        (inters..new_array_length).each do |n|
-          result[:append][n] = new_array[n]
-        end
-      else
-        (inters..old_array_length).each do |n|
-          result[:remove][n] = old_array[n]
-        end
+      (new_array_index...new_array_length).each do |n|
+        result[:append][n] = new_array[n]
       end
 
       filter_results(result)
@@ -79,7 +87,7 @@ def compare_arrays(old_array, new_array)
     def compare_hash_array(old_hash, new_array)
       result = get_diffs_struct
 
-      (0..new_array.count).map do |n|
+      (0...new_array.count).map do |n|
         next if new_array[n].nil?
         if n == 0
           res = compare_elements(old_hash, new_array[0])

spec/lib/json-compare_spec.rb

@@ -129,7 +129,86 @@
 
     it "should compare arrays of fixnums" do
       result =  JsonCompare.get_diff([1, 2, 3], [1, 2, 3, 4])
-      result.should eq(:append => { 3 => 4 }, :update => { 3 => 4 })
+      result.should eq(:append => { 3 => 4 })
+    end
+  end
+
+
+  describe 'Arrays Comparison with matching condition' do
+    it "should treat as update" do
+      old = [{:id => '123'}]
+      new = [{:id => '456'}]
+      result = JsonCompare.get_diff(old, new, {})
+      result.should eq({
+        :update => {
+          0 => {:update => {:id => '456'}}
+        }
+      })
+    end
+
+    it "should treat as remove and append" do
+      old = [{:id => '123'}]
+      new = [{:id => '456'}]
+      result = JsonCompare.get_diff(old, new, {:matching_key => :id})
+      result.should eq({
+        :remove => {
+          0 => {:id => '123'}
+        },
+        :append => {
+          0 => {:id => '456'}
+        }
+      })
+    end
+
+    it "should treat as remove and append" do
+      old = [{:id => '123'}]
+      new = [{:id => '456'}, {:id => '123', :internal => true}, {:id => '789'}]
+      result = JsonCompare.get_diff(old, new, {:matching_key => :id})
+      result.should eq({
+        :update => {
+          0 => {
+            :append => {:internal => true}
+          }
+        },
+        :append => {
+          0 => {:id => '456'},
+          2 => {:id => '789'}
+        }
+      })
+    end
+
+    it "should follow the array's order when comparing" do
+      old = [{:id => '123'}, {:id => '456'}]
+      new = [{:id => '456'}, {:id => '123'}]
+      result = JsonCompare.get_diff(old, new, {:matching_key => :id})
+      result.should eq({
+        :append => {
+          0 => {:id => '456'}
+        },
+        :remove => {
+          1 => {:id => '456'}
+        }
+      })
+    end
+  end
+
+  describe 'Hash Array Comparison' do
+    it "should return empty hash" do
+      old_hash = {"ID" => "123"}
+      new_array = [{"ID" => "123"}]
+      result = JsonCompare.get_diff(old_hash, new_array)
+      result.should eq({})
+    end
+
+    it "should consider new array elements as append" do
+      old_hash = {"ID" => "123"}
+      new_array = [{"ID" => "123"}, {"ID" => "456"}]
+      result = JsonCompare.get_diff(old_hash, new_array)
+      result.should eq({
+        :append => {
+          1 => {"ID" => "456"}
+        }
+      })
     end
   end