Add ids method AF query

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Not released
 
+- Add `ids` method to ActiveQuery interface (https://github.com/Beyond-Finance/active_force/pull/94)
+
 ## 0.21.1
 - Fixes #91. Applies scopes to eager-loaded associations when they are nested. (https://github.com/Beyond-Finance/active_force/pull/92)
 

lib/active_force/active_query.rb

@@ -83,6 +83,10 @@ def select *selected_fields
       super *selected_fields
     end
 
+    def ids
+      clone_and_set_instance_variables(query_fields: ["Id"])
+    end
+
     def find!(id)
       result = find(id)
       raise RecordNotFound.new("Couldn't find #{table_name} with id #{id}", table_name, id: id) if result.nil?

spec/active_force/active_query_spec.rb

@@ -117,6 +117,12 @@ def self.decorate(records)
     end
   end
 
+  describe '#ids' do
+    it 'returns a query that selects only the Id field' do
+      expect(active_query.where(field: 123).ids.to_s).to eq "SELECT Id FROM table_name WHERE (Field__c = 123)"
+    end
+  end
+
   describe "condition mapping" do
     it "maps conditions for a .where" do
       new_query = active_query.where(field: 123)