Allow insert giving default value (#540)

spec/operations/save_operation_spec.cr

@@ -421,6 +421,14 @@ describe "Avram::SaveOperation" do
         end
       end
 
+      it "allows supplying a value that matches the default" do
+        result = Company::SaveOperation.create!(sales: 0_i64, earnings: 0_i64)
+        default_result = Company::SaveOperation.create!
+
+        result.sales.should eq default_result.sales
+        result.earnings.should eq default_result.earnings
+      end
+
       it "overrides all of the defaults through params" do
         published_at = 1.day.ago.to_utc.at_beginning_of_day
         drafted_at = 1.week.ago.to_utc.at_beginning_of_day

spec/support/models/company.cr

@@ -1,6 +1,6 @@
 class Company < BaseModel
   table do
-    column sales : Int64
-    column earnings : Float64
+    column sales : Int64 = 0_i64
+    column earnings : Float64 = 0.0
   end
 end

src/avram/save_operation.cr

@@ -277,13 +277,7 @@ abstract class Avram::SaveOperation(T)
   end
 
   def changes : Hash(Symbol, String?)
-    _changes = {} of Symbol => String?
-    column_attributes.each do |attribute|
-      if attribute.changed?
-        _changes[attribute.name] = cast_value(attribute.value)
-      end
-    end
-    _changes
+    attributes_to_hash(column_attributes.select(&.changed?))
   end
 
   macro add_cast_value_methods(columns)
@@ -390,6 +384,11 @@ abstract class Avram::SaveOperation(T)
   end
 
   private def insert_sql
-    Avram::Insert.new(table_name, changes, T.column_names)
+    insert_values = attributes_to_hash(column_attributes).compact
+    Avram::Insert.new(table_name, insert_values, T.column_names)
+  end
+
+  private def attributes_to_hash(attributes) : Hash(Symbol, String?)
+    attributes.map { |attribute| {attribute.name, cast_value(attribute.value)} }.to_h
   end
 end