#12 allow dst not to have all src fields

Author: jeevatkm

model.go

@@ -680,7 +680,9 @@ func doCopy(dv, sv reflect.Value) []error {
 		// validate field - exists in dst, kind and type
 		err := validateCopyField(f, sfv, dfv)
 		if err != nil {
-			errs = append(errs, err)
+			if err != errFieldNotExists {
+				errs = append(errs, err)
+			}
 
 			continue
 		}

model_test.go

@@ -737,24 +737,6 @@ func TestCopyStructTypeDiffOnLevel1Interface(t *testing.T) {
 	assertEqual(t, src.Level1.Name, dst.Level1.(SampleLevelSrc).Name)
 }
 
-func TestCopyStructElementIsNotValidInDst(t *testing.T) {
-	type Source struct {
-		Name string
-		Year int
-	}
-
-	type Destination struct {
-		Name string
-	}
-
-	src := Source{Year: 2016}
-	dst := Destination{Name: "Value is gonna disappear"}
-
-	errs := Copy(&dst, src)
-
-	assertEqual(t, "Field: 'Year', does not exists in dst", errs[0].Error())
-}
-
 func TestCopyStructZeroValToDst(t *testing.T) {
 	type Source struct {
 		Name string
@@ -1896,29 +1878,6 @@ func TestKind(t *testing.T) {
 	assertEqual(t, true, reflect.Invalid == kind6)
 }
 
-func TestMissingDestField(t *testing.T) {
-
-	type C struct {
-	}
-
-	type A struct {
-		X string
-		Y string
-		Z C
-	}
-
-	type B struct {
-		X string
-	}
-
-	a := A{X: "X", Y: "Y", Z: C{}}
-	b := B{}
-	errs := Copy(&b, &a)
-	assertEqual(t, 2, len(errs))
-	assertEqual(t, "Field: 'Y', does not exists in dst", errs[0].Error())
-	assertEqual(t, "Field: 'Z', does not exists in dst", errs[1].Error())
-}
-
 func TestNestedStructToStructMapping(t *testing.T) {
 	type C struct {
 		X string
@@ -2155,6 +2114,30 @@ func TestSetField(t *testing.T) {
 	assertEqual(t, "Field: String, type/kind did not match", err.Error())
 }
 
+func TestImprovedCopy(t *testing.T) {
+	type DomainObject struct {
+		Name    string
+		Address string
+		Phone   string
+	}
+
+	type LoginGreeterDTO struct {
+		Name string
+	}
+
+	src := DomainObject{
+		Name:    "go-model",
+		Address: "123 sample street",
+		Phone:   "000-000-0000",
+	}
+
+	dst := LoginGreeterDTO{}
+
+	errs := Copy(&dst, src)
+	assertEqual(t, 0, len(errs))
+	assertEqual(t, "go-model", dst.Name)
+}
+
 //
 // helper test methods
 //

util.go

@@ -10,6 +10,8 @@ import (
 	"reflect"
 )
 
+var errFieldNotExists = errors.New("Field does not exists")
+
 func isFieldZero(f reflect.Value) bool {
 	// zero value of the given field
 	// For example: reflect.Zero(reflect.TypeOf(42)) returns a Value with Kind Int and value 0
@@ -35,7 +37,8 @@ func isNoTraverseType(v reflect.Value) bool {
 func validateCopyField(f reflect.StructField, sfv, dfv reflect.Value) error {
 	// check dst field is exists, if not valid move on
 	if !dfv.IsValid() {
-		return fmt.Errorf("Field: '%v', does not exists in dst", f.Name)
+		return errFieldNotExists
+		//return fmt.Errorf("Field does not exists in dst", f.Name)
 	}
 
 	if conversionExists(sfv.Type(), dfv.Type()) {