refactor: move complex conditional to a method

The `f.SQLDefault == ""` part seems redundant before addReturningField,
as RETURNING makes sense for a field that was given its default value.

internal/dbtest/query_test.go

@@ -331,8 +331,8 @@ func TestQuery(t *testing.T) {
 				Where("model.id = _data.id")
 		},
 		func(db *bun.DB) schema.QueryAppender {
-			// "nullzero" marshalls zero values as DEFAULT or NULL (if DEFAULT placeholder is not supported)
-			// DB drivers that support DEFAULT placeholder resolve it to NULL for columns that do not have a DEFAULT value.
+			// "nullzero" marshals zero values as DEFAULT or NULL (if DEFAULT placeholder is not supported)
+			// DB drivers which support DEFAULT placeholder resolve it to NULL for columns that do not have a DEFAULT value.
 			type Model struct {
 				Int  int64     `bun:",nullzero"`
 				Uint uint64    `bun:",nullzero"`
@@ -1026,7 +1026,7 @@ func TestQuery(t *testing.T) {
 			}).Column("is_active").WherePK()
 		},
 		func(db *bun.DB) schema.QueryAppender {
-			// "default" marshalls zero values as DEFAULT or specified default value
+			// "default" marshals zero values as DEFAULT or the specified default value
 			type Model struct {
 				Int      int64     `bun:",default:42"`
 				Uint     uint64    `bun:",default:42"`

query_insert.go

@@ -332,7 +332,7 @@ func (q *InsertQuery) appendStructValues(
 		switch {
 		case isTemplate:
 			b = append(b, '?')
-		case f.IsPtr && f.HasNilValue(strct), f.HasZeroValue(strct) && (f.NullZero || f.SQLDefault != ""):
+		case q.marshalsToDefault(f, strct):
 			if q.db.HasFeature(feature.DefaultPlaceholder) {
 				b = append(b, "DEFAULT"...)
 			} else if f.SQLDefault != "" {
@@ -410,18 +410,23 @@ func (q *InsertQuery) getFields() ([]*schema.Field, error) {
 			q.addReturningField(f)
 			continue
 		}
-		if f.NotNull && f.SQLDefault == "" {
-			if (f.IsPtr && f.HasNilValue(strct)) || (f.NullZero && f.HasZeroValue(strct)) {
-				q.addReturningField(f)
-				continue
-			}
+		if f.NotNull && q.marshalsToDefault(f, strct) {
+			q.addReturningField(f)
+			continue
 		}
 		fields = append(fields, f)
 	}
 
 	return fields, nil
 }
 
+// marshalsToDefault checks if the value will be marshaled as DEFAULT or NULL (if DEFAULT placeholder is not supported)
+// when appending it to the VALUES clause in place of the given field.
+func (q InsertQuery) marshalsToDefault(f *schema.Field, v reflect.Value) bool {
+	return (f.IsPtr && f.HasNilValue(v)) ||
+		(f.HasZeroValue(v) && (f.NullZero || f.SQLDefault != ""))
+}
+
 func (q *InsertQuery) appendFields(
 	fmter schema.Formatter, b []byte, fields []*schema.Field,
 ) []byte {