schema/field: support default values for json and other

schema/field/field.go

@@ -732,6 +732,28 @@ func (b *jsonBuilder) Annotations(annotations ...schema.Annotation) *jsonBuilder
 	return b
 }
 
+// Default sets the default value of the field. For example:
+//
+//	field.JSON("dirs", []http.Dir{}).
+//		// A static default value.
+//		Default([]http.Dir{"/tmp"})
+//
+//	field.JSON("dirs", []http.Dir{}).
+//		// A function for generating the default value.
+//		Default(DefaultDirs)
+//
+func (b *jsonBuilder) Default(v interface{}) *jsonBuilder {
+	b.desc.Default = v
+	switch fieldT, defaultT := b.desc.Info.RType.rtype, reflect.TypeOf(v); {
+	case fieldT == defaultT:
+	case defaultT.Kind() == reflect.Func:
+		b.desc.checkDefaultFunc(b.desc.Info.RType.rtype)
+	default:
+		b.desc.Err = fmt.Errorf("expect type (func() %[1]s) or (%[1]s) for other default value", b.desc.Info)
+	}
+	return b
+}
+
 // Descriptor implements the ent.Field interface by returning its descriptor.
 func (b *jsonBuilder) Descriptor() *Descriptor {
 	return b.desc

schema/field/field_test.go

@@ -467,13 +467,31 @@ func TestJSON(t *testing.T) {
 
 	fd = field.Strings("strings").
 		Optional().
+		Default([]string{"a", "b"}).
 		Descriptor()
+	assert.NoError(t, fd.Err)
 	assert.True(t, fd.Optional)
 	assert.Empty(t, fd.Info.PkgPath)
 	assert.Equal(t, "strings", fd.Name)
+	assert.Equal(t, []string{"a", "b"}, fd.Default)
 	assert.Equal(t, field.TypeJSON, fd.Info.Type)
 	assert.Equal(t, "[]string", fd.Info.String())
 
+	fd = field.JSON("dirs", []http.Dir{}).
+		Default([]http.Dir{"a", "b"}).
+		Descriptor()
+	assert.NoError(t, fd.Err)
+	fd = field.JSON("dirs", []http.Dir{}).
+		Default(func() []http.Dir {
+			return []http.Dir{"/tmp"}
+		}).
+		Descriptor()
+	assert.NoError(t, fd.Err)
+	fd = field.JSON("dirs", []http.Dir{}).
+		Default([]string{"a", "b"}).
+		Descriptor()
+	assert.Error(t, fd.Err)
+
 	fd = field.JSON("values", &url.Values{}).Descriptor()
 	assert.Equal(t, "net/url", fd.Info.PkgPath)
 	fd = field.JSON("values", []url.Values{}).Descriptor()