schema/field: allow non-string ValueScanner types for enum fields (#1577)

* Make non-string ValueScanner types work with enum fields

This change fixes #1575 which now makes it possible to specify a GoType
for an enum that is not a string alias. It requires that if the specified
type is not a string alias, the type must satisfy the Stringer interface.

* remove default, rename field

* wip

* remove comment

* go generate

* make optional

* generate 🤦

* handle NULL case

* turns out mysql stores strings as []uint8

schema/field/field.go

@@ -808,6 +808,12 @@ type EnumValues interface {
 func (b *enumBuilder) GoType(ev EnumValues) *enumBuilder {
 	b.Values(ev.Values()...)
 	b.desc.goType(ev, stringType)
+	// If an error already exists, let that be returned instead.
+	// Otherwise check that the underlying type is either a string
+	// or implements Stringer.
+	if b.desc.Err == nil && b.desc.Info.RType.rtype.Kind() != reflect.String && !b.desc.Info.Stringer() {
+		b.desc.Err = errors.New("enum values which implement ValueScanner must also implement Stringer")
+	}
 	return b
 }
 

schema/field/field_test.go

@@ -7,6 +7,7 @@ package field_test
 import (
 	"database/sql"
 	"database/sql/driver"
+	"errors"
 	"net"
 	"net/http"
 	"net/url"
@@ -470,6 +471,45 @@ func (Role) Values() []string {
 	return []string{"admin", "owner"}
 }
 
+type RoleInt int32
+
+func (RoleInt) Values() []string {
+	return []string{"unknown", "admin", "owner"}
+}
+
+func (i RoleInt) String() string {
+	switch i {
+	case 1:
+		return "admin"
+	case 2:
+		return "owner"
+	default:
+		return "unknown"
+	}
+}
+
+func (i RoleInt) Value() (driver.Value, error) {
+	return i.String(), nil
+}
+
+func (i *RoleInt) Scan(val interface{}) error {
+	switch v := val.(type) {
+	case string:
+		switch v {
+		case "admin":
+			*i = 1
+		case "owner":
+			*i = 2
+		default:
+			*i = 0
+		}
+	default:
+		return errors.New("bad enum value")
+	}
+
+	return nil
+}
+
 func TestField_Enums(t *testing.T) {
 	fd := field.Enum("role").
 		Values(
@@ -505,6 +545,18 @@ func TestField_Enums(t *testing.T) {
 	assert.False(t, fd.Info.ValueScanner())
 	assert.Equal(t, "admin", fd.Enums[0].V)
 	assert.Equal(t, "owner", fd.Enums[1].V)
+	assert.False(t, fd.Info.Stringer())
+
+	fd = field.Enum("role").GoType(RoleInt(0)).Descriptor()
+	assert.Equal(t, "field_test.RoleInt", fd.Info.Ident)
+	assert.Equal(t, "entgo.io/ent/schema/field_test", fd.Info.PkgPath)
+	assert.Equal(t, "field_test.RoleInt", fd.Info.String())
+	assert.False(t, fd.Info.Nillable)
+	assert.True(t, fd.Info.ValueScanner())
+	assert.Equal(t, "unknown", fd.Enums[0].V)
+	assert.Equal(t, "admin", fd.Enums[1].V)
+	assert.Equal(t, "owner", fd.Enums[2].V)
+	assert.True(t, fd.Info.Stringer())
 }
 
 func TestField_UUID(t *testing.T) {