entc/gen/mutation: add IDs method for mutations

examples/version/ent/mutation.go

@@ -8,6 +8,7 @@ package ent
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"sync"
 
@@ -74,7 +75,7 @@ func withUserID(id int) userOption {
 		m.oldValue = func(ctx context.Context) (*User, error) {
 			once.Do(func() {
 				if m.done {
-					err = fmt.Errorf("querying old values post mutation is not allowed")
+					err = errors.New("querying old values post mutation is not allowed")
 				} else {
 					value, err = m.Client().User.Get(ctx, id)
 				}
@@ -107,7 +108,7 @@ func (m UserMutation) Client() *Client {
 // it returns an error otherwise.
 func (m UserMutation) Tx() (*Tx, error) {
 	if _, ok := m.driver.(*txDriver); !ok {
-		return nil, fmt.Errorf("ent: mutation is not running in a transaction")
+		return nil, errors.New("ent: mutation is not running in a transaction")
 	}
 	tx := &Tx{config: m.config}
 	tx.init()
@@ -123,6 +124,25 @@ func (m *UserMutation) ID() (id int, exists bool) {
 	return *m.id, true
 }
 
+// IDs queries the database and returns the entity ids that match the mutation's predicate.
+// That means, if the mutation is applied within a transaction with an isolation level such
+// as sql.LevelSerializable, the returned ids match the ids of the rows that will be updated
+// or updated by the mutation.
+func (m *UserMutation) IDs(ctx context.Context) ([]int, error) {
+	switch {
+	case m.op.Is(OpUpdateOne | OpDeleteOne):
+		id, exists := m.ID()
+		if exists {
+			return []int{id}, nil
+		}
+		fallthrough
+	case m.op.Is(OpUpdate | OpDelete):
+		return m.Client().User.Query().Where(m.predicates...).IDs(ctx)
+	default:
+		return nil, fmt.Errorf("IDs is not allowed on %s operations", m.op)
+	}
+}
+
 // SetVersion sets the "version" field.
 func (m *UserMutation) SetVersion(i int64) {
 	m.version = &i
@@ -143,10 +163,10 @@ func (m *UserMutation) Version() (r int64, exists bool) {
 // An error is returned if the mutation operation is not UpdateOne, or the database query fails.
 func (m *UserMutation) OldVersion(ctx context.Context) (v int64, err error) {
 	if !m.op.Is(OpUpdateOne) {
-		return v, fmt.Errorf("OldVersion is only allowed on UpdateOne operations")
+		return v, errors.New("OldVersion is only allowed on UpdateOne operations")
 	}
 	if m.id == nil || m.oldValue == nil {
-		return v, fmt.Errorf("OldVersion requires an ID field in the mutation")
+		return v, errors.New("OldVersion requires an ID field in the mutation")
 	}
 	oldValue, err := m.oldValue(ctx)
 	if err != nil {
@@ -198,10 +218,10 @@ func (m *UserMutation) Status() (r user.Status, exists bool) {
 // An error is returned if the mutation operation is not UpdateOne, or the database query fails.
 func (m *UserMutation) OldStatus(ctx context.Context) (v user.Status, err error) {
 	if !m.op.Is(OpUpdateOne) {
-		return v, fmt.Errorf("OldStatus is only allowed on UpdateOne operations")
+		return v, errors.New("OldStatus is only allowed on UpdateOne operations")
 	}
 	if m.id == nil || m.oldValue == nil {
-		return v, fmt.Errorf("OldStatus requires an ID field in the mutation")
+		return v, errors.New("OldStatus requires an ID field in the mutation")
 	}
 	oldValue, err := m.oldValue(ctx)
 	if err != nil {