entc/gen: move eager-loading to method (#2790)

This is a preparation work for 'WithNamed<E>' API

examples/m2mbidi/ent/user_query.go

@@ -380,61 +380,70 @@ func (uq *UserQuery) sqlAll(ctx context.Context, hooks ...queryHook) ([]*User, e
 	if len(nodes) == 0 {
 		return nodes, nil
 	}
-
 	if query := uq.withFriends; query != nil {
-		edgeids := make([]driver.Value, len(nodes))
-		byid := make(map[int]*User)
-		nids := make(map[int]map[*User]struct{})
-		for i, node := range nodes {
-			edgeids[i] = node.ID
-			byid[node.ID] = node
-			node.Edges.Friends = []*User{}
-		}
-		query.Where(func(s *sql.Selector) {
-			joinT := sql.Table(user.FriendsTable)
-			s.Join(joinT).On(s.C(user.FieldID), joinT.C(user.FriendsPrimaryKey[1]))
-			s.Where(sql.InValues(joinT.C(user.FriendsPrimaryKey[0]), edgeids...))
-			columns := s.SelectedColumns()
-			s.Select(joinT.C(user.FriendsPrimaryKey[0]))
-			s.AppendSelect(columns...)
-			s.SetDistinct(false)
-		})
-		neighbors, err := query.sqlAll(ctx, func(_ context.Context, spec *sqlgraph.QuerySpec) {
-			assign := spec.Assign
-			values := spec.ScanValues
-			spec.ScanValues = func(columns []string) ([]interface{}, error) {
-				values, err := values(columns[1:])
-				if err != nil {
-					return nil, err
-				}
-				return append([]interface{}{new(sql.NullInt64)}, values...), nil
-			}
-			spec.Assign = func(columns []string, values []interface{}) error {
-				outValue := int(values[0].(*sql.NullInt64).Int64)
-				inValue := int(values[1].(*sql.NullInt64).Int64)
-				if nids[inValue] == nil {
-					nids[inValue] = map[*User]struct{}{byid[outValue]: struct{}{}}
-					return assign(columns[1:], values[1:])
-				}
-				nids[inValue][byid[outValue]] = struct{}{}
-				return nil
-			}
-		})
-		if err != nil {
+		if err := uq.loadFriends(ctx, query, nodes,
+			func(n *User) { n.Edges.Friends = []*User{} },
+			func(n *User, e *User) { n.Edges.Friends = append(n.Edges.Friends, e) }); err != nil {
 			return nil, err
 		}
-		for _, n := range neighbors {
-			nodes, ok := nids[n.ID]
-			if !ok {
-				return nil, fmt.Errorf(`unexpected "friends" node returned %v`, n.ID)
-			}
-			for kn := range nodes {
-				kn.Edges.Friends = append(kn.Edges.Friends, n)
-			}
+	}
+	return nodes, nil
+}
+
+func (uq *UserQuery) loadFriends(ctx context.Context, query *UserQuery, nodes []*User, init func(*User), assign func(*User, *User)) error {
+	edgeIDs := make([]driver.Value, len(nodes))
+	byID := make(map[int]*User)
+	nids := make(map[int]map[*User]struct{})
+	for i, node := range nodes {
+		edgeIDs[i] = node.ID
+		byID[node.ID] = node
+		if init != nil {
+			init(node)
 		}
 	}
-
-	return nodes, nil
+	query.Where(func(s *sql.Selector) {
+		joinT := sql.Table(user.FriendsTable)
+		s.Join(joinT).On(s.C(user.FieldID), joinT.C(user.FriendsPrimaryKey[1]))
+		s.Where(sql.InValues(joinT.C(user.FriendsPrimaryKey[0]), edgeIDs...))
+		columns := s.SelectedColumns()
+		s.Select(joinT.C(user.FriendsPrimaryKey[0]))
+		s.AppendSelect(columns...)
+		s.SetDistinct(false)
+	})
+	neighbors, err := query.sqlAll(ctx, func(_ context.Context, spec *sqlgraph.QuerySpec) {
+		assign := spec.Assign
+		values := spec.ScanValues
+		spec.ScanValues = func(columns []string) ([]interface{}, error) {
+			values, err := values(columns[1:])
+			if err != nil {
+				return nil, err
+			}
+			return append([]interface{}{new(sql.NullInt64)}, values...), nil
+		}
+		spec.Assign = func(columns []string, values []interface{}) error {
+			outValue := int(values[0].(*sql.NullInt64).Int64)
+			inValue := int(values[1].(*sql.NullInt64).Int64)
+			if nids[inValue] == nil {
+				nids[inValue] = map[*User]struct{}{byID[outValue]: struct{}{}}
+				return assign(columns[1:], values[1:])
+			}
+			nids[inValue][byID[outValue]] = struct{}{}
+			return nil
+		}
+	})
+	if err != nil {
+		return err
+	}
+	for _, n := range neighbors {
+		nodes, ok := nids[n.ID]
+		if !ok {
+			return fmt.Errorf(`unexpected "friends" node returned %v`, n.ID)
+		}
+		for kn := range nodes {
+			assign(kn, n)
+		}
+	}
+	return nil
 }
 
 func (uq *UserQuery) sqlCount(ctx context.Context) (int, error) {