diff --git a/internal/mopertest/aggregation_test.go b/internal/mopertest/aggregation_test.go
index 342b39a..736c464 100644
--- a/internal/mopertest/aggregation_test.go
+++ b/internal/mopertest/aggregation_test.go
@@ -2,55 +2,75 @@ package mopertest
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"testing"
 
 	"github.com/func25/mongofunc/mocom"
 	"github.com/func25/mongofunc/moper"
-	"go.mongodb.org/mongo-driver/bson"
-	"go.mongodb.org/mongo-driver/bson/primitive"
-	"go.mongodb.org/mongo-driver/mongo"
 	"go.mongodb.org/mongo-driver/mongo/options"
 )
 
-func TestAggregationTest(t *testing.T) {
-	matchStage := bson.D{
-		{
-			Key:   "$match",
-			Value: moper.D{}.InEll("damage", 1, 2, 3, 4, 5, 6, 7, 8, 9),
-		},
+func TestAggregation(t *testing.T) {
+	intArr := []int{1, 2, 3, 4, 5, 6, 7, 8, 9}
+
+	matchStage := moper.D{}.MatchD(moper.D{}.InArray("damage", intArr))
+	groupStage := moper.D{}.Group(
+		moper.P{K: "_id", V: nil},
+		moper.P{K: "total", V: moper.D{}.Sum("damage")},
+	)
+
+	req := &mocom.AggregationRequest[Hero]{
+		Pipeline: []moper.D{matchStage, groupStage},
+		Options:  []*options.AggregateOptions{},
+	}
+	result, err := mocom.Aggregate(context.Background(), req)
+	if err != nil {
+		t.Error(err)
+		return
 	}
 
-	groupStage := bson.D{
-		{
-			Key: "$group",
-			Value: bson.D{
-				{
-					Key:   "_id",
-					Value: nil,
-				},
-				{
-					Key: "total",
-					Value: bson.D{
-						{
-							Key:   "$sum",
-							Value: "$damage",
-						},
-					},
-				},
-			},
-		},
+	expect := 0
+	for _, v := range intArr {
+		expect += v * v
 	}
 
+	if int(result[0]["total"].(int32)) != expect {
+		t.Error("wrong result", result[0]["total"], expect)
+	}
+}
+
+func TestLookup(t *testing.T) {
+	intArr := []int{1}
+	matchStage := moper.D{}.MatchD(moper.D{}.InArray("damage", intArr))
+
+	lookupStage := moper.D{}.LookUp().
+		From(Weapon{}.CollName()).
+		LocalField("damage").
+		ForeignField("damage").
+		As("weapon")
+
+	unwindStage := moper.D{}.Equal("$unwind", moper.D{}.Equal("path", "$weapon").Equal("preserveNullAndEmptyArrays", false))
+
 	req := &mocom.AggregationRequest[Hero]{
-		Pipeline: mongo.Pipeline{matchStage, groupStage},
+		Pipeline: []moper.D{matchStage, lookupStage.D(), unwindStage},
 		Options:  []*options.AggregateOptions{},
-		Result:   []primitive.M{},
 	}
-	if err := mocom.Aggregate(context.Background(), req); err != nil {
+	result, err := mocom.Aggregate(context.Background(), req)
+	if err != nil {
 		t.Error(err)
 		return
 	}
 
-	fmt.Println(req.Result)
+	x, err := json.Marshal(result)
+	fmt.Println(string(x))
+
+	// expect := 0
+	// for _, v := range intArr {
+	// 	expect += v * v
+	// }
+
+	// if result[0]["total"] != expect {
+	// 	t.Error("wrong result", result[0]["total"], expect)
+	// }
 }
diff --git a/internal/mopertest/element_test.go b/internal/mopertest/element_test.go
index a8a2a31..91ebf50 100644
--- a/internal/mopertest/element_test.go
+++ b/internal/mopertest/element_test.go
@@ -10,7 +10,6 @@ import (
 
 func TestExists(t *testing.T) {
 	ctx := context.Background()
-
 	filter := moper.D{}.Exists("omit", true)
 	if count, err := mocom.Count[Hero](ctx, filter); err != nil {
 		t.Error("[TestExists]", err)
diff --git a/internal/mopertest/seed.go b/internal/mopertest/seed.go
index 7c8aae5..19404d2 100644
--- a/internal/mopertest/seed.go
+++ b/internal/mopertest/seed.go
@@ -6,18 +6,28 @@ import (
 	"strconv"
 
 	"github.com/func25/mongofunc/mocom"
-	"go.mongodb.org/mongo-driver/bson/primitive"
 )
 
-type Hero struct {
-	mocom.ID[primitive.ObjectID] `bson:",inline"`
-	Name                         string `bson:"name"`
-	Damage                       int    `bson:"damage"`
-	SkillIds                     []int  `bson:"skillIds"`
-	Omit                         bool   `bson:"omit,omitempty"`
+// weapon
+type Weapon struct {
+	mocom.ID `bson:",inline"`
+	Type     int `json:"type" bson:"type"`
+	Damage   int `json:"damage" bson:"damage"`
+}
+
+func (Weapon) CollName() string {
+	return "Weapons"
 }
 
-const COLLECTION_NAME = "Heroes"
+// hero
+type Hero struct {
+	mocom.ID `bson:",inline"`
+	WeaponID interface{} `bson:"weaponId"`
+	Name     string      `bson:"name"`
+	Damage   int         `bson:"damage"`
+	SkillIds []int       `bson:"skillIds"`
+	Omit     bool        `bson:"omit,omitempty"`
+}
 
 var (
 	ROUND = 10
@@ -50,6 +60,18 @@ func init() {
 //Seed create 1 hero has 1 damage, 2 heroes have 2 damages,... until n (n == 10)
 func Seed(ctx context.Context, n int) error {
 	count := 0
+	weapons := []*Weapon{}
+	for i := 0; i < 3; i++ {
+		x := &Weapon{
+			Type:   i,
+			Damage: 1,
+		}
+		err := mocom.CreateWithID(ctx, x)
+		if err != nil {
+			return err
+		}
+		weapons = append(weapons, x)
+	}
 
 	for i := 0; i < n; i++ {
 		for j := 0; j <= i; j, count = j+1, count+1 {
@@ -58,6 +80,7 @@ func Seed(ctx context.Context, n int) error {
 				Damage:   i + 1,
 				SkillIds: []int{1, 2, 3, 4, 5},
 				Omit:     j == i,
+				WeaponID: weapons[j%3].ID.ID,
 			})
 			if err != nil {
 				return err
@@ -70,5 +93,6 @@ func Seed(ctx context.Context, n int) error {
 
 func Clear(ctx context.Context) error {
 	_, err := mocom.Flush[Hero](ctx)
+	_, err = mocom.Flush[Weapon](ctx)
 	return err
 }
diff --git a/mocom/create.go b/mocom/create.go
index a8ba48b..f9784fa 100644
--- a/mocom/create.go
+++ b/mocom/create.go
@@ -6,11 +6,21 @@ import (
 	"go.mongodb.org/mongo-driver/mongo/options"
 )
 
-func Create[T MongoModel](ctx context.Context, model *T, opts ...*options.InsertOneOptions) (interface{}, error) {
-	col := collWrite((*model).CollName())
+func Create[T Model](ctx context.Context, model T, opts ...*options.InsertOneOptions) (interface{}, error) {
+	col := collWrite(model.CollName())
 	if result, err := col.InsertOne(ctx, model, opts...); err != nil {
 		return nil, err
 	} else {
 		return result.InsertedID, nil
 	}
 }
+
+func CreateWithID[T IDModel](ctx context.Context, model T, opts ...*options.InsertOneOptions) error {
+	col := collWrite(model.CollName())
+	if result, err := col.InsertOne(ctx, model, opts...); err != nil {
+		return err
+	} else {
+		model.SetID(result.InsertedID)
+		return nil
+	}
+}
diff --git a/mocom/find.go b/mocom/find.go
index cdd314e..533ebc5 100644
--- a/mocom/find.go
+++ b/mocom/find.go
@@ -6,7 +6,7 @@ import (
 	"go.mongodb.org/mongo-driver/mongo/options"
 )
 
-func Find[T MongoModel](ctx context.Context, filter interface{}, opts ...*options.FindOptions) (res []T, err error) {
+func Find[T Model](ctx context.Context, filter interface{}, opts ...*options.FindOptions) (res []T, err error) {
 	var t T
 	cur, err := collRead(t.CollName()).Find(ctx, filter, opts...)
 	if err != nil {
@@ -17,7 +17,7 @@ func Find[T MongoModel](ctx context.Context, filter interface{}, opts ...*option
 	return res, err
 }
 
-func FindOne[T MongoModel](ctx context.Context, filter interface{}, opts ...*options.FindOneOptions) (res *T, err error) {
+func FindOne[T Model](ctx context.Context, filter interface{}, opts ...*options.FindOneOptions) (res *T, err error) {
 	res = new(T)
 	cur := collRead((*res).CollName()).FindOne(ctx, filter, opts...)
 	err = cur.Decode(&res)
diff --git a/mocom/mocom.go b/mocom/mocom.go
index 5344ba1..6525d2e 100644
--- a/mocom/mocom.go
+++ b/mocom/mocom.go
@@ -6,39 +6,39 @@ import (
 	"time"
 
 	"github.com/func25/mongofunc/moper"
+	"go.mongodb.org/mongo-driver/bson"
 	"go.mongodb.org/mongo-driver/mongo"
 	"go.mongodb.org/mongo-driver/mongo/options"
 	"go.mongodb.org/mongo-driver/mongo/readconcern"
+	"go.mongodb.org/mongo-driver/mongo/readpref"
 	"go.mongodb.org/mongo-driver/mongo/writeconcern"
 )
 
-func Count[T MongoModel](ctx context.Context, filter interface{}, opts ...*options.CountOptions) (int64, error) {
+func Count[T Model](ctx context.Context, filter interface{}, opts ...*options.CountOptions) (int64, error) {
 	var t T
 	return collRead(t.CollName()).CountDocuments(ctx, filter, opts...)
 }
 
-func EstimatedCount[T MongoModel](ctx context.Context, opts ...*options.EstimatedDocumentCountOptions) (int64, error) {
+func EstimatedCount[T Model](ctx context.Context, opts ...*options.EstimatedDocumentCountOptions) (int64, error) {
 	var t T
 	return collRead(t.CollName()).EstimatedDocumentCount(ctx, opts...)
 }
 
-func Aggregate[T MongoModel](ctx context.Context, req *AggregationRequest[T]) error {
+func Aggregate[T Model](ctx context.Context, req *AggregationRequest[T]) (res []bson.M, err error) {
 	var t T
 	col := db.Collection(t.CollName())
 
 	cursor, err := col.Aggregate(ctx, req.Pipeline, req.Options...)
 	if err != nil {
-		return err
+		return nil, err
 	}
-	// fmt.Println(cursor)
-
-	err = cursor.All(ctx, &req.Result)
+	err = cursor.All(ctx, &res)
 
-	return err
+	return res, err
 }
 
 //Flush clears all records of collection and return number of deleted records
-func Flush[T MongoModel](ctx context.Context) (int64, error) {
+func Flush[T Model](ctx context.Context) (int64, error) {
 	var t T
 	result, err := db.Collection(t.CollName()).DeleteMany(ctx, moper.D{})
 	if err != nil {
@@ -63,14 +63,17 @@ func Tx(ctx context.Context, cfg TransactionConfig) (interface{}, error) {
 	return session.WithTransaction(ctx, cfg.Func, cfg.Options)
 }
 
-// TxOptimal will do the transaction with majority write-concern and local read-concern, client default read pref
+// TxOptimal will do the transaction with majority write-concern
+// snapshot read-concern, primary read preference
+//
+// This should be used when transaction does not contain any read
 func TxOptimal(ctx context.Context, f func(ctx mongo.SessionContext) (interface{}, error)) (interface{}, error) {
 	if client == nil {
 		return nil, errors.New("client is nil, please using mocom to create connection to mongo server or using your own client connection")
 	}
 
 	wc := writeconcern.New(writeconcern.WMajority(), writeconcern.WTimeout(5*time.Second))
-	opts := options.Transaction().SetReadConcern(readconcern.Local()).SetWriteConcern(wc)
+	opts := options.Transaction().SetReadConcern(readconcern.Snapshot()).SetWriteConcern(wc).SetReadPreference(readpref.Primary())
 
 	session, err := client.StartSession()
 	if err != nil {
diff --git a/mocom/model.go b/mocom/model.go
index 03930ae..064dc69 100644
--- a/mocom/model.go
+++ b/mocom/model.go
@@ -1,22 +1,30 @@
 package mocom
 
 import (
-	"go.mongodb.org/mongo-driver/bson"
+	"github.com/func25/mongofunc/moper"
 	"go.mongodb.org/mongo-driver/mongo"
 	"go.mongodb.org/mongo-driver/mongo/options"
 )
 
-type MongoModel interface {
+type Model interface {
 	CollName() string
 }
 
-type ID[T any] struct {
-	ID T `json:"id" bson:"_id,omitempty"`
+type IDModel interface {
+	Model
+	SetID(t interface{})
 }
 
-type AggregationRequest[T MongoModel] struct {
-	Result   []bson.M
-	Pipeline mongo.Pipeline
+type ID struct {
+	ID interface{} `json:"id" bson:"_id,omitempty"`
+}
+
+func (id *ID) SetID(t interface{}) {
+	id.ID = t
+}
+
+type AggregationRequest[T Model] struct {
+	Pipeline []moper.D
 	Options  []*options.AggregateOptions
 }
 
diff --git a/mocom/update.go b/mocom/update.go
index e321e7b..ccfea15 100644
--- a/mocom/update.go
+++ b/mocom/update.go
@@ -7,12 +7,12 @@ import (
 	"go.mongodb.org/mongo-driver/mongo/options"
 )
 
-func UpdateOne[T MongoModel](ctx context.Context, filter interface{}, update interface{}, opts ...*options.UpdateOptions) (*mongo.UpdateResult, error) {
+func UpdateOne[T Model](ctx context.Context, filter interface{}, update interface{}, opts ...*options.UpdateOptions) (*mongo.UpdateResult, error) {
 	var t T
 	return collWrite(t.CollName()).UpdateOne(ctx, filter, update, opts...)
 }
 
-func UpdateAndReturn[T MongoModel](ctx context.Context, filter interface{}, update interface{}, opts ...*options.FindOneAndUpdateOptions) (ptrT *T, err error) {
+func UpdateAndReturn[T Model](ctx context.Context, filter interface{}, update interface{}, opts ...*options.FindOneAndUpdateOptions) (ptrT *T, err error) {
 	ptrT = new(T)
 	res := collWrite((*ptrT).CollName()).FindOneAndUpdate(ctx, filter, update, opts...)
 
@@ -24,7 +24,7 @@ func UpdateAndReturn[T MongoModel](ctx context.Context, filter interface{}, upda
 	return
 }
 
-func UpdateMany[T MongoModel](ctx context.Context, filter interface{}, update interface{}) (*mongo.UpdateResult, error) {
+func UpdateMany[T Model](ctx context.Context, filter interface{}, update interface{}) (*mongo.UpdateResult, error) {
 	var t T
 	return collWrite(t.CollName()).UpdateMany(ctx, filter, update)
 }
diff --git a/moper/aggregate.go b/moper/aggregate.go
new file mode 100644
index 0000000..1c766b0
--- /dev/null
+++ b/moper/aggregate.go
@@ -0,0 +1,21 @@
+package moper
+
+func (d D) Match(pairs ...P) D {
+	return d.Equal("$match", toPair(pairs))
+}
+
+func (d D) MatchD(pair D) D {
+	return d.Equal("$match", pair)
+}
+
+func (d D) Group(pairs ...P) D {
+	return d.Equal("$group", toPair(pairs))
+}
+
+func (d D) GroupD(pair D) D {
+	return d.Equal("$group", pair)
+}
+
+func (d D) Sum(fieldName string) D {
+	return d.Equal("$sum", "$"+fieldName)
+}
diff --git a/moper/aggregate_lookup.go b/moper/aggregate_lookup.go
new file mode 100644
index 0000000..dab9128
--- /dev/null
+++ b/moper/aggregate_lookup.go
@@ -0,0 +1,50 @@
+package moper
+
+type LU struct {
+	d D
+}
+
+// Specifies the foreign collection in the same database to join to the local collection.
+// The foreign collection cannot be sharded
+func (l *LU) From(collName string) *LU {
+	l.d = l.d.Equal("from", collName)
+	return l
+}
+
+// Specifies the local documents' localField to perform an equality match with the foreign documents' foreignField.
+func (l *LU) LocalField(field string) *LU {
+	l.d = l.d.Equal("localField", field)
+	return l
+}
+
+// Specifies the foreign documents' foreignField to perform an equality match with the local documents' localField.
+// If a foreign document does not contain a foreignField value, the $lookup uses a null value for the match.
+func (l *LU) ForeignField(field string) *LU {
+	l.d = l.d.Equal("foreignField", field)
+	return l
+}
+
+func (l *LU) Custom(p P) *LU {
+	l.d = l.d.Equal(p.K, p.V)
+	return l
+}
+
+func (l *LU) D() D {
+	return D{}.Equal("$lookup", l.d)
+}
+
+// Optional, Specifies the variables to use in the pipeline stages.
+// Use the variable expressions to access the document fields that are input to the pipeline.
+// func (l *LookUp) Let(collName string) *LookUp {
+// 	l.d = l.d.Equal("let", collName)
+// 	return l
+// }
+
+func (l *LU) As(field string) *LU {
+	l.d = l.d.Equal("as", field)
+	return l
+}
+
+func (d D) LookUp() *LU {
+	return &LU{d: d}
+}