Optimistic locking

field.go

@@ -18,6 +18,10 @@ type DateFields struct {
 	UpdatedAt time.Time `json:"updated_at" bson:"updated_at"`
 }
 
+type VersionField struct {
+	Version int `json:"version" bson:"version"`
+}
+
 // PrepareID method prepares the ID value to be used for filtering
 // e.g convert hex-string ID value to bson.ObjectId
 func (f *IDField) PrepareID(id interface{}) (interface{}, error) {
@@ -39,6 +43,21 @@ func (f *IDField) SetID(id interface{}) {
 	f.ID = id.(primitive.ObjectID)
 }
 
+// GetVersion returns the model version field
+func (f *VersionField) GetVersion() interface{} {
+	return f.Version
+}
+
+// GetVersionFieldName returns the field name holding the version field (has to match the bson tag)
+func (f *VersionField) GetVersionFieldName() string {
+	return "version"
+}
+
+// SetVersion returns the model version field
+func (f *VersionField) IncrementVersion() {
+	f.Version++
+}
+
 //--------------------------------
 // DateField methods
 //--------------------------------
@@ -51,7 +70,7 @@ func (f *DateFields) Creating() error {
 	return nil
 }
 
-// Saving hook is used here to set the `updated_at` field 
+// Saving hook is used here to set the `updated_at` field
 // value when creating or updateing a model.
 // TODO: get context as param the next version(4).
 func (f *DateFields) Saving() error {

model.go

@@ -26,10 +26,17 @@ type Model interface {
 	SetID(id interface{})
 }
 
+type Versionable interface {
+	GetVersion() interface{}
+	GetVersionFieldName() string
+	IncrementVersion()
+}
+
 // DefaultModel struct contains a model's default fields.
 type DefaultModel struct {
-	IDField    `bson:",inline"`
-	DateFields `bson:",inline"`
+	IDField      `bson:",inline"`
+	DateFields   `bson:",inline"`
+	VersionField `bson:",inline"`
 }
 
 // Creating function calls the inner fields' defined hooks

model_test.go

@@ -1,10 +1,11 @@
 package mgm_test
 
 import (
+	"testing"
+
 	"github.com/kamva/mgm/v3/internal/util"
 	"github.com/stretchr/testify/require"
 	"go.mongodb.org/mongo-driver/bson/primitive"
-	"testing"
 )
 
 func TestPrepareInvalidId(t *testing.T) {
@@ -23,3 +24,11 @@ func TestPrepareId(t *testing.T) {
 	require.Equal(t, val.(primitive.ObjectID), id)
 	util.AssertErrIsNil(t, err)
 }
+
+func TestVersion(t *testing.T) {
+	d := &Doc{}
+	require.Equal(t, 0, d.GetVersion())
+	require.Equal(t, "version", d.GetVersionFieldName())
+	d.IncrementVersion()
+	require.Equal(t, 1, d.GetVersion())
+}

operation.go

@@ -2,6 +2,9 @@ package mgm
 
 import (
 	"context"
+	"fmt"
+	"time"
+
 	"github.com/kamva/mgm/v3/field"
 	"go.mongodb.org/mongo-driver/bson"
 	"go.mongodb.org/mongo-driver/mongo/options"
@@ -35,12 +38,44 @@ func update(ctx context.Context, c *Collection, model Model, opts ...*options.Up
 		return err
 	}
 
-	res, err := c.UpdateOne(ctx, bson.M{field.ID: model.GetID()}, bson.M{"$set": model}, opts...)
+	query := bson.M{field.ID: model.GetID()}
+	modelVersionable, isVersionable := model.(Versionable)
+	var currentVersion interface{}
+	if isVersionable {
+		currentVersion = modelVersionable.GetVersion()
+
+		//Handle adding versionning for documents that were created without it
+		//In this case, the version field would be of zero value and not exist in the DB
+		//Add $or exists false in the query condition for this case
+		isCurrentVersionZero := false
+		switch c := currentVersion.(type) {
+		case string:
+			isCurrentVersionZero = c == ""
+		case int:
+			isCurrentVersionZero = c == 0
+		case time.Time:
+			isCurrentVersionZero = c.IsZero()
+		}
+
+		if isCurrentVersionZero {
+			query["$or"] = bson.A{bson.M{modelVersionable.GetVersionFieldName(): currentVersion}, bson.M{modelVersionable.GetVersionFieldName(): bson.M{"$exists": false}}}
+		} else {
+			query[modelVersionable.GetVersionFieldName()] = currentVersion
+		}
+
+		modelVersionable.IncrementVersion()
+	}
+
+	res, err := c.UpdateOne(ctx, query, bson.M{"$set": model}, opts...)
 
 	if err != nil {
 		return err
 	}
 
+	if isVersionable && res.MatchedCount == 0 {
+		return fmt.Errorf("versioning error : document %v %v with version %v could not be found", c.Name(), model.GetID(), currentVersion)
+	}
+
 	return callToAfterUpdateHooks(ctx, res, model)
 }