Use the only field type elem to check the content

go.mod

@@ -5,7 +5,7 @@ go 1.13
 require (
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.1
-	github.com/stretchr/testify v1.6.1
+	github.com/stretchr/testify v1.7.0
 	github.com/valyala/bytebufferpool v1.0.0
-	go.mongodb.org/mongo-driver v1.4.3
+	go.mongodb.org/mongo-driver v1.4.6
 )

go.sum

@@ -75,11 +75,13 @@ github.com/sirupsen/logrus v1.4.2/go.mod h1:tLMulIdttU9McNUspp0xgXVQah82FyeX6Mwd
 github.com/spf13/cobra v0.0.3/go.mod h1:1l0Ry5zgKvJasoi3XT1TypsSe7PqH0Sj9dhYf7v3XqQ=
 github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/objx v0.1.1 h1:2vfRuCMp5sSVIDSqO8oNnWJq7mPa6KVP3iPIwFBuy8A=
 github.com/stretchr/objx v0.1.1/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
-github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
 github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/tidwall/pretty v1.0.0 h1:HsD+QiTn7sK6flMKIvNmpqz1qrpP3Ps6jOKIKMooyg4=
 github.com/tidwall/pretty v1.0.0/go.mod h1:XNkn88O1ChpSDQmQeStsy+sBenx6DDtFZJxhVysOjyk=
 github.com/valyala/bytebufferpool v1.0.0 h1:GqA5TC/0021Y/b9FG4Oi9Mr3q7XYx6KllzawFIhcdPw=
@@ -88,8 +90,8 @@ github.com/xdg/scram v0.0.0-20180814205039-7eeb5667e42c h1:u40Z8hqBAAQyv+vATcGgV
 github.com/xdg/scram v0.0.0-20180814205039-7eeb5667e42c/go.mod h1:lB8K/P019DLNhemzwFU4jHLhdvlE6uDZjXFejJXr49I=
 github.com/xdg/stringprep v0.0.0-20180714160509-73f8eece6fdc h1:n+nNi93yXLkJvKwXNP9d55HC7lGK4H/SRcwB5IaUZLo=
 github.com/xdg/stringprep v0.0.0-20180714160509-73f8eece6fdc/go.mod h1:Jhud4/sHMO4oL310DaZAKk9ZaJ08SJfe+sJh0HrGL1Y=
-go.mongodb.org/mongo-driver v1.4.3 h1:moga+uhicpVshTyaqY9L23E6QqwcHRUv1sqyOsoyOO8=
-go.mongodb.org/mongo-driver v1.4.3/go.mod h1:WcMNYLx/IlOxLe6JRJiv2uXuCz6zBLndR4SoGjYphSc=
+go.mongodb.org/mongo-driver v1.4.6 h1:rh7GdYmDrb8AQSkF8yteAus8qYOgOASWDOv1BWqBXkU=
+go.mongodb.org/mongo-driver v1.4.6/go.mod h1:WcMNYLx/IlOxLe6JRJiv2uXuCz6zBLndR4SoGjYphSc=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20190422162423-af44ce270edf/go.mod h1:WFFai1msRO1wXaEeE5yQxYXgSfI8pQAWXbQop6sCtWE=

mongox/base/reset.go

@@ -6,7 +6,7 @@ import (
 )
 
 // Reset function creates new zero object for the target pointer
-func Reset(target interface{}) {
+func Reset(target interface{}) (created bool) {
 
 	type resetter interface {
 		Reset()
@@ -15,7 +15,7 @@ func Reset(target interface{}) {
 	resettable, canReset := target.(resetter)
 	if canReset {
 		resettable.Reset()
-		return
+		return false
 	}
 
 	v := reflect.ValueOf(target)
@@ -27,4 +27,6 @@ func Reset(target interface{}) {
 	zero := reflect.Zero(t)
 
 	v.Elem().Set(zero)
+
+	return true
 }

mongox/database/database.go

@@ -126,8 +126,12 @@ func (d *Database) createAggregateLoad(target interface{}, composed *query.Query
 		pipeline = append(pipeline, primitive.M{"$limit": *composed.Limiter()})
 	}
 
-	el := reflect.ValueOf(target).Elem()
+	el := reflect.ValueOf(target)
 	elType := el.Type()
+	if elType.Kind() == reflect.Ptr {
+		elType = elType.Elem()
+	}
+
 	numField := elType.NumField()
 	preloads, _ := composed.Preloader()
 
@@ -191,17 +195,20 @@ func (d *Database) createAggregateLoad(target interface{}, composed *query.Query
 				continue
 			}
 
-			isSlice := el.Field(i).Kind() == reflect.Slice
+			field := elType.Field(i)
+			fieldType := field.Type
 
-			typ := el.Field(i).Type()
-			if typ.Kind() == reflect.Slice {
-				typ = typ.Elem()
+			isSlice := fieldType.Kind() == reflect.Slice
+			if isSlice {
+				fieldType = fieldType.Elem()
 			}
-			if typ.Kind() != reflect.Ptr {
+
+			isPtr := fieldType.Kind() != reflect.Ptr
+			if isPtr {
 				panic(fmt.Errorf("preload field should have ptr type"))
 			}
 
-			lookupCollection := d.GetCollectionOf(reflect.Zero(typ).Interface())
+			lookupCollection := d.GetCollectionOf(reflect.Zero(fieldType).Interface())
 			lookupVars := primitive.M{"selector": "$" + localField}
 			lookupPipeline := primitive.A{
 				primitive.M{"$match": primitive.M{"$expr": primitive.M{"$eq": primitive.A{"$" + foreignField, "$$selector"}}}},

mongox/database/loadarray.go

@@ -70,32 +70,45 @@ func (d *Database) LoadArray(target interface{}, filters ...interface{}) (err er
 		return
 	}
 
-	for i = 0; result.Next(ctx); {
+	for i = 0; result.Next(ctx); i++ {
 
 		var elem interface{}
 
-		if targetSliceV.Len() == i {
+		if i == targetSliceV.Len() {
 			value := reflect.New(targetSliceElemT.Elem())
-			err = result.Decode(value.Interface())
 			elem = value.Interface()
-			if err == nil {
-				targetSliceV = reflect.Append(targetSliceV, value)
+
+			err = composed.OnCreate().Invoke(ctx, elem)
+			if err != nil {
+				return
 			}
+
+			err = result.Decode(elem)
+			if err != nil {
+				return
+			}
+
+			targetSliceV = reflect.Append(targetSliceV, value)
 		} else {
 			elem = targetSliceV.Index(i).Interface()
-			base.Reset(elem)
-			err = result.Decode(elem)
+
+			if created := base.Reset(elem); created {
+				err = composed.OnCreate().Invoke(ctx, elem)
 			}
 			if err != nil {
 				return
 			}
 
+			err = result.Decode(elem)
+			if err != nil {
+				return
+			}
+		}
+
 		err = composed.OnDecode().Invoke(ctx, elem)
 		if err != nil {
 			return
 		}
-
-		i++
 	}
 
 	targetSliceV = targetSliceV.Slice(0, i)

mongox/database/loadone.go

@@ -56,7 +56,12 @@ func (d *Database) LoadOne(target interface{}, filters ...interface{}) (err erro
 		return mongox.ErrNoDocuments
 	}
 
-	base.Reset(target)
+	if created := base.Reset(target); created {
+		err = composed.OnCreate().Invoke(ctx, target)
+	}
+	if err != nil {
+		return
+	}
 
 	err = result.Decode(target)
 	if err != nil {

mongox/database/loadstream.go

@@ -30,7 +30,7 @@ func (d *Database) LoadStream(target interface{}, filters ...interface{}) (loade
 		return
 	}
 
-	loader = &StreamLoader{cur: cursor, ctx: ctx, target: target, query: composed}
+	loader = &StreamLoader{cur: cursor, ctx: ctx, query: composed}
 
 	return
 }

mongox/database/streamloader.go

@@ -13,18 +13,17 @@ type StreamLoader struct {
 	cur   *mongox.Cursor
 	query *query.Query
 	ctx   context.Context
-	target interface{}
 }
 
-// DecodeNext loads next documents to a target or returns an error
-func (l *StreamLoader) DecodeNext() (err error) {
+// DecodeNextMsg decodes the next document to an interface or returns an error
+func (l *StreamLoader) DecodeNextMsg(i interface{}) (err error) {
 
 	err = l.Next()
 	if err != nil {
 		return
 	}
 
-	err = l.Decode()
+	err = l.DecodeMsg(i)
 	if err != nil {
 		return
 	}
@@ -32,17 +31,22 @@ func (l *StreamLoader) DecodeNext() (err error) {
 	return
 }
 
-// Decode function decodes the current cursor document into the target
-func (l *StreamLoader) Decode() (err error) {
+// DecodeMsg decodes the current cursor document into an interface
+func (l *StreamLoader) DecodeMsg(i interface{}) (err error) {
 
-	base.Reset(l.target)
-
-	err = l.cur.Decode(l.target)
+	if created := base.Reset(i); created {
+		err = l.query.OnDecode().Invoke(l.ctx, i)
+	}
 	if err != nil {
 		return
 	}
 
-	err = l.query.OnDecode().Invoke(l.ctx, l.target)
+	err = l.cur.Decode(i)
+	if err != nil {
+		return
+	}
+
+	err = l.query.OnDecode().Invoke(l.ctx, i)
 	if err != nil {
 		return
 	}
@@ -66,15 +70,16 @@ func (l *StreamLoader) Next() (err error) {
 	return
 }
 
+// Cursor returns the underlying cursor
 func (l *StreamLoader) Cursor() (cursor *mongox.Cursor) {
 	return l.cur
 }
 
-// Close cursor
+// Close stream loader and the underlying cursor
 func (l *StreamLoader) Close() (err error) {
 
 	closerr := l.cur.Close(l.ctx)
-	invokerr := l.query.OnClose().Invoke(l.ctx, l.target)
+	invokerr := l.query.OnClose().Invoke(l.ctx, nil)
 
 	if closerr != nil {
 		err = closerr
@@ -89,6 +94,7 @@ func (l *StreamLoader) Close() (err error) {
 	return
 }
 
+// Err returns the last error
 func (l *StreamLoader) Err() (err error) {
 	return l.cur.Err()
 }

mongox/mongox.go

@@ -35,8 +35,8 @@ type Database interface {
 // StreamLoader is a interface to control database cursor
 type StreamLoader interface {
 	Cursor() (cursor *Cursor)
-	DecodeNext() (err error)
-	Decode() (err error)
+	DecodeNextMsg(i interface{}) (err error)
+	DecodeMsg(i interface{}) (err error)
 	Next() (err error)
 	Close() (err error)
 	Err() (err error)

mongox/query/query.go

@@ -17,6 +17,7 @@ type Query struct {
 	updater   Updater
 	ondecode  Callbacks
 	onclose   Callbacks
+	oncreate  Callbacks
 }
 
 // And function pushes the elem query to the $and array of the query
@@ -118,10 +119,16 @@ func (q *Query) OnDecode() (callbacks Callbacks) {
 	return q.ondecode
 }
 
+// OnClose callback is called after the mongox ends a loading procedure
 func (q *Query) OnClose() (callbacks Callbacks) {
 	return q.onclose
 }
 
+// OnCreate callback is called if the mongox creates a new document instance during loading
+func (q *Query) OnCreate() (callbacks Callbacks) {
+	return q.onclose
+}
+
 // Empty checks the query for any content
 func (q *Query) Empty() (isEmpty bool) {
 	return len(q.m) == 0