Add preloader filter

Fix pipeline structure


Fix preloader logic

mongox/query/compose.go

@@ -30,6 +30,7 @@ func Push(q *Query, f interface{}) bool {
 	ok = ok || applySort(q, f)
 	ok = ok || applySkip(q, f)
 	ok = ok || applyProtection(q, f)
+	ok = ok || applyPreloader(q, f)
 
 	return ok
 }
@@ -108,3 +109,13 @@ func applyProtection(q *Query, f interface{}) bool {
 
 	return true
 }
+
+func applyPreloader(q *Query, f interface{}) bool {
+
+	if f, ok := f.(Preloader); ok {
+		q.preloader = f
+		return true
+	}
+
+	return false
+}

mongox/query/preload.go

@@ -0,0 +1,17 @@
+package query
+
+// Preloader is a filter to skip the result
+type Preloader interface {
+	Preload() []string
+}
+
+// Preload is a simple implementation of the Skipper filter
+type Preload []string
+
+var _ Preloader = Preload{}
+
+// Preload returns a preload list
+func (l Preload) Preload() []string {
+
+	return Preload(l)
+}

mongox/query/query.go

@@ -8,10 +8,11 @@ import (
 
 // Query is an enchanched bson.M map
 type Query struct {
-	m       bson.M
-	limiter Limiter
-	sorter  Sorter
-	skipper Skipper
+	m         bson.M
+	limiter   Limiter
+	sorter    Sorter
+	skipper   Skipper
+	preloader Preloader
 }
 
 // And function pushes the elem query to the $and array of the query
@@ -63,6 +64,22 @@ func (q *Query) Skipper() *int64 {
 	return q.skipper.Skip()
 }
 
+// Preloader is a preloader list for a query
+func (q *Query) Preloader() (empty bool, preloader []string) {
+
+	if q.preloader == nil {
+		return false, nil
+	}
+
+	preloader = q.preloader.Preload()
+
+	if len(preloader) == 0 {
+		return false, nil
+	}
+
+	return true, preloader
+}
+
 // Empty checks the query for any content
 func (q *Query) Empty() bool {