add offset step to query builder (#1049)

Summary:
Pull Request resolved: https://github.com/facebookexternal/fbc/pull/1049

Useful for real paging

Reviewed By: noamsch

Differential Revision: D16003607

fbshipit-source-id: 6a85d0e3d71a2582bc3cd8f1d66748dda4f2a10e

entc/gen/template/builder/query.tmpl

@@ -10,10 +10,11 @@
 // {{ $builder }} is the builder for querying {{ pascal $.Name }} entities.
 type {{ $builder }} struct {
 	config
-	limit *int
-	order  []Order
-	unique []string
-	predicates []ent.Predicate
+	limit		*int
+	offset		*int
+	order		[]Order
+	unique		[]string
+	predicates 	[]ent.Predicate
 	// intermediate queries.
 	sql     *sql.Selector
 	gremlin *dsl.Traversal
@@ -31,6 +32,12 @@ func ({{ $receiver }} *{{ $builder }}) Limit(limit int) *{{ $builder }} {
 	return {{ $receiver }}
 }
 
+// Offset adds an offset step to the query.
+func ({{ $receiver }} *{{ $builder }}) Offset(offset int) *{{ $builder }} {
+	{{ $receiver }}.offset = &offset
+	return {{ $receiver }}
+}
+
 // Order adds an order step to the query.
 func ({{ $receiver }} *{{ $builder }}) Order(o ...Order) *{{ $builder }} {
 	{{ $receiver }}.order = append({{ $receiver }}.order, o...)