Add option to add ALLOW FILTERING to the update query (#290)

qb/update.go

@@ -37,6 +37,7 @@ type UpdateBuilder struct {
 	_if         _if
 	using       using
 	exists      bool
+	allowFiltering    bool
 }
 
 // Update returns a new UpdateBuilder with the given table name.
@@ -72,6 +73,10 @@ func (b *UpdateBuilder) ToCql() (stmt string, names []string) {
 		cql.WriteString("IF EXISTS ")
 	}
 
+	if b.allowFiltering {
+		cql.WriteString("ALLOW FILTERING ")
+	}
+
 	stmt = cql.String()
 	return
 }
@@ -196,6 +201,12 @@ func (b *UpdateBuilder) AddFunc(column string, fn *Func) *UpdateBuilder {
 	return b.addValue(column, fn)
 }
 
+// AllowFiltering sets a ALLOW FILTERING clause on the query.
+func (b *UpdateBuilder) AllowFiltering() *UpdateBuilder {
+	b.allowFiltering = true
+	return b
+}
+
 func (b *UpdateBuilder) addValue(column string, value value) *UpdateBuilder {
 	b.assignments = append(b.assignments, assignment{
 		column:      column,