plan: implement Next for TableNilPlan

plan/plans/from.go

@@ -43,7 +43,8 @@ var (
 
 // TableNilPlan iterates rows but does nothing, e.g. SELECT 1 FROM t;
 type TableNilPlan struct {
-	T table.Table
+	T    table.Table
+	iter kv.Iterator
 }
 
 // Explain implements the plan.Plan interface.
@@ -97,14 +98,42 @@ func (r *TableNilPlan) Do(ctx context.Context, f plan.RowIterFunc) error {
 
 // Next implements plan.Plan Next interface.
 func (r *TableNilPlan) Next(ctx context.Context) (row *plan.Row, err error) {
+	if r.iter == nil {
+		var txn kv.Transaction
+		txn, err = ctx.GetTxn(false)
+		if err != nil {
+			return nil, errors.Trace(err)
+		}
+		r.iter, err = txn.Seek([]byte(r.T.FirstKey()), nil)
+		if err != nil {
+			return nil, errors.Trace(err)
+		}
+	}
+	if !r.iter.Valid() || !strings.HasPrefix(r.iter.Key(), r.T.KeyPrefix()) {
+		return
+	}
+	id, err := util.DecodeHandleFromRowKey(r.iter.Key())
+	if err != nil {
+		return nil, errors.Trace(err)
+	}
+	rk := r.T.RecordKey(id, nil)
+	row = &plan.Row{}
+	r.iter, err = kv.NextUntil(r.iter, util.RowKeyPrefixFilter(rk))
 	return
 }
 
 // Close implements plan.Plan Close interface.
 func (r *TableNilPlan) Close() error {
+	r.iter.Close()
 	return nil
 }
 
+// UseNext implements NextPlan interface
+func (r *TableNilPlan) UseNext() bool {
+	log.Warn("use next")
+	return true
+}
+
 // TableDefaultPlan iterates rows from a table, in general case
 // it performs a full table scan, but using Filter function,
 // it will return a new IndexPlan if an index is found in Filter function.

plan/plans/from_test.go

@@ -109,8 +109,14 @@ func (p *testFromSuit) TestTableNilPlan(c *C) {
 		T: p.tbl,
 	}
 	var ids []int64
-	nilPlan.Do(p, func(id interface{}, data []interface{}) (bool, error) {
-		ids = append(ids, id.(int64))
+	rset := rsets.Recordset{
+		Plan: nilPlan,
+		Ctx:  p,
+	}
+	var id int64
+	rset.Do(func(data []interface{}) (bool, error) {
+		id++
+		ids = append(ids, id)
 		return true, nil
 	})
 	c.Assert(reflect.DeepEqual(ids, []int64{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}), Equals, true)