leveldb query: limit + offset

datastore.go

@@ -79,9 +79,21 @@ func (d *datastore) Query(q dsq.Query) (*dsq.Results, error) {
 	}
 	i := d.DB.NewIterator(rnge, nil)
 
+	// offset
+	if q.Offset > 0 {
+		for j := 0; j < q.Offset; j++ {
+			i.Next()
+		}
+	}
+
 	var es []dsq.Entry
 	for i.Next() {
 
+		// limit
+		if q.Limit > 0 && len(es) >= q.Limit {
+			break
+		}
+
 		k := ds.NewKey(string(i.Key())).String()
 		e := dsq.Entry{Key: k}
 
@@ -98,10 +110,15 @@ func (d *datastore) Query(q dsq.Query) (*dsq.Results, error) {
 		return nil, err
 	}
 
+	// Now, apply remaining pieces.
+	q2 := q
+	q2.Offset = 0 // already applied
+	q2.Limit = 0  // already applied
 	// TODO: make this async with:
 	// qr := dsq.ResultsWithEntriesChan(q, ch)
 	qr := dsq.ResultsWithEntries(q, es)
-	qr = q.ApplyTo(qr)
+	qr = q2.ApplyTo(qr)
+	qr.Query = q // set it back
 	return qr, nil
 }
 

ds_test.go

@@ -59,21 +59,35 @@ func TestQuery(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	expect := []string{
+	expectMatches(t, []string{
 		"/a/b",
 		"/a/b/c",
 		"/a/b/d",
 		"/a/c",
 		"/a/d",
+	}, rs.AllEntries())
+
+	// test offset and limit
+
+	rs, err = d.Query(dsq.Query{Prefix: "/a/", Offset: 2, Limit: 2})
+	if err != nil {
+		t.Fatal(err)
 	}
 
-	re := rs.AllEntries()
-	if len(re) != len(expect) {
-		t.Error("not enough", expect, re)
+	expectMatches(t, []string{
+		"/a/b/d",
+		"/a/c",
+	}, rs.AllEntries())
+
+}
+
+func expectMatches(t *testing.T, expect []string, actual []dsq.Entry) {
+	if len(actual) != len(expect) {
+		t.Error("not enough", expect, actual)
 	}
 	for _, k := range expect {
 		found := false
-		for _, e := range re {
+		for _, e := range actual {
 			if e.Key == k {
 				found = true
 			}