Added AscendEqual and DescendEqual

AscendEqual and DescendEqual return only the items that equal
a specified value.

Closes #26

README.md

@@ -148,7 +148,9 @@ err := tx.Ascend("", func(key, value string) bool{
 })
 ```
 
-There is also `AscendGreaterOrEqual`, `AscendLessThan`, `AscendRange`, `Descend`, `DescendLessOrEqual`, `DescendGreaterThan`, and `DescendRange`. Please see the [documentation](https://godoc.org/github.com/tidwall/buntdb) for more information on these functions.
+There is also `AscendGreaterOrEqual`, `AscendLessThan`, `AscendRange`, `AscendEqual`, `Descend`, `DescendLessOrEqual`, `DescendGreaterThan`, `DescendRange`, and `DescendEqual`. Please see the [documentation](https://godoc.org/github.com/tidwall/buntdb) for more information on these functions.
+
+
 
 
 ## Custom Indexes

buntdb.go

@@ -1185,6 +1185,7 @@ type dbItemOpts struct {
 type dbItem struct {
 	key, val string      // the binary key and value
 	opts     *dbItemOpts // optional meta information
+	keyless  bool        // keyless item for scanning
 }
 
 func appendArray(buf []byte, count int) []byte {
@@ -1278,6 +1279,11 @@ func (dbi *dbItem) Less(item btree.Item, ctx interface{}) bool {
 		}
 	}
 	// Always fall back to the key comparison. This creates absolute uniqueness.
+	if dbi.keyless {
+		return false
+	} else if dbi2.keyless {
+		return true
+	}
 	return dbi.key < dbi2.key
 }
 
@@ -1507,6 +1513,10 @@ func (tx *Tx) scan(desc, gt, lt bool, index, start, stop string,
 		} else {
 			itemA = &dbItem{val: start}
 			itemB = &dbItem{val: stop}
+			if desc {
+				itemA.keyless = true
+				itemB.keyless = true
+			}
 		}
 	}
 	// execute the scan on the underlying tree.
@@ -1709,6 +1719,62 @@ func (tx *Tx) DescendRange(index, lessOrEqual, greaterThan string,
 	)
 }
 
+// AscendEqual calls the iterator for every item in the database that equals
+// pivot, until iterator returns false.
+// When an index is provided, the results will be ordered by the item values
+// as specified by the less() function of the defined index.
+// When an index is not provided, the results will be ordered by the item key.
+// An invalid index will return an error.
+func (tx *Tx) AscendEqual(index, pivot string,
+	iterator func(key, value string) bool) error {
+	var err error
+	var less func(a, b string) bool
+	if index != "" {
+		less, err = tx.GetLess(index)
+		if err != nil {
+			return err
+		}
+	}
+	return tx.AscendGreaterOrEqual(index, pivot, func(key, value string) bool {
+		if less == nil {
+			if key != pivot {
+				return false
+			}
+		} else if less(pivot, value) {
+			return false
+		}
+		return iterator(key, value)
+	})
+}
+
+// DescendEqual calls the iterator for every item in the database that equals
+// pivot, until iterator returns false.
+// When an index is provided, the results will be ordered by the item values
+// as specified by the less() function of the defined index.
+// When an index is not provided, the results will be ordered by the item key.
+// An invalid index will return an error.
+func (tx *Tx) DescendEqual(index, pivot string,
+	iterator func(key, value string) bool) error {
+	var err error
+	var less func(a, b string) bool
+	if index != "" {
+		less, err = tx.GetLess(index)
+		if err != nil {
+			return err
+		}
+	}
+	return tx.DescendLessOrEqual(index, pivot, func(key, value string) bool {
+		if less == nil {
+			if key != pivot {
+				return false
+			}
+		} else if less(value, pivot) {
+			return false
+		}
+		return iterator(key, value)
+	})
+}
+
 // rect is used by Intersects
 type rect struct {
 	min, max []float64

buntdb_test.go

@@ -495,6 +495,110 @@ func TestDeleteAll(t *testing.T) {
 	}
 }
 
+func TestAscendEqual(t *testing.T) {
+	db := testOpen(t)
+	defer testClose(db)
+	if err := db.Update(func(tx *Tx) error {
+		for i := 0; i < 300; i++ {
+			_, _, err := tx.Set(fmt.Sprintf("key:%05dA", i), fmt.Sprintf("%d", i+1000), nil)
+			if err != nil {
+				return err
+			}
+			_, _, err = tx.Set(fmt.Sprintf("key:%05dB", i), fmt.Sprintf("%d", i+1000), nil)
+			if err != nil {
+				return err
+			}
+		}
+		return tx.CreateIndex("num", "*", IndexInt)
+	}); err != nil {
+		t.Fatal(err)
+	}
+	var res []string
+	if err := db.View(func(tx *Tx) error {
+		return tx.AscendEqual("", "key:00055A", func(key, value string) bool {
+			res = append(res, key)
+			return true
+		})
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if len(res) != 1 {
+		t.Fatalf("expected %v, got %v", 1, len(res))
+	}
+	if res[0] != "key:00055A" {
+		t.Fatalf("expected %v, got %v", "key:00055A", res[0])
+	}
+	res = nil
+	if err := db.View(func(tx *Tx) error {
+		return tx.AscendEqual("num", "1125", func(key, value string) bool {
+			res = append(res, key)
+			return true
+		})
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if len(res) != 2 {
+		t.Fatalf("expected %v, got %v", 2, len(res))
+	}
+	if res[0] != "key:00125A" {
+		t.Fatalf("expected %v, got %v", "key:00125A", res[0])
+	}
+	if res[1] != "key:00125B" {
+		t.Fatalf("expected %v, got %v", "key:00125B", res[1])
+	}
+}
+func TestDescendEqual(t *testing.T) {
+	db := testOpen(t)
+	defer testClose(db)
+	if err := db.Update(func(tx *Tx) error {
+		for i := 0; i < 300; i++ {
+			_, _, err := tx.Set(fmt.Sprintf("key:%05dA", i), fmt.Sprintf("%d", i+1000), nil)
+			if err != nil {
+				return err
+			}
+			_, _, err = tx.Set(fmt.Sprintf("key:%05dB", i), fmt.Sprintf("%d", i+1000), nil)
+			if err != nil {
+				return err
+			}
+		}
+		return tx.CreateIndex("num", "*", IndexInt)
+	}); err != nil {
+		t.Fatal(err)
+	}
+	var res []string
+	if err := db.View(func(tx *Tx) error {
+		return tx.DescendEqual("", "key:00055A", func(key, value string) bool {
+			res = append(res, key)
+			return true
+		})
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if len(res) != 1 {
+		t.Fatalf("expected %v, got %v", 1, len(res))
+	}
+	if res[0] != "key:00055A" {
+		t.Fatalf("expected %v, got %v", "key:00055A", res[0])
+	}
+	res = nil
+	if err := db.View(func(tx *Tx) error {
+		return tx.DescendEqual("num", "1125", func(key, value string) bool {
+			res = append(res, key)
+			return true
+		})
+	}); err != nil {
+		t.Fatal(err)
+	}
+	if len(res) != 2 {
+		t.Fatalf("expected %v, got %v", 2, len(res))
+	}
+	if res[0] != "key:00125B" {
+		t.Fatalf("expected %v, got %v", "key:00125B", res[0])
+	}
+	if res[1] != "key:00125A" {
+		t.Fatalf("expected %v, got %v", "key:00125A", res[1])
+	}
+}
 func TestVariousTx(t *testing.T) {
 	db := testOpen(t)
 	defer testClose(db)