multi value indexes

README.md

@@ -33,6 +33,7 @@ Features
 - [Spatial indexing](#spatial-indexes) for up to 20 dimensions; Useful for Geospatial data
 - Index fields inside [JSON](#json-indexes) documents
 - Create [custom indexes](#custom-indexes) for any data type
+- Support for [multi value indexes](#multi-value-index); Similar to a SQL multi column index
 - [Built-in types](#built-in-types) that are easy to get up & running; String, Uint, Int, Float
 - Flexible [iteration](#iterating) of data; ascending, descending, and ranges
 - [Durable append-only file](#append-only-file) format for persistence. 
@@ -411,6 +412,41 @@ Order by age range 30-50
 1: {"name":{"first":"Tom","last":"Johnson"},"age":38}
 2: {"name":{"first":"Janet","last":"Prichard"},"age":47}
 ```
+## Multi Value Index
+With BuntDB it's possible to join multiple values on a single index. 
+This is similar to a [multi column index](http://dev.mysql.com/doc/refman/5.7/en/multiple-column-indexes.html) in a traditional SQL database.
+
+In this example we are creating a multi value index on "name.last" and "age":
+
+```go
+	db, _ := buntdb.Open(":memory:")
+	db.CreateIndex("last_name_age", "*", buntdb.IndexJSON("name.last"), buntdb.IndexJSON("age"))
+	db.Update(func(tx *buntdb.Tx) error {
+		tx.Set("1", `{"name":{"first":"Tom","last":"Johnson"},"age":38}`, nil)
+		tx.Set("2", `{"name":{"first":"Janet","last":"Prichard"},"age":47}`, nil)
+		tx.Set("3", `{"name":{"first":"Carol","last":"Anderson"},"age":52}`, nil)
+		tx.Set("4", `{"name":{"first":"Alan","last":"Cooper"},"age":28}`, nil)
+		tx.Set("5", `{"name":{"first":"Sam","last":"Anderson"},"age":51}`, nil)
+		tx.Set("6", `{"name":{"first":"Melinda","last":"Prichard"},"age":44}`, nil)
+		return nil
+	})
+	db.View(func(tx *buntdb.Tx) error {
+		tx.Ascend("last_name_age", func(key, value string) bool {
+			fmt.Printf("%s: %s\n", key, value)
+			return true
+		})
+		return nil
+	})
+
+	// Output:
+	// 5: {"name":{"first":"Sam","last":"Anderson"},"age":51}
+	// 3: {"name":{"first":"Carol","last":"Anderson"},"age":52}
+	// 4: {"name":{"first":"Alan","last":"Cooper"},"age":28}
+	// 1: {"name":{"first":"Tom","last":"Johnson"},"age":38}
+	// 6: {"name":{"first":"Melinda","last":"Prichard"},"age":44}
+	// 2: {"name":{"first":"Janet","last":"Prichard"},"age":47}
+```
+
 
 ## Data Expiration
 Items can be automatically evicted by using the `SetOptions` object in the `Set` function to set a `TTL`.

buntdb.go

@@ -89,7 +89,7 @@ const (
 	// This is the recommended setting.
 	EverySecond = 1
 	// Always is used to sync data after every write to disk.
-	// Very very slow. Very safe.
+	// Slow. Very safe.
 	Always = 2
 )
 
@@ -202,7 +202,7 @@ type index struct {
 // There are some default less function that can be used such as
 // IndexString, IndexBinary, etc.
 func (db *DB) CreateIndex(name, pattern string,
-	less func(a, b string) bool) error {
+	less ...func(a, b string) bool) error {
 	return db.createIndex(name, pattern, less, nil)
 }
 
@@ -229,7 +229,7 @@ func (db *DB) CreateSpatialIndex(name, pattern string,
 func (db *DB) createIndex(
 	name string,
 	pattern string,
-	less func(a, b string) bool,
+	lessers []func(a, b string) bool,
 	rect func(item string) (min, max []float64),
 ) error {
 	db.mu.Lock()
@@ -243,6 +243,25 @@ func (db *DB) createIndex(
 	if _, ok := db.idxs[name]; ok {
 		return ErrIndexExists
 	}
+	var less func(a, b string) bool
+	switch len(lessers) {
+	default:
+		less = func(a, b string) bool {
+			for i := 0; i < len(lessers)-1; i++ {
+				if lessers[i](a, b) {
+					return true
+				}
+				if lessers[i](b, a) {
+					return false
+				}
+			}
+			return lessers[len(lessers)-1](a, b)
+		}
+	case 0:
+		less = func(a, b string) bool { return false }
+	case 1:
+		less = lessers[0]
+	}
 	idx := &index{
 		name:    name,
 		pattern: pattern,

buntdb_test.go

@@ -414,6 +414,138 @@ func TestVariousTx(t *testing.T) {
 		t.Fatalf("should not be able to perform transactionso on a closed database.")
 	}
 }
+func ExampleDB_CreateIndex_jSON() {
+	db, _ := Open(":memory:")
+	db.CreateIndex("last_name", "*", IndexJSON("name.last"))
+	db.CreateIndex("age", "*", IndexJSON("age"))
+	db.Update(func(tx *Tx) error {
+		tx.Set("1", `{"name":{"first":"Tom","last":"Johnson"},"age":38}`, nil)
+		tx.Set("2", `{"name":{"first":"Janet","last":"Prichard"},"age":47}`, nil)
+		tx.Set("3", `{"name":{"first":"Carol","last":"Anderson"},"age":52}`, nil)
+		tx.Set("4", `{"name":{"first":"Alan","last":"Cooper"},"age":28}`, nil)
+		return nil
+	})
+	db.View(func(tx *Tx) error {
+		fmt.Println("Order by last name")
+		tx.Ascend("last_name", func(key, value string) bool {
+			fmt.Printf("%s: %s\n", key, value)
+			return true
+		})
+		fmt.Println("Order by age")
+		tx.Ascend("age", func(key, value string) bool {
+			fmt.Printf("%s: %s\n", key, value)
+			return true
+		})
+		fmt.Println("Order by age range 30-50")
+		tx.AscendRange("age", `{"age":30}`, `{"age":50}`, func(key, value string) bool {
+			fmt.Printf("%s: %s\n", key, value)
+			return true
+		})
+		return nil
+	})
+
+	// Output:
+	// Order by last name
+	// 3: {"name":{"first":"Carol","last":"Anderson"},"age":52}
+	// 4: {"name":{"first":"Alan","last":"Cooper"},"age":28}
+	// 1: {"name":{"first":"Tom","last":"Johnson"},"age":38}
+	// 2: {"name":{"first":"Janet","last":"Prichard"},"age":47}
+	// Order by age
+	// 4: {"name":{"first":"Alan","last":"Cooper"},"age":28}
+	// 1: {"name":{"first":"Tom","last":"Johnson"},"age":38}
+	// 2: {"name":{"first":"Janet","last":"Prichard"},"age":47}
+	// 3: {"name":{"first":"Carol","last":"Anderson"},"age":52}
+	// Order by age range 30-50
+	// 1: {"name":{"first":"Tom","last":"Johnson"},"age":38}
+	// 2: {"name":{"first":"Janet","last":"Prichard"},"age":47}
+}
+
+func ExampleDB_CreateIndex_strings() {
+	db, _ := Open(":memory:")
+	db.CreateIndex("name", "*", IndexString)
+	db.Update(func(tx *Tx) error {
+		tx.Set("1", "Tom", nil)
+		tx.Set("2", "Janet", nil)
+		tx.Set("3", "Carol", nil)
+		tx.Set("4", "Alan", nil)
+		tx.Set("5", "Sam", nil)
+		tx.Set("6", "Melinda", nil)
+		return nil
+	})
+	db.View(func(tx *Tx) error {
+		tx.Ascend("name", func(key, value string) bool {
+			fmt.Printf("%s: %s\n", key, value)
+			return true
+		})
+		return nil
+	})
+
+	// Output:
+	//4: Alan
+	//3: Carol
+	//2: Janet
+	//6: Melinda
+	//5: Sam
+	//1: Tom
+}
+
+func ExampleDB_CreateIndex_ints() {
+	db, _ := Open(":memory:")
+	db.CreateIndex("age", "*", IndexInt)
+	db.Update(func(tx *Tx) error {
+		tx.Set("1", "30", nil)
+		tx.Set("2", "51", nil)
+		tx.Set("3", "16", nil)
+		tx.Set("4", "76", nil)
+		tx.Set("5", "23", nil)
+		tx.Set("6", "43", nil)
+		return nil
+	})
+	db.View(func(tx *Tx) error {
+		tx.Ascend("age", func(key, value string) bool {
+			fmt.Printf("%s: %s\n", key, value)
+			return true
+		})
+		return nil
+	})
+
+	// Output:
+	//3: 16
+	//5: 23
+	//1: 30
+	//6: 43
+	//2: 51
+	//4: 76
+}
+func ExampleDB_CreateIndex_multipleFields() {
+	db, _ := Open(":memory:")
+	db.CreateIndex("last_name_age", "*", IndexJSON("name.last"), IndexJSON("age"))
+	db.Update(func(tx *Tx) error {
+		tx.Set("1", `{"name":{"first":"Tom","last":"Johnson"},"age":38}`, nil)
+		tx.Set("2", `{"name":{"first":"Janet","last":"Prichard"},"age":47}`, nil)
+		tx.Set("3", `{"name":{"first":"Carol","last":"Anderson"},"age":52}`, nil)
+		tx.Set("4", `{"name":{"first":"Alan","last":"Cooper"},"age":28}`, nil)
+		tx.Set("5", `{"name":{"first":"Sam","last":"Anderson"},"age":51}`, nil)
+		tx.Set("6", `{"name":{"first":"Melinda","last":"Prichard"},"age":44}`, nil)
+		return nil
+	})
+	db.View(func(tx *Tx) error {
+		tx.Ascend("last_name_age", func(key, value string) bool {
+			fmt.Printf("%s: %s\n", key, value)
+			return true
+		})
+		return nil
+	})
+
+	// Output:
+	//5: {"name":{"first":"Sam","last":"Anderson"},"age":51}
+	//3: {"name":{"first":"Carol","last":"Anderson"},"age":52}
+	//4: {"name":{"first":"Alan","last":"Cooper"},"age":28}
+	//1: {"name":{"first":"Tom","last":"Johnson"},"age":38}
+	//6: {"name":{"first":"Melinda","last":"Prichard"},"age":44}
+	//2: {"name":{"first":"Janet","last":"Prichard"},"age":47}
+}
+
 func TestNoExpiringItem(t *testing.T) {
 	item := &dbItem{key: "key", val: "val"}
 	if !item.expiresAt().Equal(maxTime) {