cursor_test.go - external/github.com/boltdb/bolt - Git at Google

 package bolt_test

 import (
 	"bytes"
 	"encoding/binary"
 	"fmt"
 	"os"
 	"sort"
 	"testing"
 	"testing/quick"

 	"github.com/boltdb/bolt"
 )

 // Ensure that a cursor can return a reference to the bucket that created it.
 func TestCursor_Bucket(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()
 	db.Update(func(tx *bolt.Tx) error {
 		b, _ := tx.CreateBucket([]byte("widgets"))
 		c := b.Cursor()
 		equals(t, b, c.Bucket())
 		return nil
 	})
 }

 // Ensure that a Tx cursor can seek to the appropriate keys.
 func TestCursor_Seek(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()
 	db.Update(func(tx *bolt.Tx) error {
 		b, err := tx.CreateBucket([]byte("widgets"))
 		ok(t, err)
 		ok(t, b.Put([]byte("foo"), []byte("0001")))
 		ok(t, b.Put([]byte("bar"), []byte("0002")))
 		ok(t, b.Put([]byte("baz"), []byte("0003")))
 		_, err = b.CreateBucket([]byte("bkt"))
 		ok(t, err)
 		return nil
 	})
 	db.View(func(tx *bolt.Tx) error {
 		c := tx.Bucket([]byte("widgets")).Cursor()

 		// Exact match should go to the key.
 		k, v := c.Seek([]byte("bar"))
 		equals(t, []byte("bar"), k)
 		equals(t, []byte("0002"), v)

 		// Inexact match should go to the next key.
 		k, v = c.Seek([]byte("bas"))
 		equals(t, []byte("baz"), k)
 		equals(t, []byte("0003"), v)

 		// Low key should go to the first key.
 		k, v = c.Seek([]byte(""))
 		equals(t, []byte("bar"), k)
 		equals(t, []byte("0002"), v)

 		// High key should return no key.
 		k, v = c.Seek([]byte("zzz"))
 		assert(t, k == nil, "")
 		assert(t, v == nil, "")

 		// Buckets should return their key but no value.
 		k, v = c.Seek([]byte("bkt"))
 		equals(t, []byte("bkt"), k)
 		assert(t, v == nil, "")

 		return nil
 	})
 }

 func TestCursor_Delete(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	var count = 1000

 	// Insert every other key between 0 and $count.
 	db.Update(func(tx *bolt.Tx) error {
 		b, _ := tx.CreateBucket([]byte("widgets"))
 		for i := 0; i < count; i += 1 {
 			k := make([]byte, 8)
 			binary.BigEndian.PutUint64(k, uint64(i))
 			b.Put(k, make([]byte, 100))
 		}
 		b.CreateBucket([]byte("sub"))
 		return nil
 	})

 	db.Update(func(tx *bolt.Tx) error {
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		bound := make([]byte, 8)
 		binary.BigEndian.PutUint64(bound, uint64(count/2))
 		for key, _ := c.First(); bytes.Compare(key, bound) < 0; key, _ = c.Next() {
 			if err := c.Delete(); err != nil {
 				return err
 			}
 		}
 		c.Seek([]byte("sub"))
 		err := c.Delete()
 		equals(t, err, bolt.ErrIncompatibleValue)
 		return nil
 	})

 	db.View(func(tx *bolt.Tx) error {
 		b := tx.Bucket([]byte("widgets"))
 		equals(t, b.Stats().KeyN, count/2+1)
 		return nil
 	})
 }

 // Ensure that a Tx cursor can seek to the appropriate keys when there are a
 // large number of keys. This test also checks that seek will always move
 // forward to the next key.
 //
 // Related: https://github.com/boltdb/bolt/pull/187
 func TestCursor_Seek_Large(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	var count = 10000

 	// Insert every other key between 0 and $count.
 	db.Update(func(tx *bolt.Tx) error {
 		b, _ := tx.CreateBucket([]byte("widgets"))
 		for i := 0; i < count; i += 100 {
 			for j := i; j < i+100; j += 2 {
 				k := make([]byte, 8)
 				binary.BigEndian.PutUint64(k, uint64(j))
 				b.Put(k, make([]byte, 100))
 			}
 		}
 		return nil
 	})

 	db.View(func(tx *bolt.Tx) error {
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		for i := 0; i < count; i++ {
 			seek := make([]byte, 8)
 			binary.BigEndian.PutUint64(seek, uint64(i))

 			k, _ := c.Seek(seek)

 			// The last seek is beyond the end of the the range so
 			// it should return nil.
 			if i == count-1 {
 				assert(t, k == nil, "")
 				continue
 			}

 			// Otherwise we should seek to the exact key or the next key.
 			num := binary.BigEndian.Uint64(k)
 			if i%2 == 0 {
 				equals(t, uint64(i), num)
 			} else {
 				equals(t, uint64(i+1), num)
 			}
 		}

 		return nil
 	})
 }

 // Ensure that a cursor can iterate over an empty bucket without error.
 func TestCursor_EmptyBucket(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()
 	db.Update(func(tx *bolt.Tx) error {
 		_, err := tx.CreateBucket([]byte("widgets"))
 		return err
 	})
 	db.View(func(tx *bolt.Tx) error {
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		k, v := c.First()
 		assert(t, k == nil, "")
 		assert(t, v == nil, "")
 		return nil
 	})
 }

 // Ensure that a Tx cursor can reverse iterate over an empty bucket without error.
 func TestCursor_EmptyBucketReverse(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	db.Update(func(tx *bolt.Tx) error {
 		_, err := tx.CreateBucket([]byte("widgets"))
 		return err
 	})
 	db.View(func(tx *bolt.Tx) error {
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		k, v := c.Last()
 		assert(t, k == nil, "")
 		assert(t, v == nil, "")
 		return nil
 	})
 }

 // Ensure that a Tx cursor can iterate over a single root with a couple elements.
 func TestCursor_Iterate_Leaf(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	db.Update(func(tx *bolt.Tx) error {
 		tx.CreateBucket([]byte("widgets"))
 		tx.Bucket([]byte("widgets")).Put([]byte("baz"), []byte{})
 		tx.Bucket([]byte("widgets")).Put([]byte("foo"), []byte{0})
 		tx.Bucket([]byte("widgets")).Put([]byte("bar"), []byte{1})
 		return nil
 	})
 	tx, _ := db.Begin(false)
 	c := tx.Bucket([]byte("widgets")).Cursor()

 	k, v := c.First()
 	equals(t, string(k), "bar")
 	equals(t, v, []byte{1})

 	k, v = c.Next()
 	equals(t, string(k), "baz")
 	equals(t, v, []byte{})

 	k, v = c.Next()
 	equals(t, string(k), "foo")
 	equals(t, v, []byte{0})

 	k, v = c.Next()
 	assert(t, k == nil, "")
 	assert(t, v == nil, "")

 	k, v = c.Next()
 	assert(t, k == nil, "")
 	assert(t, v == nil, "")

 	tx.Rollback()
 }

 // Ensure that a Tx cursor can iterate in reverse over a single root with a couple elements.
 func TestCursor_LeafRootReverse(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	db.Update(func(tx *bolt.Tx) error {
 		tx.CreateBucket([]byte("widgets"))
 		tx.Bucket([]byte("widgets")).Put([]byte("baz"), []byte{})
 		tx.Bucket([]byte("widgets")).Put([]byte("foo"), []byte{0})
 		tx.Bucket([]byte("widgets")).Put([]byte("bar"), []byte{1})
 		return nil
 	})
 	tx, _ := db.Begin(false)
 	c := tx.Bucket([]byte("widgets")).Cursor()

 	k, v := c.Last()
 	equals(t, string(k), "foo")
 	equals(t, v, []byte{0})

 	k, v = c.Prev()
 	equals(t, string(k), "baz")
 	equals(t, v, []byte{})

 	k, v = c.Prev()
 	equals(t, string(k), "bar")
 	equals(t, v, []byte{1})

 	k, v = c.Prev()
 	assert(t, k == nil, "")
 	assert(t, v == nil, "")

 	k, v = c.Prev()
 	assert(t, k == nil, "")
 	assert(t, v == nil, "")

 	tx.Rollback()
 }

 // Ensure that a Tx cursor can restart from the beginning.
 func TestCursor_Restart(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	db.Update(func(tx *bolt.Tx) error {
 		tx.CreateBucket([]byte("widgets"))
 		tx.Bucket([]byte("widgets")).Put([]byte("bar"), []byte{})
 		tx.Bucket([]byte("widgets")).Put([]byte("foo"), []byte{})
 		return nil
 	})

 	tx, _ := db.Begin(false)
 	c := tx.Bucket([]byte("widgets")).Cursor()

 	k, _ := c.First()
 	equals(t, string(k), "bar")

 	k, _ = c.Next()
 	equals(t, string(k), "foo")

 	k, _ = c.First()
 	equals(t, string(k), "bar")

 	k, _ = c.Next()
 	equals(t, string(k), "foo")

 	tx.Rollback()
 }

 // Ensure that a Tx can iterate over all elements in a bucket.
 func TestCursor_QuickCheck(t *testing.T) {
 	f := func(items testdata) bool {
 		db := NewTestDB()
 		defer db.Close()

 		// Bulk insert all values.
 		tx, _ := db.Begin(true)
 		tx.CreateBucket([]byte("widgets"))
 		b := tx.Bucket([]byte("widgets"))
 		for _, item := range items {
 			ok(t, b.Put(item.Key, item.Value))
 		}
 		ok(t, tx.Commit())

 		// Sort test data.
 		sort.Sort(items)

 		// Iterate over all items and check consistency.
 		var index = 0
 		tx, _ = db.Begin(false)
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		for k, v := c.First(); k != nil && index < len(items); k, v = c.Next() {
 			equals(t, k, items[index].Key)
 			equals(t, v, items[index].Value)
 			index++
 		}
 		equals(t, len(items), index)
 		tx.Rollback()

 		return true
 	}
 	if err := quick.Check(f, qconfig()); err != nil {
 		t.Error(err)
 	}
 }

 // Ensure that a transaction can iterate over all elements in a bucket in reverse.
 func TestCursor_QuickCheck_Reverse(t *testing.T) {
 	f := func(items testdata) bool {
 		db := NewTestDB()
 		defer db.Close()

 		// Bulk insert all values.
 		tx, _ := db.Begin(true)
 		tx.CreateBucket([]byte("widgets"))
 		b := tx.Bucket([]byte("widgets"))
 		for _, item := range items {
 			ok(t, b.Put(item.Key, item.Value))
 		}
 		ok(t, tx.Commit())

 		// Sort test data.
 		sort.Sort(revtestdata(items))

 		// Iterate over all items and check consistency.
 		var index = 0
 		tx, _ = db.Begin(false)
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		for k, v := c.Last(); k != nil && index < len(items); k, v = c.Prev() {
 			equals(t, k, items[index].Key)
 			equals(t, v, items[index].Value)
 			index++
 		}
 		equals(t, len(items), index)
 		tx.Rollback()

 		return true
 	}
 	if err := quick.Check(f, qconfig()); err != nil {
 		t.Error(err)
 	}
 }

 // Ensure that a Tx cursor can iterate over subbuckets.
 func TestCursor_QuickCheck_BucketsOnly(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	db.Update(func(tx *bolt.Tx) error {
 		b, err := tx.CreateBucket([]byte("widgets"))
 		ok(t, err)
 		_, err = b.CreateBucket([]byte("foo"))
 		ok(t, err)
 		_, err = b.CreateBucket([]byte("bar"))
 		ok(t, err)
 		_, err = b.CreateBucket([]byte("baz"))
 		ok(t, err)
 		return nil
 	})
 	db.View(func(tx *bolt.Tx) error {
 		var names []string
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		for k, v := c.First(); k != nil; k, v = c.Next() {
 			names = append(names, string(k))
 			assert(t, v == nil, "")
 		}
 		equals(t, names, []string{"bar", "baz", "foo"})
 		return nil
 	})
 }

 // Ensure that a Tx cursor can reverse iterate over subbuckets.
 func TestCursor_QuickCheck_BucketsOnly_Reverse(t *testing.T) {
 	db := NewTestDB()
 	defer db.Close()

 	db.Update(func(tx *bolt.Tx) error {
 		b, err := tx.CreateBucket([]byte("widgets"))
 		ok(t, err)
 		_, err = b.CreateBucket([]byte("foo"))
 		ok(t, err)
 		_, err = b.CreateBucket([]byte("bar"))
 		ok(t, err)
 		_, err = b.CreateBucket([]byte("baz"))
 		ok(t, err)
 		return nil
 	})
 	db.View(func(tx *bolt.Tx) error {
 		var names []string
 		c := tx.Bucket([]byte("widgets")).Cursor()
 		for k, v := c.Last(); k != nil; k, v = c.Prev() {
 			names = append(names, string(k))
 			assert(t, v == nil, "")
 		}
 		equals(t, names, []string{"foo", "baz", "bar"})
 		return nil
 	})
 }

 func ExampleCursor() {
 	// Open the database.
 	db, _ := bolt.Open(tempfile(), 0666, nil)
 	defer os.Remove(db.Path())
 	defer db.Close()

 	// Start a read-write transaction.
 	db.Update(func(tx *bolt.Tx) error {
 		// Create a new bucket.
 		tx.CreateBucket([]byte("animals"))

 		// Insert data into a bucket.
 		b := tx.Bucket([]byte("animals"))
 		b.Put([]byte("dog"), []byte("fun"))
 		b.Put([]byte("cat"), []byte("lame"))
 		b.Put([]byte("liger"), []byte("awesome"))

 		// Create a cursor for iteration.
 		c := b.Cursor()

 		// Iterate over items in sorted key order. This starts from the
 		// first key/value pair and updates the k/v variables to the
 		// next key/value on each iteration.
 		//
 		// The loop finishes at the end of the cursor when a nil key is returned.
 		for k, v := c.First(); k != nil; k, v = c.Next() {
 			fmt.Printf("A %s is %s.\n", k, v)
 		}

 		return nil
 	})

 	// Output:
 	// A cat is lame.
 	// A dog is fun.
 	// A liger is awesome.
 }

 func ExampleCursor_reverse() {
 	// Open the database.
 	db, _ := bolt.Open(tempfile(), 0666, nil)
 	defer os.Remove(db.Path())
 	defer db.Close()

 	// Start a read-write transaction.
 	db.Update(func(tx *bolt.Tx) error {
 		// Create a new bucket.
 		tx.CreateBucket([]byte("animals"))

 		// Insert data into a bucket.
 		b := tx.Bucket([]byte("animals"))
 		b.Put([]byte("dog"), []byte("fun"))
 		b.Put([]byte("cat"), []byte("lame"))
 		b.Put([]byte("liger"), []byte("awesome"))

 		// Create a cursor for iteration.
 		c := b.Cursor()

 		// Iterate over items in reverse sorted key order. This starts
 		// from the last key/value pair and updates the k/v variables to
 		// the previous key/value on each iteration.
 		//
 		// The loop finishes at the beginning of the cursor when a nil key
 		// is returned.
 		for k, v := c.Last(); k != nil; k, v = c.Prev() {
 			fmt.Printf("A %s is %s.\n", k, v)
 		}

 		return nil
 	})

 	// Output:
 	// A liger is awesome.
 	// A dog is fun.
 	// A cat is lame.
 }
	package bolt_test

	import (
	"bytes"
	"encoding/binary"
	"fmt"
	"os"
	"sort"
	"testing"
	"testing/quick"

	"github.com/boltdb/bolt"
	)

	// Ensure that a cursor can return a reference to the bucket that created it.
	func TestCursor_Bucket(t *testing.T) {
	db := NewTestDB()
	defer db.Close()
	db.Update(func(tx *bolt.Tx) error {
	b, _ := tx.CreateBucket([]byte("widgets"))
	c := b.Cursor()
	equals(t, b, c.Bucket())
	return nil
	})
	}

	// Ensure that a Tx cursor can seek to the appropriate keys.
	func TestCursor_Seek(t *testing.T) {
	db := NewTestDB()
	defer db.Close()
	db.Update(func(tx *bolt.Tx) error {
	b, err := tx.CreateBucket([]byte("widgets"))
	ok(t, err)
	ok(t, b.Put([]byte("foo"), []byte("0001")))
	ok(t, b.Put([]byte("bar"), []byte("0002")))
	ok(t, b.Put([]byte("baz"), []byte("0003")))
	_, err = b.CreateBucket([]byte("bkt"))
	ok(t, err)
	return nil
	})
	db.View(func(tx *bolt.Tx) error {
	c := tx.Bucket([]byte("widgets")).Cursor()

	// Exact match should go to the key.
	k, v := c.Seek([]byte("bar"))
	equals(t, []byte("bar"), k)
	equals(t, []byte("0002"), v)

	// Inexact match should go to the next key.
	k, v = c.Seek([]byte("bas"))
	equals(t, []byte("baz"), k)
	equals(t, []byte("0003"), v)

	// Low key should go to the first key.
	k, v = c.Seek([]byte(""))
	equals(t, []byte("bar"), k)
	equals(t, []byte("0002"), v)

	// High key should return no key.
	k, v = c.Seek([]byte("zzz"))
	assert(t, k == nil, "")
	assert(t, v == nil, "")

	// Buckets should return their key but no value.
	k, v = c.Seek([]byte("bkt"))
	equals(t, []byte("bkt"), k)
	assert(t, v == nil, "")

	return nil
	})
	}

	func TestCursor_Delete(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	var count = 1000

	// Insert every other key between 0 and $count.
	db.Update(func(tx *bolt.Tx) error {
	b, _ := tx.CreateBucket([]byte("widgets"))
	for i := 0; i < count; i += 1 {
	k := make([]byte, 8)
	binary.BigEndian.PutUint64(k, uint64(i))
	b.Put(k, make([]byte, 100))
	}
	b.CreateBucket([]byte("sub"))
	return nil
	})

	db.Update(func(tx *bolt.Tx) error {
	c := tx.Bucket([]byte("widgets")).Cursor()
	bound := make([]byte, 8)
	binary.BigEndian.PutUint64(bound, uint64(count/2))
	for key, _ := c.First(); bytes.Compare(key, bound) < 0; key, _ = c.Next() {
	if err := c.Delete(); err != nil {
	return err
	}
	}
	c.Seek([]byte("sub"))
	err := c.Delete()
	equals(t, err, bolt.ErrIncompatibleValue)
	return nil
	})

	db.View(func(tx *bolt.Tx) error {
	b := tx.Bucket([]byte("widgets"))
	equals(t, b.Stats().KeyN, count/2+1)
	return nil
	})
	}

	// Ensure that a Tx cursor can seek to the appropriate keys when there are a
	// large number of keys. This test also checks that seek will always move
	// forward to the next key.
	//
	// Related: https://github.com/boltdb/bolt/pull/187
	func TestCursor_Seek_Large(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	var count = 10000

	// Insert every other key between 0 and $count.
	db.Update(func(tx *bolt.Tx) error {
	b, _ := tx.CreateBucket([]byte("widgets"))
	for i := 0; i < count; i += 100 {
	for j := i; j < i+100; j += 2 {
	k := make([]byte, 8)
	binary.BigEndian.PutUint64(k, uint64(j))
	b.Put(k, make([]byte, 100))
	}
	}
	return nil
	})

	db.View(func(tx *bolt.Tx) error {
	c := tx.Bucket([]byte("widgets")).Cursor()
	for i := 0; i < count; i++ {
	seek := make([]byte, 8)
	binary.BigEndian.PutUint64(seek, uint64(i))

	k, _ := c.Seek(seek)

	// The last seek is beyond the end of the the range so
	// it should return nil.
	if i == count-1 {
	assert(t, k == nil, "")
	continue
	}

	// Otherwise we should seek to the exact key or the next key.
	num := binary.BigEndian.Uint64(k)
	if i%2 == 0 {
	equals(t, uint64(i), num)
	} else {
	equals(t, uint64(i+1), num)
	}
	}

	return nil
	})
	}

	// Ensure that a cursor can iterate over an empty bucket without error.
	func TestCursor_EmptyBucket(t *testing.T) {
	db := NewTestDB()
	defer db.Close()
	db.Update(func(tx *bolt.Tx) error {
	_, err := tx.CreateBucket([]byte("widgets"))
	return err
	})
	db.View(func(tx *bolt.Tx) error {
	c := tx.Bucket([]byte("widgets")).Cursor()
	k, v := c.First()
	assert(t, k == nil, "")
	assert(t, v == nil, "")
	return nil
	})
	}

	// Ensure that a Tx cursor can reverse iterate over an empty bucket without error.
	func TestCursor_EmptyBucketReverse(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	db.Update(func(tx *bolt.Tx) error {
	_, err := tx.CreateBucket([]byte("widgets"))
	return err
	})
	db.View(func(tx *bolt.Tx) error {
	c := tx.Bucket([]byte("widgets")).Cursor()
	k, v := c.Last()
	assert(t, k == nil, "")
	assert(t, v == nil, "")
	return nil
	})
	}

	// Ensure that a Tx cursor can iterate over a single root with a couple elements.
	func TestCursor_Iterate_Leaf(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	db.Update(func(tx *bolt.Tx) error {
	tx.CreateBucket([]byte("widgets"))
	tx.Bucket([]byte("widgets")).Put([]byte("baz"), []byte{})
	tx.Bucket([]byte("widgets")).Put([]byte("foo"), []byte{0})
	tx.Bucket([]byte("widgets")).Put([]byte("bar"), []byte{1})
	return nil
	})
	tx, _ := db.Begin(false)
	c := tx.Bucket([]byte("widgets")).Cursor()

	k, v := c.First()
	equals(t, string(k), "bar")
	equals(t, v, []byte{1})

	k, v = c.Next()
	equals(t, string(k), "baz")
	equals(t, v, []byte{})

	k, v = c.Next()
	equals(t, string(k), "foo")
	equals(t, v, []byte{0})

	k, v = c.Next()
	assert(t, k == nil, "")
	assert(t, v == nil, "")

	k, v = c.Next()
	assert(t, k == nil, "")
	assert(t, v == nil, "")

	tx.Rollback()
	}

	// Ensure that a Tx cursor can iterate in reverse over a single root with a couple elements.
	func TestCursor_LeafRootReverse(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	db.Update(func(tx *bolt.Tx) error {
	tx.CreateBucket([]byte("widgets"))
	tx.Bucket([]byte("widgets")).Put([]byte("baz"), []byte{})
	tx.Bucket([]byte("widgets")).Put([]byte("foo"), []byte{0})
	tx.Bucket([]byte("widgets")).Put([]byte("bar"), []byte{1})
	return nil
	})
	tx, _ := db.Begin(false)
	c := tx.Bucket([]byte("widgets")).Cursor()

	k, v := c.Last()
	equals(t, string(k), "foo")
	equals(t, v, []byte{0})

	k, v = c.Prev()
	equals(t, string(k), "baz")
	equals(t, v, []byte{})

	k, v = c.Prev()
	equals(t, string(k), "bar")
	equals(t, v, []byte{1})

	k, v = c.Prev()
	assert(t, k == nil, "")
	assert(t, v == nil, "")

	k, v = c.Prev()
	assert(t, k == nil, "")
	assert(t, v == nil, "")

	tx.Rollback()
	}

	// Ensure that a Tx cursor can restart from the beginning.
	func TestCursor_Restart(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	db.Update(func(tx *bolt.Tx) error {
	tx.CreateBucket([]byte("widgets"))
	tx.Bucket([]byte("widgets")).Put([]byte("bar"), []byte{})
	tx.Bucket([]byte("widgets")).Put([]byte("foo"), []byte{})
	return nil
	})

	tx, _ := db.Begin(false)
	c := tx.Bucket([]byte("widgets")).Cursor()

	k, _ := c.First()
	equals(t, string(k), "bar")

	k, _ = c.Next()
	equals(t, string(k), "foo")

	k, _ = c.First()
	equals(t, string(k), "bar")

	k, _ = c.Next()
	equals(t, string(k), "foo")

	tx.Rollback()
	}

	// Ensure that a Tx can iterate over all elements in a bucket.
	func TestCursor_QuickCheck(t *testing.T) {
	f := func(items testdata) bool {
	db := NewTestDB()
	defer db.Close()

	// Bulk insert all values.
	tx, _ := db.Begin(true)
	tx.CreateBucket([]byte("widgets"))
	b := tx.Bucket([]byte("widgets"))
	for _, item := range items {
	ok(t, b.Put(item.Key, item.Value))
	}
	ok(t, tx.Commit())

	// Sort test data.
	sort.Sort(items)

	// Iterate over all items and check consistency.
	var index = 0
	tx, _ = db.Begin(false)
	c := tx.Bucket([]byte("widgets")).Cursor()
	for k, v := c.First(); k != nil && index < len(items); k, v = c.Next() {
	equals(t, k, items[index].Key)
	equals(t, v, items[index].Value)
	index++
	}
	equals(t, len(items), index)
	tx.Rollback()

	return true
	}
	if err := quick.Check(f, qconfig()); err != nil {
	t.Error(err)
	}
	}

	// Ensure that a transaction can iterate over all elements in a bucket in reverse.
	func TestCursor_QuickCheck_Reverse(t *testing.T) {
	f := func(items testdata) bool {
	db := NewTestDB()
	defer db.Close()

	// Bulk insert all values.
	tx, _ := db.Begin(true)
	tx.CreateBucket([]byte("widgets"))
	b := tx.Bucket([]byte("widgets"))
	for _, item := range items {
	ok(t, b.Put(item.Key, item.Value))
	}
	ok(t, tx.Commit())

	// Sort test data.
	sort.Sort(revtestdata(items))

	// Iterate over all items and check consistency.
	var index = 0
	tx, _ = db.Begin(false)
	c := tx.Bucket([]byte("widgets")).Cursor()
	for k, v := c.Last(); k != nil && index < len(items); k, v = c.Prev() {
	equals(t, k, items[index].Key)
	equals(t, v, items[index].Value)
	index++
	}
	equals(t, len(items), index)
	tx.Rollback()

	return true
	}
	if err := quick.Check(f, qconfig()); err != nil {
	t.Error(err)
	}
	}

	// Ensure that a Tx cursor can iterate over subbuckets.
	func TestCursor_QuickCheck_BucketsOnly(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	db.Update(func(tx *bolt.Tx) error {
	b, err := tx.CreateBucket([]byte("widgets"))
	ok(t, err)
	_, err = b.CreateBucket([]byte("foo"))
	ok(t, err)
	_, err = b.CreateBucket([]byte("bar"))
	ok(t, err)
	_, err = b.CreateBucket([]byte("baz"))
	ok(t, err)
	return nil
	})
	db.View(func(tx *bolt.Tx) error {
	var names []string
	c := tx.Bucket([]byte("widgets")).Cursor()
	for k, v := c.First(); k != nil; k, v = c.Next() {
	names = append(names, string(k))
	assert(t, v == nil, "")
	}
	equals(t, names, []string{"bar", "baz", "foo"})
	return nil
	})
	}

	// Ensure that a Tx cursor can reverse iterate over subbuckets.
	func TestCursor_QuickCheck_BucketsOnly_Reverse(t *testing.T) {
	db := NewTestDB()
	defer db.Close()

	db.Update(func(tx *bolt.Tx) error {
	b, err := tx.CreateBucket([]byte("widgets"))
	ok(t, err)
	_, err = b.CreateBucket([]byte("foo"))
	ok(t, err)
	_, err = b.CreateBucket([]byte("bar"))
	ok(t, err)
	_, err = b.CreateBucket([]byte("baz"))
	ok(t, err)
	return nil
	})
	db.View(func(tx *bolt.Tx) error {
	var names []string
	c := tx.Bucket([]byte("widgets")).Cursor()
	for k, v := c.Last(); k != nil; k, v = c.Prev() {
	names = append(names, string(k))
	assert(t, v == nil, "")
	}
	equals(t, names, []string{"foo", "baz", "bar"})
	return nil
	})
	}

	func ExampleCursor() {
	// Open the database.
	db, _ := bolt.Open(tempfile(), 0666, nil)
	defer os.Remove(db.Path())
	defer db.Close()

	// Start a read-write transaction.
	db.Update(func(tx *bolt.Tx) error {
	// Create a new bucket.
	tx.CreateBucket([]byte("animals"))

	// Insert data into a bucket.
	b := tx.Bucket([]byte("animals"))
	b.Put([]byte("dog"), []byte("fun"))
	b.Put([]byte("cat"), []byte("lame"))
	b.Put([]byte("liger"), []byte("awesome"))

	// Create a cursor for iteration.
	c := b.Cursor()

	// Iterate over items in sorted key order. This starts from the
	// first key/value pair and updates the k/v variables to the
	// next key/value on each iteration.
	//
	// The loop finishes at the end of the cursor when a nil key is returned.
	for k, v := c.First(); k != nil; k, v = c.Next() {
	fmt.Printf("A %s is %s.\n", k, v)
	}

	return nil
	})

	// Output:
	// A cat is lame.
	// A dog is fun.
	// A liger is awesome.
	}

	func ExampleCursor_reverse() {
	// Open the database.
	db, _ := bolt.Open(tempfile(), 0666, nil)
	defer os.Remove(db.Path())
	defer db.Close()

	// Start a read-write transaction.
	db.Update(func(tx *bolt.Tx) error {
	// Create a new bucket.
	tx.CreateBucket([]byte("animals"))

	// Insert data into a bucket.
	b := tx.Bucket([]byte("animals"))
	b.Put([]byte("dog"), []byte("fun"))
	b.Put([]byte("cat"), []byte("lame"))
	b.Put([]byte("liger"), []byte("awesome"))

	// Create a cursor for iteration.
	c := b.Cursor()

	// Iterate over items in reverse sorted key order. This starts
	// from the last key/value pair and updates the k/v variables to
	// the previous key/value on each iteration.
	//
	// The loop finishes at the beginning of the cursor when a nil key
	// is returned.
	for k, v := c.Last(); k != nil; k, v = c.Prev() {
	fmt.Printf("A %s is %s.\n", k, v)
	}

	return nil
	})

	// Output:
	// A liger is awesome.
	// A dog is fun.
	// A cat is lame.
	}