func scopedUpdate(ns walletdb.Namespace, f func(walletdb.Bucket) error) error {
	tx, err := ns.Begin(true)
	if err != nil {
		str := "cannot begin update"
		return storeError(ErrDatabase, str, err)
	}
	err = f(tx.RootBucket())
	if err != nil {
		rbErr := tx.Rollback()
		if rbErr != nil {
			const desc = "rollback failed"
			serr, ok := err.(Error)
			if !ok {
				// This really shouldn't happen.
				return storeError(ErrDatabase, desc, rbErr)
			}
			serr.Desc = desc + ": " + serr.Desc
			return serr
		}
		return err
	}
	err = tx.Commit()
	if err != nil {
		str := "commit failed"
		return storeError(ErrDatabase, str, err)
	}
	return nil
}

// Create creates a new entry in the database with the given ID
// and returns the Pool representing it.
func Create(namespace walletdb.Namespace, m *waddrmgr.Manager, poolID []byte) (*Pool, error) {
	err := namespace.Update(
		func(tx walletdb.Tx) error {
			return putPool(tx, poolID)
		})
	if err != nil {
		str := fmt.Sprintf("unable to add voting pool %v to db", poolID)
		return nil, newError(ErrPoolAlreadyExists, str, err)
	}
	return newPool(namespace, m, poolID), nil
}

func scopedView(ns walletdb.Namespace, f func(walletdb.Bucket) error) error {
	tx, err := ns.Begin(false)
	if err != nil {
		str := "cannot begin view"
		return storeError(ErrDatabase, str, err)
	}
	err = f(tx.RootBucket())
	rbErr := tx.Rollback()
	if err != nil {
		return err
	}
	if rbErr != nil {
		str := "cannot close view"
		return storeError(ErrDatabase, str, rbErr)
	}
	return nil
}

// Load fetches the entry in the database with the given ID and returns the Pool
// representing it.
func Load(namespace walletdb.Namespace, m *waddrmgr.Manager, poolID []byte) (*Pool, error) {
	err := namespace.View(
		func(tx walletdb.Tx) error {
			if exists := existsPool(tx, poolID); !exists {
				str := fmt.Sprintf("unable to find voting pool %v in db", poolID)
				return newError(ErrPoolNotExists, str, nil)
			}
			return nil
		})
	if err != nil {
		return nil, err
	}
	p := newPool(namespace, m, poolID)
	if err = p.LoadAllSeries(); err != nil {
		return nil, err
	}
	return p, nil
}

// testManualTxInterface ensures that manual transactions work as expected.
func testManualTxInterface(tc *testContext, namespace walletdb.Namespace) bool {
	// populateValues tests that populating values works as expected.
	//
	// When the writable flag is false, a read-only tranasction is created,
	// standard bucket tests for read-only transactions are performed, and
	// the Commit function is checked to ensure it fails as expected.
	//
	// Otherwise, a read-write transaction is created, the values are
	// written, standard bucket tests for read-write transactions are
	// performed, and then the transaction is either commited or rolled
	// back depending on the flag.
	populateValues := func(writable, rollback bool, putValues map[string]string) bool {
		tx, err := namespace.Begin(writable)
		if err != nil {
			tc.t.Errorf("Begin: unexpected error %v", err)
			return false
		}

		rootBucket := tx.RootBucket()
		if rootBucket == nil {
			tc.t.Errorf("RootBucket: unexpected nil root bucket")
			_ = tx.Rollback()
			return false
		}

		tc.isWritable = writable
		if !testBucketInterface(tc, rootBucket) {
			_ = tx.Rollback()
			return false
		}

		if !writable {
			// The transaction is not writable, so it should fail
			// the commit.
			if err := tx.Commit(); err != walletdb.ErrTxNotWritable {
				tc.t.Errorf("Commit: unexpected error %v, "+
					"want %v", err, walletdb.ErrTxNotWritable)
				_ = tx.Rollback()
				return false
			}

			// Rollback the transaction.
			if err := tx.Rollback(); err != nil {
				tc.t.Errorf("Commit: unexpected error %v", err)
				return false
			}
		} else {
			if !testPutValues(tc, rootBucket, putValues) {
				return false
			}

			if rollback {
				// Rollback the transaction.
				if err := tx.Rollback(); err != nil {
					tc.t.Errorf("Rollback: unexpected "+
						"error %v", err)
					return false
				}
			} else {
				// The commit should succeed.
				if err := tx.Commit(); err != nil {
					tc.t.Errorf("Commit: unexpected error "+
						"%v", err)
					return false
				}
			}
		}

		return true
	}

	// checkValues starts a read-only transaction and checks that all of
	// the key/value pairs specified in the expectedValues parameter match
	// what's in the database.
	checkValues := func(expectedValues map[string]string) bool {
		// Begin another read-only transaction to ensure...
		tx, err := namespace.Begin(false)
		if err != nil {
			tc.t.Errorf("Begin: unexpected error %v", err)
			return false
		}

		rootBucket := tx.RootBucket()
		if rootBucket == nil {
			tc.t.Errorf("RootBucket: unexpected nil root bucket")
			_ = tx.Rollback()
			return false
		}

		if !testGetValues(tc, rootBucket, expectedValues) {
			_ = tx.Rollback()
			return false
		}

		// Rollback the read-only transaction.
		if err := tx.Rollback(); err != nil {
			tc.t.Errorf("Commit: unexpected error %v", err)
			return false
		}
//.........这里部分代码省略.........