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|
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package sql provides a generic interface around SQL (or SQL-like)
// databases.
package sql
import (
"errors"
"fmt"
"io"
"sync"
"exp/sql/driver"
)
var drivers = make(map[string]driver.Driver)
// Register makes a database driver available by the provided name.
// If Register is called twice with the same name or if driver is nil,
// it panics.
func Register(name string, driver driver.Driver) {
if driver == nil {
panic("sql: Register driver is nil")
}
if _, dup := drivers[name]; dup {
panic("sql: Register called twice for driver " + name)
}
drivers[name] = driver
}
// NullableString represents a string that may be null.
// NullableString implements the ScannerInto interface so
// it can be used as a scan destination:
//
// var s NullableString
// err := db.QueryRow("SELECT name FROM foo WHERE id=?", id).Scan(&s)
// ...
// if s.Valid {
// // use s.String
// } else {
// // NULL value
// }
//
// TODO(bradfitz): add other types.
type NullableString struct {
String string
Valid bool // Valid is true if String is not NULL
}
// ScanInto implements the ScannerInto interface.
func (ms *NullableString) ScanInto(value interface{}) error {
if value == nil {
ms.String, ms.Valid = "", false
return nil
}
ms.Valid = true
return convertAssign(&ms.String, value)
}
// ScannerInto is an interface used by Scan.
type ScannerInto interface {
// ScanInto assigns a value from a database driver.
//
// The value will be of one of the following restricted
// set of types:
//
// int64
// float64
// bool
// []byte
// nil - for NULL values
//
// An error should be returned if the value can not be stored
// without loss of information.
ScanInto(value interface{}) error
}
// ErrNoRows is returned by Scan when QueryRow doesn't return a
// row. In such a case, QueryRow returns a placeholder *Row value that
// defers this error until a Scan.
var ErrNoRows = errors.New("sql: no rows in result set")
// DB is a database handle. It's safe for concurrent use by multiple
// goroutines.
type DB struct {
driver driver.Driver
dsn string
mu sync.Mutex // protects freeConn and closed
freeConn []driver.Conn
closed bool
}
// Open opens a database specified by its database driver name and a
// driver-specific data source name, usually consisting of at least a
// database name and connection information.
//
// Most users will open a database via a driver-specific connection
// helper function that returns a *DB.
func Open(driverName, dataSourceName string) (*DB, error) {
driver, ok := drivers[driverName]
if !ok {
return nil, fmt.Errorf("sql: unknown driver %q (forgotten import?)", driverName)
}
return &DB{driver: driver, dsn: dataSourceName}, nil
}
// Close closes the database, releasing any open resources.
func (db *DB) Close() error {
db.mu.Lock()
defer db.mu.Unlock()
var err error
for _, c := range db.freeConn {
err1 := c.Close()
if err1 != nil {
err = err1
}
}
db.freeConn = nil
db.closed = true
return err
}
func (db *DB) maxIdleConns() int {
const defaultMaxIdleConns = 2
// TODO(bradfitz): ask driver, if supported, for its default preference
// TODO(bradfitz): let users override?
return defaultMaxIdleConns
}
// conn returns a newly-opened or cached driver.Conn
func (db *DB) conn() (driver.Conn, error) {
db.mu.Lock()
if db.closed {
db.mu.Unlock()
return nil, errors.New("sql: database is closed")
}
if n := len(db.freeConn); n > 0 {
conn := db.freeConn[n-1]
db.freeConn = db.freeConn[:n-1]
db.mu.Unlock()
return conn, nil
}
db.mu.Unlock()
return db.driver.Open(db.dsn)
}
func (db *DB) connIfFree(wanted driver.Conn) (conn driver.Conn, ok bool) {
db.mu.Lock()
defer db.mu.Unlock()
for n, conn := range db.freeConn {
if conn == wanted {
db.freeConn[n] = db.freeConn[len(db.freeConn)-1]
db.freeConn = db.freeConn[:len(db.freeConn)-1]
return wanted, true
}
}
return nil, false
}
func (db *DB) putConn(c driver.Conn) {
db.mu.Lock()
defer db.mu.Unlock()
if n := len(db.freeConn); !db.closed && n < db.maxIdleConns() {
db.freeConn = append(db.freeConn, c)
return
}
db.closeConn(c) // TODO(bradfitz): release lock before calling this?
}
func (db *DB) closeConn(c driver.Conn) {
// TODO: check to see if we need this Conn for any prepared statements
// that are active.
c.Close()
}
// Prepare creates a prepared statement for later execution.
func (db *DB) Prepare(query string) (*Stmt, error) {
// TODO: check if db.driver supports an optional
// driver.Preparer interface and call that instead, if so,
// otherwise we make a prepared statement that's bound
// to a connection, and to execute this prepared statement
// we either need to use this connection (if it's free), else
// get a new connection + re-prepare + execute on that one.
ci, err := db.conn()
if err != nil {
return nil, err
}
defer db.putConn(ci)
si, err := ci.Prepare(query)
if err != nil {
return nil, err
}
stmt := &Stmt{
db: db,
query: query,
css: []connStmt{{ci, si}},
}
return stmt, nil
}
// Exec executes a query without returning any rows.
func (db *DB) Exec(query string, args ...interface{}) (Result, error) {
sargs, err := subsetTypeArgs(args)
if err != nil {
return nil, err
}
ci, err := db.conn()
if err != nil {
return nil, err
}
defer db.putConn(ci)
if execer, ok := ci.(driver.Execer); ok {
resi, err := execer.Exec(query, sargs)
if err != driver.ErrSkip {
if err != nil {
return nil, err
}
return result{resi}, nil
}
}
sti, err := ci.Prepare(query)
if err != nil {
return nil, err
}
defer sti.Close()
resi, err := sti.Exec(sargs)
if err != nil {
return nil, err
}
return result{resi}, nil
}
// Query executes a query that returns rows, typically a SELECT.
func (db *DB) Query(query string, args ...interface{}) (*Rows, error) {
stmt, err := db.Prepare(query)
if err != nil {
return nil, err
}
rows, err := stmt.Query(args...)
if err != nil {
stmt.Close()
return nil, err
}
rows.closeStmt = stmt
return rows, nil
}
// QueryRow executes a query that is expected to return at most one row.
// QueryRow always return a non-nil value. Errors are deferred until
// Row's Scan method is called.
func (db *DB) QueryRow(query string, args ...interface{}) *Row {
rows, err := db.Query(query, args...)
return &Row{rows: rows, err: err}
}
// Begin starts a transaction. The isolation level is dependent on
// the driver.
func (db *DB) Begin() (*Tx, error) {
ci, err := db.conn()
if err != nil {
return nil, err
}
txi, err := ci.Begin()
if err != nil {
db.putConn(ci)
return nil, fmt.Errorf("sql: failed to Begin transaction: %v", err)
}
return &Tx{
db: db,
ci: ci,
txi: txi,
}, nil
}
// DriverDatabase returns the database's underlying driver.
func (db *DB) Driver() driver.Driver {
return db.driver
}
// Tx is an in-progress database transaction.
//
// A transaction must end with a call to Commit or Rollback.
//
// After a call to Commit or Rollback, all operations on the
// transaction fail with ErrTransactionFinished.
type Tx struct {
db *DB
// ci is owned exclusively until Commit or Rollback, at which point
// it's returned with putConn.
ci driver.Conn
txi driver.Tx
// cimu is held while somebody is using ci (between grabConn
// and releaseConn)
cimu sync.Mutex
// done transitions from false to true exactly once, on Commit
// or Rollback. once done, all operations fail with
// ErrTransactionFinished.
done bool
}
var ErrTransactionFinished = errors.New("sql: Transaction has already been committed or rolled back")
func (tx *Tx) close() {
if tx.done {
panic("double close") // internal error
}
tx.done = true
tx.db.putConn(tx.ci)
tx.ci = nil
tx.txi = nil
}
func (tx *Tx) grabConn() (driver.Conn, error) {
if tx.done {
return nil, ErrTransactionFinished
}
tx.cimu.Lock()
return tx.ci, nil
}
func (tx *Tx) releaseConn() {
tx.cimu.Unlock()
}
// Commit commits the transaction.
func (tx *Tx) Commit() error {
if tx.done {
return ErrTransactionFinished
}
defer tx.close()
return tx.txi.Commit()
}
// Rollback aborts the transaction.
func (tx *Tx) Rollback() error {
if tx.done {
return ErrTransactionFinished
}
defer tx.close()
return tx.txi.Rollback()
}
// Prepare creates a prepared statement for use within a transaction.
//
// The returned statement operates within the transaction and can no longer
// be used once the transaction has been committed or rolled back.
//
// To use an existing prepared statement on this transaction, see Tx.Stmt.
func (tx *Tx) Prepare(query string) (*Stmt, error) {
// TODO(bradfitz): We could be more efficient here and either
// provide a method to take an existing Stmt (created on
// perhaps a different Conn), and re-create it on this Conn if
// necessary. Or, better: keep a map in DB of query string to
// Stmts, and have Stmt.Execute do the right thing and
// re-prepare if the Conn in use doesn't have that prepared
// statement. But we'll want to avoid caching the statement
// in the case where we only call conn.Prepare implicitly
// (such as in db.Exec or tx.Exec), but the caller package
// can't be holding a reference to the returned statement.
// Perhaps just looking at the reference count (by noting
// Stmt.Close) would be enough. We might also want a finalizer
// on Stmt to drop the reference count.
ci, err := tx.grabConn()
if err != nil {
return nil, err
}
defer tx.releaseConn()
si, err := ci.Prepare(query)
if err != nil {
return nil, err
}
stmt := &Stmt{
db: tx.db,
tx: tx,
txsi: si,
query: query,
}
return stmt, nil
}
// Stmt returns a transaction-specific prepared statement from
// an existing statement.
//
// Example:
// updateMoney, err := db.Prepare("UPDATE balance SET money=money+? WHERE id=?")
// ...
// tx, err := db.Begin()
// ...
// res, err := tx.Stmt(updateMoney).Exec(123.45, 98293203)
func (tx *Tx) Stmt(stmt *Stmt) *Stmt {
// TODO(bradfitz): optimize this. Currently this re-prepares
// each time. This is fine for now to illustrate the API but
// we should really cache already-prepared statements
// per-Conn. See also the big comment in Tx.Prepare.
if tx.db != stmt.db {
return &Stmt{stickyErr: errors.New("sql: Tx.Stmt: statement from different database used")}
}
ci, err := tx.grabConn()
if err != nil {
return &Stmt{stickyErr: err}
}
defer tx.releaseConn()
si, err := ci.Prepare(stmt.query)
return &Stmt{
db: tx.db,
tx: tx,
txsi: si,
query: stmt.query,
stickyErr: err,
}
}
// Exec executes a query that doesn't return rows.
// For example: an INSERT and UPDATE.
func (tx *Tx) Exec(query string, args ...interface{}) (Result, error) {
ci, err := tx.grabConn()
if err != nil {
return nil, err
}
defer tx.releaseConn()
if execer, ok := ci.(driver.Execer); ok {
resi, err := execer.Exec(query, args)
if err != nil {
return nil, err
}
return result{resi}, nil
}
sti, err := ci.Prepare(query)
if err != nil {
return nil, err
}
defer sti.Close()
sargs, err := subsetTypeArgs(args)
if err != nil {
return nil, err
}
resi, err := sti.Exec(sargs)
if err != nil {
return nil, err
}
return result{resi}, nil
}
// Query executes a query that returns rows, typically a SELECT.
func (tx *Tx) Query(query string, args ...interface{}) (*Rows, error) {
if tx.done {
return nil, ErrTransactionFinished
}
stmt, err := tx.Prepare(query)
if err != nil {
return nil, err
}
defer stmt.Close()
return stmt.Query(args...)
}
// QueryRow executes a query that is expected to return at most one row.
// QueryRow always return a non-nil value. Errors are deferred until
// Row's Scan method is called.
func (tx *Tx) QueryRow(query string, args ...interface{}) *Row {
rows, err := tx.Query(query, args...)
return &Row{rows: rows, err: err}
}
// connStmt is a prepared statement on a particular connection.
type connStmt struct {
ci driver.Conn
si driver.Stmt
}
// Stmt is a prepared statement. Stmt is safe for concurrent use by multiple goroutines.
type Stmt struct {
// Immutable:
db *DB // where we came from
query string // that created the Stmt
stickyErr error // if non-nil, this error is returned for all operations
// If in a transaction, else both nil:
tx *Tx
txsi driver.Stmt
mu sync.Mutex // protects the rest of the fields
closed bool
// css is a list of underlying driver statement interfaces
// that are valid on particular connections. This is only
// used if tx == nil and one is found that has idle
// connections. If tx != nil, txsi is always used.
css []connStmt
}
// Exec executes a prepared statement with the given arguments and
// returns a Result summarizing the effect of the statement.
func (s *Stmt) Exec(args ...interface{}) (Result, error) {
_, releaseConn, si, err := s.connStmt()
if err != nil {
return nil, err
}
defer releaseConn()
// -1 means the driver doesn't know how to count the number of
// placeholders, so we won't sanity check input here and instead let the
// driver deal with errors.
if want := si.NumInput(); want != -1 && len(args) != want {
return nil, fmt.Errorf("sql: expected %d arguments, got %d", want, len(args))
}
// Convert args to subset types.
if cc, ok := si.(driver.ColumnConverter); ok {
for n, arg := range args {
args[n], err = cc.ColumnConverter(n).ConvertValue(arg)
if err != nil {
return nil, fmt.Errorf("sql: converting Exec argument #%d's type: %v", n, err)
}
if !driver.IsParameterSubsetType(args[n]) {
return nil, fmt.Errorf("sql: driver ColumnConverter error converted %T to unsupported type %T",
arg, args[n])
}
}
} else {
for n, arg := range args {
args[n], err = driver.DefaultParameterConverter.ConvertValue(arg)
if err != nil {
return nil, fmt.Errorf("sql: converting Exec argument #%d's type: %v", n, err)
}
}
}
resi, err := si.Exec(args)
if err != nil {
return nil, err
}
return result{resi}, nil
}
// connStmt returns a free driver connection on which to execute the
// statement, a function to call to release the connection, and a
// statement bound to that connection.
func (s *Stmt) connStmt() (ci driver.Conn, releaseConn func(), si driver.Stmt, err error) {
if err = s.stickyErr; err != nil {
return
}
s.mu.Lock()
if s.closed {
s.mu.Unlock()
err = errors.New("sql: statement is closed")
return
}
// In a transaction, we always use the connection that the
// transaction was created on.
if s.tx != nil {
s.mu.Unlock()
ci, err = s.tx.grabConn() // blocks, waiting for the connection.
if err != nil {
return
}
releaseConn = func() { s.tx.releaseConn() }
return ci, releaseConn, s.txsi, nil
}
var cs connStmt
match := false
for _, v := range s.css {
// TODO(bradfitz): lazily clean up entries in this
// list with dead conns while enumerating
if _, match = s.db.connIfFree(cs.ci); match {
cs = v
break
}
}
s.mu.Unlock()
// Make a new conn if all are busy.
// TODO(bradfitz): or wait for one? make configurable later?
if !match {
ci, err := s.db.conn()
if err != nil {
return nil, nil, nil, err
}
si, err := ci.Prepare(s.query)
if err != nil {
return nil, nil, nil, err
}
s.mu.Lock()
cs = connStmt{ci, si}
s.css = append(s.css, cs)
s.mu.Unlock()
}
conn := cs.ci
releaseConn = func() { s.db.putConn(conn) }
return conn, releaseConn, cs.si, nil
}
// Query executes a prepared query statement with the given arguments
// and returns the query results as a *Rows.
func (s *Stmt) Query(args ...interface{}) (*Rows, error) {
ci, releaseConn, si, err := s.connStmt()
if err != nil {
return nil, err
}
// -1 means the driver doesn't know how to count the number of
// placeholders, so we won't sanity check input here and instead let the
// driver deal with errors.
if want := si.NumInput(); want != -1 && len(args) != want {
return nil, fmt.Errorf("sql: statement expects %d inputs; got %d", si.NumInput(), len(args))
}
sargs, err := subsetTypeArgs(args)
if err != nil {
return nil, err
}
rowsi, err := si.Query(sargs)
if err != nil {
s.db.putConn(ci)
return nil, err
}
// Note: ownership of ci passes to the *Rows, to be freed
// with releaseConn.
rows := &Rows{
db: s.db,
ci: ci,
releaseConn: releaseConn,
rowsi: rowsi,
}
return rows, nil
}
// QueryRow executes a prepared query statement with the given arguments.
// If an error occurs during the execution of the statement, that error will
// be returned by a call to Scan on the returned *Row, which is always non-nil.
// If the query selects no rows, the *Row's Scan will return ErrNoRows.
// Otherwise, the *Row's Scan scans the first selected row and discards
// the rest.
//
// Example usage:
//
// var name string
// err := nameByUseridStmt.QueryRow(id).Scan(&s)
func (s *Stmt) QueryRow(args ...interface{}) *Row {
rows, err := s.Query(args...)
if err != nil {
return &Row{err: err}
}
return &Row{rows: rows}
}
// Close closes the statement.
func (s *Stmt) Close() error {
if s.stickyErr != nil {
return s.stickyErr
}
s.mu.Lock()
defer s.mu.Unlock()
if s.closed {
return nil
}
s.closed = true
if s.tx != nil {
s.txsi.Close()
} else {
for _, v := range s.css {
if ci, match := s.db.connIfFree(v.ci); match {
v.si.Close()
s.db.putConn(ci)
} else {
// TODO(bradfitz): care that we can't close
// this statement because the statement's
// connection is in use?
}
}
}
return nil
}
// Rows is the result of a query. Its cursor starts before the first row
// of the result set. Use Next to advance through the rows:
//
// rows, err := db.Query("SELECT ...")
// ...
// for rows.Next() {
// var id int
// var name string
// err = rows.Scan(&id, &name)
// ...
// }
// err = rows.Err() // get any error encountered during iteration
// ...
type Rows struct {
db *DB
ci driver.Conn // owned; must call putconn when closed to release
releaseConn func()
rowsi driver.Rows
closed bool
lastcols []interface{}
lasterr error
closeStmt *Stmt // if non-nil, statement to Close on close
}
// Next prepares the next result row for reading with the Scan method.
// It returns true on success, false if there is no next result row.
// Every call to Scan, even the first one, must be preceded by a call
// to Next.
func (rs *Rows) Next() bool {
if rs.closed {
return false
}
if rs.lasterr != nil {
return false
}
if rs.lastcols == nil {
rs.lastcols = make([]interface{}, len(rs.rowsi.Columns()))
}
rs.lasterr = rs.rowsi.Next(rs.lastcols)
if rs.lasterr == io.EOF {
rs.Close()
}
return rs.lasterr == nil
}
// Err returns the error, if any, that was encountered during iteration.
func (rs *Rows) Err() error {
if rs.lasterr == io.EOF {
return nil
}
return rs.lasterr
}
// Columns returns the column names.
// Columns returns an error if the rows are closed, or if the rows
// are from QueryRow and there was a deferred error.
func (rs *Rows) Columns() ([]string, error) {
if rs.closed {
return nil, errors.New("sql: Rows are closed")
}
if rs.rowsi == nil {
return nil, errors.New("sql: no Rows available")
}
return rs.rowsi.Columns(), nil
}
// Scan copies the columns in the current row into the values pointed
// at by dest. If dest contains pointers to []byte, the slices should
// not be modified and should only be considered valid until the next
// call to Next or Scan.
func (rs *Rows) Scan(dest ...interface{}) error {
if rs.closed {
return errors.New("sql: Rows closed")
}
if rs.lasterr != nil {
return rs.lasterr
}
if rs.lastcols == nil {
return errors.New("sql: Scan called without calling Next")
}
if len(dest) != len(rs.lastcols) {
return fmt.Errorf("sql: expected %d destination arguments in Scan, not %d", len(rs.lastcols), len(dest))
}
for i, sv := range rs.lastcols {
err := convertAssign(dest[i], sv)
if err != nil {
return fmt.Errorf("sql: Scan error on column index %d: %v", i, err)
}
}
return nil
}
// Close closes the Rows, preventing further enumeration. If the
// end is encountered, the Rows are closed automatically. Close
// is idempotent.
func (rs *Rows) Close() error {
if rs.closed {
return nil
}
rs.closed = true
err := rs.rowsi.Close()
rs.releaseConn()
if rs.closeStmt != nil {
rs.closeStmt.Close()
}
return err
}
// Row is the result of calling QueryRow to select a single row.
type Row struct {
// One of these two will be non-nil:
err error // deferred error for easy chaining
rows *Rows
}
// Scan copies the columns from the matched row into the values
// pointed at by dest. If more than one row matches the query,
// Scan uses the first row and discards the rest. If no row matches
// the query, Scan returns ErrNoRows.
func (r *Row) Scan(dest ...interface{}) error {
if r.err != nil {
return r.err
}
defer r.rows.Close()
if !r.rows.Next() {
return ErrNoRows
}
err := r.rows.Scan(dest...)
if err != nil {
return err
}
// TODO(bradfitz): for now we need to defensively clone all
// []byte that the driver returned, since we're about to close
// the Rows in our defer, when we return from this function.
// the contract with the driver.Next(...) interface is that it
// can return slices into read-only temporary memory that's
// only valid until the next Scan/Close. But the TODO is that
// for a lot of drivers, this copy will be unnecessary. We
// should provide an optional interface for drivers to
// implement to say, "don't worry, the []bytes that I return
// from Next will not be modified again." (for instance, if
// they were obtained from the network anyway) But for now we
// don't care.
for _, dp := range dest {
b, ok := dp.(*[]byte)
if !ok {
continue
}
clone := make([]byte, len(*b))
copy(clone, *b)
*b = clone
}
return nil
}
// A Result summarizes an executed SQL command.
type Result interface {
LastInsertId() (int64, error)
RowsAffected() (int64, error)
}
type result struct {
driver.Result
}
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