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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 (
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"runtime"
"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("db: Register driver is nil")
}
if _, dup := drivers[name]; dup {
panic("db: 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.
}
// 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("db: 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
freeConn []driver.Conn
}
// 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("db: unknown driver %q (forgotten import?)", driverName)
}
return &DB{driver: driver, dsn: dataSourceName}, nil
}
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) {
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db.mu.Lock()
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) {
if n := len(db.freeConn); n < db.maxIdleConns() {
db.freeConn = append(db.freeConn, c)
return
}
db.closeConn(c)
}
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) {
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// Optional fast path, if the driver implements driver.Execer.
if execer, ok := db.driver.(driver.Execer); ok {
resi, err := execer.Exec(query, args)
if err != nil {
return nil, err
}
return result{resi}, nil
}
// If the driver does not implement driver.Execer, we need
// a connection.
conn, err := db.conn()
if err != nil {
return nil, err
}
defer db.putConn(conn)
if execer, ok := conn.(driver.Execer); ok {
resi, err := execer.Exec(query, args)
if err != nil {
return nil, err
}
return result{resi}, nil
}
sti, err := conn.Prepare(query)
if err != nil {
return nil, err
}
defer sti.Close()
resi, err := sti.Exec(args)
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
}
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 (db *DB) QueryRow(query string, args ...interface{}) *Row {
rows, err := db.Query(query, args...)
if err != nil {
return &Row{err: err}
}
return &Row{rows: rows}
}
// Begin starts a transaction. The isolation level is dependent on
// the driver.
func (db *DB) Begin() (*Tx, error) {
// TODO(bradfitz): add another method for beginning a transaction
// at a specific isolation level.
panic(todo())
}
// DriverDatabase returns the database's underlying driver.
func (db *DB) Driver() driver.Driver {
return db.driver
}
// Tx is an in-progress database transaction.
type Tx struct {
}
// Commit commits the transaction.
panic(todo())
}
// Rollback aborts the transaction.
panic(todo())
}
// Prepare creates a prepared statement.
func (tx *Tx) Prepare(query string) (*Stmt, error) {
panic(todo())
}
// Exec executes a query that doesn't return rows.
// For example: an INSERT and UPDATE.
func (tx *Tx) Exec(query string, args ...interface{}) {
panic(todo())
}
// Query executes a query that returns rows, typically a SELECT.
func (tx *Tx) Query(query string, args ...interface{}) (*Rows, error) {
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panic(todo())
}
// 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 {
panic(todo())
}
// 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 Sttm
mu sync.Mutex
closed bool
css []connStmt // can use any that have idle connections
}
func todo() string {
_, file, line, _ := runtime.Caller(1)
return fmt.Sprintf("%s:%d: TODO: implement", file, line)
}
// 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) {
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ci, si, err := s.connStmt()
if err != nil {
return nil, err
}
defer s.db.putConn(ci)
if want := si.NumInput(); len(args) != want {
return nil, fmt.Errorf("db: 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("db: converting Exec argument #%d's type: %v", n, err)
}
if !driver.IsParameterSubsetType(args[n]) {
return nil, fmt.Errorf("db: 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("db: converting Exec argument #%d's type: %v", n, err)
}
}
}
resi, err := si.Exec(args)
if err != nil {
return nil, err
}
return result{resi}, nil
}
func (s *Stmt) connStmt(args ...interface{}) (driver.Conn, driver.Stmt, error) {
s.mu.Lock()
if s.closed {
return nil, nil, errors.New("db: statement is closed")
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}
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, err
}
si, err := ci.Prepare(s.query)
if err != nil {
return nil, nil, err
}
s.mu.Lock()
cs = connStmt{ci, si}
s.css = append(s.css, cs)
s.mu.Unlock()
}
return cs.ci, 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) {
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ci, si, err := s.connStmt(args...)
if err != nil {
return nil, err
}
if len(args) != si.NumInput() {
return nil, fmt.Errorf("db: statement expects %d inputs; got %d", si.NumInput(), len(args))
}
rowsi, err := si.Query(args)
if err != nil {
s.db.putConn(ci)
return nil, err
}
// Note: ownership of ci passes to the *Rows
rows := &Rows{
db: s.db,
ci: ci,
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.
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s.mu.Lock()
defer s.mu.Unlock() // TODO(bradfitz): move this unlock after 'closed = true'?
if s.closed {
return nil
}
s.closed = true
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.Error() // get any Error encountered during iteration
// ...
type Rows struct {
db *DB
ci driver.Conn // owned; must be returned when Rows is closed
rowsi driver.Rows
closed bool
lastcols []interface{}
}
// 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)
return rs.lasterr == nil
}
// Error returns the error, if any, that was encountered during iteration.
func (rs *Rows) Error() error {
if rs.lasterr == io.EOF {
return nil
}
return rs.lasterr
}
// 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 {
return errors.New("db: Rows closed")
}
if rs.lasterr != nil {
return rs.lasterr
}
if rs.lastcols == nil {
return errors.New("db: Scan called without calling Next")
}
if len(dest) != len(rs.lastcols) {
return fmt.Errorf("db: 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("db: 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.
if rs.closed {
return nil
}
rs.closed = true
err := rs.rowsi.Close()
rs.db.putConn(rs.ci)
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.
//
// 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 (r *Row) Scan(dest ...interface{}) error {
if r.err != nil {
return r.err
}
defer r.rows.Close()
if !r.rows.Next() {
return ErrNoRows
}
return r.rows.Scan(dest...)
}
// A Result summarizes an executed SQL command.
type Result interface {
LastInsertId() (int64, error)
RowsAffected() (int64, error)
}
type result struct {
driver.Result
}