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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 driver defines interfaces to be implemented by database
// drivers as used by package sql.
//
// Most code should use package sql.
package driver
import "errors"
// Value is a value that drivers must be able to handle.
// It is either nil or an instance of one of these types:
//
// int64
// float64
// bool
// []byte
// string [*] everywhere except from Rows.Next.
// time.Time
type Value interface{}
// Driver is the interface that must be implemented by a database
// driver.
type Driver interface {
// Open returns a new connection to the database.
// The name is a string in a driver-specific format.
//
// Open may return a cached connection (one previously
// closed), but doing so is unnecessary; the sql package
// maintains a pool of idle connections for efficient re-use.
//
// The returned connection is only used by one goroutine at a
// time.
Open(name string) (Conn, error)
}
// ErrSkip may be returned by some optional interfaces' methods to
// indicate at runtime that the fast path is unavailable and the sql
// package should continue as if the optional interface was not
// implemented. ErrSkip is only supported where explicitly
// documented.
var ErrSkip = errors.New("driver: skip fast-path; continue as if unimplemented")
// ErrBadConn should be returned by a driver to signal to the sql
// package that a driver.Conn is in a bad state (such as the server
// having earlier closed the connection) and the sql package should
// retry on a new connection.
//
// To prevent duplicate operations, ErrBadConn should NOT be returned
// if there's a possibility that the database server might have
// performed the operation. Even if the server sends back an error,
// you shouldn't return ErrBadConn.
var ErrBadConn = errors.New("driver: bad connection")
// Execer is an optional interface that may be implemented by a Conn.
//
// If a Conn does not implement Execer, the sql package's DB.Exec will
// first prepare a query, execute the statement, and then close the
// statement.
//
// Exec may return ErrSkip.
type Execer interface {
Exec(query string, args []Value) (Result, error)
}
// Queryer is an optional interface that may be implemented by a Conn.
//
// If a Conn does not implement Queryer, the sql package's DB.Query will
// first prepare a query, execute the statement, and then close the
// statement.
//
// Query may return ErrSkip.
type Queryer interface {
Query(query string, args []Value) (Rows, error)
}
// Conn is a connection to a database. It is not used concurrently
// by multiple goroutines.
//
// Conn is assumed to be stateful.
type Conn interface {
// Prepare returns a prepared statement, bound to this connection.
Prepare(query string) (Stmt, error)
// Close invalidates and potentially stops any current
// prepared statements and transactions, marking this
// connection as no longer in use.
//
// Because the sql package maintains a free pool of
// connections and only calls Close when there's a surplus of
// idle connections, it shouldn't be necessary for drivers to
// do their own connection caching.
Close() error
// Begin starts and returns a new transaction.
Begin() (Tx, error)
}
// Result is the result of a query execution.
type Result interface {
// LastInsertId returns the database's auto-generated ID
// after, for example, an INSERT into a table with primary
// key.
LastInsertId() (int64, error)
// RowsAffected returns the number of rows affected by the
// query.
RowsAffected() (int64, error)
}
// Stmt is a prepared statement. It is bound to a Conn and not
// used by multiple goroutines concurrently.
type Stmt interface {
// Close closes the statement.
//
// As of Go 1.1, a Stmt will not be closed if it's in use
// by any queries.
Close() error
// NumInput returns the number of placeholder parameters.
//
// If NumInput returns >= 0, the sql package will sanity check
// argument counts from callers and return errors to the caller
// before the statement's Exec or Query methods are called.
//
// NumInput may also return -1, if the driver doesn't know
// its number of placeholders. In that case, the sql package
// will not sanity check Exec or Query argument counts.
NumInput() int
// Exec executes a query that doesn't return rows, such
// as an INSERT or UPDATE.
Exec(args []Value) (Result, error)
// Query executes a query that may return rows, such as a
// SELECT.
Query(args []Value) (Rows, error)
}
// ColumnConverter may be optionally implemented by Stmt if the
// statement is aware of its own columns' types and can convert from
// any type to a driver Value.
type ColumnConverter interface {
// ColumnConverter returns a ValueConverter for the provided
// column index. If the type of a specific column isn't known
// or shouldn't be handled specially, DefaultValueConverter
// can be returned.
ColumnConverter(idx int) ValueConverter
}
// Rows is an iterator over an executed query's results.
type Rows interface {
// Columns returns the names of the columns. The number of
// columns of the result is inferred from the length of the
// slice. If a particular column name isn't known, an empty
// string should be returned for that entry.
Columns() []string
// Close closes the rows iterator.
Close() error
// Next is called to populate the next row of data into
// the provided slice. The provided slice will be the same
// size as the Columns() are wide.
//
// The dest slice may be populated only with
// a driver Value type, but excluding string.
// All string values must be converted to []byte.
//
// Next should return io.EOF when there are no more rows.
Next(dest []Value) error
}
// Tx is a transaction.
type Tx interface {
Commit() error
Rollback() error
}
// RowsAffected implements Result for an INSERT or UPDATE operation
// which mutates a number of rows.
type RowsAffected int64
var _ Result = RowsAffected(0)
func (RowsAffected) LastInsertId() (int64, error) {
return 0, errors.New("no LastInsertId available")
}
func (v RowsAffected) RowsAffected() (int64, error) {
return int64(v), nil
}
// ResultNoRows is a pre-defined Result for drivers to return when a DDL
// command (such as a CREATE TABLE) succeeds. It returns an error for both
// LastInsertId and RowsAffected.
var ResultNoRows noRows
type noRows struct{}
var _ Result = noRows{}
func (noRows) LastInsertId() (int64, error) {
return 0, errors.New("no LastInsertId available after DDL statement")
}
func (noRows) RowsAffected() (int64, error) {
return 0, errors.New("no RowsAffected available after DDL statement")
}