import "database/sql/driver"
Package driver defines interfaces to be implemented by database drivers as used by package sql.
Most code should use package sql.
The driver interface has evolved over time. Drivers should implement Connector and DriverContext interfaces. The Connector.Connect and Driver.Open methods should never return ErrBadConn. ErrBadConn should only be returned from Validator, SessionResetter, or a query method if the connection is already in an invalid (e.g. closed) state.
All Conn implementations should implement the following interfaces: Pinger, SessionResetter, and Validator.
If named parameters or context are supported, the driver's Conn should implement: ExecerContext, QueryerContext, ConnPrepareContext, and ConnBeginTx.
To support custom data types, implement NamedValueChecker. NamedValueChecker also allows queries to accept per-query options as a parameter by returning ErrRemoveArgument from CheckNamedValue.
If multiple result sets are supported, Rows should implement RowsNextResultSet. If the driver knows how to describe the types present in the returned result it should implement the following interfaces: RowsColumnTypeScanType, RowsColumnTypeDatabaseTypeName, RowsColumnTypeLength, RowsColumnTypeNullable, and RowsColumnTypePrecisionScale. A given row value may also return a Rows type, which may represent a database cursor value.
Before a connection is returned to the connection pool after use, IsValid is called if implemented. Before a connection is reused for another query, ResetSession is called if implemented. If a connection is never returned to the connection pool but immediately reused, then ResetSession is called prior to reuse but IsValid is not called.
var Bool boolType
Bool is a ValueConverter that converts input values to bools.
The conversion rules are:
var DefaultParameterConverter defaultConverter
DefaultParameterConverter is the default implementation of ValueConverter that's used when a Stmt doesn't implement ColumnConverter.
DefaultParameterConverter returns its argument directly if IsValue(arg). Otherwise, if the argument implements Valuer, its Value method is used to return a Value. As a fallback, the provided argument's underlying type is used to convert it to a Value: underlying integer types are converted to int64, floats to float64, bool, string, and []byte to themselves. If the argument is a nil pointer, ConvertValue returns a nil Value. If the argument is a non-nil pointer, it is dereferenced and ConvertValue is called recursively. Other types are an error.
var ErrBadConn = errors.New("driver: bad connection")
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.
Errors will be checked using errors.Is. An error may wrap ErrBadConn or implement the Is(error) bool method.
var ErrRemoveArgument = errors.New("driver: remove argument from query")
ErrRemoveArgument may be returned from NamedValueChecker to instruct the sql package to not pass the argument to the driver query interface. Return when accepting query specific options or structures that aren't SQL query arguments.
var ErrSkip = errors.New("driver: skip fast-path; continue as if unimplemented")
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 Int32 int32Type
Int32 is a ValueConverter that converts input values to int64, respecting the limits of an int32 value.
var ResultNoRows noRows
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 String stringType
String is a ValueConverter that converts its input to a string. If the value is already a string or []byte, it's unchanged. If the value is of another type, conversion to string is done with fmt.Sprintf("%v", v).
func IsScanValue(v any) bool
IsScanValue is equivalent to IsValue. It exists for compatibility.
func IsValue(v any) bool
IsValue reports whether v is a valid Value parameter type.
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
}
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.
Deprecated: Drivers should implement NamedValueChecker.
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.
//
// Drivers must ensure all network calls made by Close
// do not block indefinitely (e.g. apply a timeout).
Close() error
// Begin starts and returns a new transaction.
//
// Deprecated: Drivers should implement ConnBeginTx instead (or additionally).
Begin() (Tx, error)
}
Conn is a connection to a database. It is not used concurrently by multiple goroutines.
Conn is assumed to be stateful.
type ConnBeginTx interface {
// BeginTx starts and returns a new transaction.
// If the context is canceled by the user the sql package will
// call Tx.Rollback before discarding and closing the connection.
//
// This must check opts.Isolation to determine if there is a set
// isolation level. If the driver does not support a non-default
// level and one is set or if there is a non-default isolation level
// that is not supported, an error must be returned.
//
// This must also check opts.ReadOnly to determine if the read-only
// value is true to either set the read-only transaction property if supported
// or return an error if it is not supported.
BeginTx(ctx context.Context, opts TxOptions) (Tx, error)
}
ConnBeginTx enhances the Conn interface with context and TxOptions.
type ConnPrepareContext interface {
// PrepareContext returns a prepared statement, bound to this connection.
// context is for the preparation of the statement,
// it must not store the context within the statement itself.
PrepareContext(ctx context.Context, query string) (Stmt, error)
}
ConnPrepareContext enhances the Conn interface with context.
type Connector interface {
// Connect returns a connection to the database.
// Connect 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 provided context.Context is for dialing purposes only
// (see net.DialContext) and should not be stored or used for
// other purposes. A default timeout should still be used
// when dialing as a connection pool may call Connect
// asynchronously to any query.
//
// The returned connection is only used by one goroutine at a
// time.
Connect(context.Context) (Conn, error)
// Driver returns the underlying Driver of the Connector,
// mainly to maintain compatibility with the Driver method
// on sql.DB.
Driver() Driver
}
A Connector represents a driver in a fixed configuration and can create any number of equivalent Conns for use by multiple goroutines.
A Connector can be passed to sql.OpenDB, to allow drivers to implement their own sql.DB constructors, or returned by DriverContext's OpenConnector method, to allow drivers access to context and to avoid repeated parsing of driver configuration.
If a Connector implements io.Closer, the sql package's DB.Close method will call Close and return error (if any).
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)
}
Driver is the interface that must be implemented by a database driver.
Database drivers may implement DriverContext for access to contexts and to parse the name only once for a pool of connections, instead of once per connection.
type DriverContext interface {
// OpenConnector must parse the name in the same format that Driver.Open
// parses the name parameter.
OpenConnector(name string) (Connector, error)
}
If a Driver implements DriverContext, then sql.DB will call OpenConnector to obtain a Connector and then invoke that Connector's Connect method to obtain each needed connection, instead of invoking the Driver's Open method for each connection. The two-step sequence allows drivers to parse the name just once and also provides access to per-Conn contexts.
type Execer interface {
Exec(query string, args []Value) (Result, error)
}
Execer is an optional interface that may be implemented by a Conn.
If a Conn implements neither ExecerContext nor Execer, the sql package's DB.Exec will first prepare a query, execute the statement, and then close the statement.
Exec may return ErrSkip.
Deprecated: Drivers should implement ExecerContext instead.
type ExecerContext interface {
ExecContext(ctx context.Context, query string, args []NamedValue) (Result, error)
}
ExecerContext is an optional interface that may be implemented by a Conn.
If a Conn does not implement ExecerContext, the sql package's DB.Exec will fall back to Execer; if the Conn does not implement Execer either, DB.Exec will first prepare a query, execute the statement, and then close the statement.
ExecContext may return ErrSkip.
ExecContext must honor the context timeout and return when the context is canceled.
type IsolationLevel int
IsolationLevel is the transaction isolation level stored in TxOptions.
This type should be considered identical to sql.IsolationLevel along with any values defined on it.
type NamedValue struct {
// If the Name is not empty it should be used for the parameter identifier and
// not the ordinal position.
//
// Name will not have a symbol prefix.
Name string
// Ordinal position of the parameter starting from one and is always set.
Ordinal int
// Value is the parameter value.
Value Value
}
NamedValue holds both the value name and value.
type NamedValueChecker interface {
// CheckNamedValue is called before passing arguments to the driver
// and is called in place of any ColumnConverter. CheckNamedValue must do type
// validation and conversion as appropriate for the driver.
CheckNamedValue(*NamedValue) error
}
NamedValueChecker may be optionally implemented by Conn or Stmt. It provides the driver more control to handle Go and database types beyond the default Values types allowed.
The sql package checks for value checkers in the following order, stopping at the first found match: Stmt.NamedValueChecker, Conn.NamedValueChecker, Stmt.ColumnConverter, DefaultParameterConverter.
If CheckNamedValue returns ErrRemoveArgument, the NamedValue will not be included in the final query arguments. This may be used to pass special options to the query itself.
If ErrSkip is returned the column converter error checking path is used for the argument. Drivers may wish to return ErrSkip after they have exhausted their own special cases.
type NotNull struct {
Converter ValueConverter
}
NotNull is a type that implements ValueConverter by disallowing nil values but otherwise delegating to another ValueConverter.
func (n NotNull) ConvertValue(v any) (Value, error)
type Null struct {
Converter ValueConverter
}
Null is a type that implements ValueConverter by allowing nil values but otherwise delegating to another ValueConverter.
func (n Null) ConvertValue(v any) (Value, error)
type Pinger interface {
Ping(ctx context.Context) error
}
Pinger is an optional interface that may be implemented by a Conn.
If a Conn does not implement Pinger, the sql package's DB.Ping and DB.PingContext will check if there is at least one Conn available.
If Conn.Ping returns ErrBadConn, DB.Ping and DB.PingContext will remove the Conn from pool.
type Queryer interface {
Query(query string, args []Value) (Rows, error)
}
Queryer is an optional interface that may be implemented by a Conn.
If a Conn implements neither QueryerContext nor Queryer, the sql package's DB.Query will first prepare a query, execute the statement, and then close the statement.
Query may return ErrSkip.
Deprecated: Drivers should implement QueryerContext instead.
type QueryerContext interface {
QueryContext(ctx context.Context, query string, args []NamedValue) (Rows, error)
}
QueryerContext is an optional interface that may be implemented by a Conn.
If a Conn does not implement QueryerContext, the sql package's DB.Query will fall back to Queryer; if the Conn does not implement Queryer either, DB.Query will first prepare a query, execute the statement, and then close the statement.
QueryContext may return ErrSkip.
QueryContext must honor the context timeout and return when the context is canceled.
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)
}
Result is the result of a query execution.
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.
//
// Next should return io.EOF when there are no more rows.
//
// The dest should not be written to outside of Next. Care
// should be taken when closing Rows not to modify
// a buffer held in dest.
Next(dest []Value) error
}
Rows is an iterator over an executed query's results.
type RowsAffected int64
RowsAffected implements Result for an INSERT or UPDATE operation which mutates a number of rows.
func (RowsAffected) LastInsertId() (int64, error)
func (v RowsAffected) RowsAffected() (int64, error)
type RowsColumnTypeDatabaseTypeName interface {
Rows
ColumnTypeDatabaseTypeName(index int) string
}
RowsColumnTypeDatabaseTypeName may be implemented by Rows. It should return the database system type name without the length. Type names should be uppercase. Examples of returned types: "VARCHAR", "NVARCHAR", "VARCHAR2", "CHAR", "TEXT", "DECIMAL", "SMALLINT", "INT", "BIGINT", "BOOL", "[]BIGINT", "JSONB", "XML", "TIMESTAMP".
type RowsColumnTypeLength interface {
Rows
ColumnTypeLength(index int) (length int64, ok bool)
}
RowsColumnTypeLength may be implemented by Rows. It should return the length of the column type if the column is a variable length type. If the column is not a variable length type ok should return false. If length is not limited other than system limits, it should return math.MaxInt64. The following are examples of returned values for various types:
TEXT (math.MaxInt64, true) varchar(10) (10, true) nvarchar(10) (10, true) decimal (0, false) int (0, false) bytea(30) (30, true)
type RowsColumnTypeNullable interface {
Rows
ColumnTypeNullable(index int) (nullable, ok bool)
}
RowsColumnTypeNullable may be implemented by Rows. The nullable value should be true if it is known the column may be null, or false if the column is known to be not nullable. If the column nullability is unknown, ok should be false.
type RowsColumnTypePrecisionScale interface {
Rows
ColumnTypePrecisionScale(index int) (precision, scale int64, ok bool)
}
RowsColumnTypePrecisionScale may be implemented by Rows. It should return the precision and scale for decimal types. If not applicable, ok should be false. The following are examples of returned values for various types:
decimal(38, 4) (38, 4, true) int (0, 0, false) decimal (math.MaxInt64, math.MaxInt64, true)
type RowsColumnTypeScanType interface {
Rows
ColumnTypeScanType(index int) reflect.Type
}
RowsColumnTypeScanType may be implemented by Rows. It should return the value type that can be used to scan types into. For example, the database column type "bigint" this should return "reflect.TypeOf(int64(0))".
type RowsNextResultSet interface {
Rows
// HasNextResultSet is called at the end of the current result set and
// reports whether there is another result set after the current one.
HasNextResultSet() bool
// NextResultSet advances the driver to the next result set even
// if there are remaining rows in the current result set.
//
// NextResultSet should return io.EOF when there are no more result sets.
NextResultSet() error
}
RowsNextResultSet extends the Rows interface by providing a way to signal the driver to advance to the next result set.
type SessionResetter interface {
// ResetSession is called prior to executing a query on the connection
// if the connection has been used before. If the driver returns ErrBadConn
// the connection is discarded.
ResetSession(ctx context.Context) error
}
SessionResetter may be implemented by Conn to allow drivers to reset the session state associated with the connection and to signal a bad connection.
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.
//
// Drivers must ensure all network calls made by Close
// do not block indefinitely (e.g. apply a timeout).
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.
//
// Deprecated: Drivers should implement StmtExecContext instead (or additionally).
Exec(args []Value) (Result, error)
// Query executes a query that may return rows, such as a
// SELECT.
//
// Deprecated: Drivers should implement StmtQueryContext instead (or additionally).
Query(args []Value) (Rows, error)
}
Stmt is a prepared statement. It is bound to a Conn and not used by multiple goroutines concurrently.
type StmtExecContext interface {
// ExecContext executes a query that doesn't return rows, such
// as an INSERT or UPDATE.
//
// ExecContext must honor the context timeout and return when it is canceled.
ExecContext(ctx context.Context, args []NamedValue) (Result, error)
}
StmtExecContext enhances the Stmt interface by providing Exec with context.
type StmtQueryContext interface {
// QueryContext executes a query that may return rows, such as a
// SELECT.
//
// QueryContext must honor the context timeout and return when it is canceled.
QueryContext(ctx context.Context, args []NamedValue) (Rows, error)
}
StmtQueryContext enhances the Stmt interface by providing Query with context.
type Tx interface {
Commit() error
Rollback() error
}
Tx is a transaction.
type TxOptions struct {
Isolation IsolationLevel
ReadOnly bool
}
TxOptions holds the transaction options.
This type should be considered identical to sql.TxOptions.
type Validator interface {
// IsValid is called prior to placing the connection into the
// connection pool. The connection will be discarded if false is returned.
IsValid() bool
}
Validator may be implemented by Conn to allow drivers to signal if a connection is valid or if it should be discarded.
If implemented, drivers may return the underlying error from queries, even if the connection should be discarded by the connection pool.
type Value any
Value is a value that drivers must be able to handle. It is either nil, a type handled by a database driver's NamedValueChecker interface, or an instance of one of these types:
int64 float64 bool []byte string time.Time
If the driver supports cursors, a returned Value may also implement the Rows interface in this package. This is used, for example, when a user selects a cursor such as "select cursor(select * from my_table) from dual". If the Rows from the select is closed, the cursor Rows will also be closed.
type ValueConverter interface {
// ConvertValue converts a value to a driver Value.
ConvertValue(v any) (Value, error)
}
ValueConverter is the interface providing the ConvertValue method.
Various implementations of ValueConverter are provided by the driver package to provide consistent implementations of conversions between drivers. The ValueConverters have several uses:
type Valuer interface {
// Value returns a driver Value.
// Value must not panic.
Value() (Value, error)
}
Valuer is the interface providing the Value method.
Types implementing Valuer interface are able to convert themselves to a driver Value.