database/sql/driver: API cleanups

-- add driver.Value type and documentation,
   convert from interface{} to Value where
   appropriate.
-- don't say "subset" anywhere,
-- SubsetValuer -> Valuer
-- SubsetValue -> Value
-- IsParameterSubsetType -> IsValue
-- IsScanSubsetType -> IsScanValue

Fixes #2842

R=golang-dev, r, rsc
CC=golang-dev
https://golang.org/cl/5674084

src/pkg/database/sql/convert.go

@@ -17,8 +17,8 @@ import (
 // subsetTypeArgs takes a slice of arguments from callers of the sql
 // package and converts them into a slice of the driver package's
 // "subset types".
-func subsetTypeArgs(args []interface{}) ([]interface{}, error) {
-	out := make([]interface{}, len(args))
+func subsetTypeArgs(args []interface{}) ([]driver.Value, error) {
+	out := make([]driver.Value, len(args))
 	for n, arg := range args {
 		var err error
 		out[n], err = driver.DefaultParameterConverter.ConvertValue(arg)

src/pkg/database/sql/driver/driver.go

@@ -6,21 +6,20 @@
 // drivers as used by package sql.
 //
 // Most code should use package sql.
-//
-// Drivers only need to be aware of a subset of Go's types.  The sql package
-// will convert all types into one of the following:
+package driver
+
+import "errors"
+
+// A driver Value is a value that drivers must be able to handle.
+// A Value is either nil or an instance of one of these types:
 //
 //   int64
 //   float64
 //   bool
-//   nil
 //   []byte
 //   string   [*] everywhere except from Rows.Next.
 //   time.Time
-//
-package driver
-
-import "errors"
+type Value interface{}
 
 // Driver is the interface that must be implemented by a database
 // driver.
@@ -50,11 +49,9 @@ var ErrSkip = errors.New("driver: skip fast-path; continue as if unimplemented")
 // first prepare a query, execute the statement, and then close the
 // statement.
 //
-// All arguments are of a subset type as defined in the package docs.
-//
 // Exec may return ErrSkip.
 type Execer interface {
-	Exec(query string, args []interface{}) (Result, error)
+	Exec(query string, args []Value) (Result, error)
 }
 
 // Conn is a connection to a database. It is not used concurrently
@@ -127,18 +124,17 @@ type Stmt interface {
 	NumInput() int
 
 	// Exec executes a query that doesn't return rows, such
-	// as an INSERT or UPDATE.  The args are all of a subset
-	// type as defined above.
-	Exec(args []interface{}) (Result, error)
+	// as an INSERT or UPDATE.
+	Exec(args []Value) (Result, error)
 
 	// Exec executes a query that may return rows, such as a
-	// SELECT.  The args of all of a subset type as defined above.
-	Query(args []interface{}) (Rows, error)
+	// SELECT.
+	Query(args []Value) (Rows, error)
 }
 
 // ColumnConverter may be optionally implemented by Stmt if the
 // the statement is aware of its own columns' types and can
-// convert from any type to a driver subset type.
+// 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
@@ -162,12 +158,12 @@ type Rows interface {
 	// the provided slice. The provided slice will be the same
 	// size as the Columns() are wide.
 	//
-	// The dest slice may be populated with only with values
-	// of subset types defined above, but excluding string.
+	// 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 []interface{}) error
+	Next(dest []Value) error
 }
 
 // Tx is a transaction.
@@ -190,18 +186,19 @@ func (v RowsAffected) RowsAffected() (int64, error) {
 	return int64(v), nil
 }
 
-// DDLSuccess is a pre-defined Result for drivers to return when a DDL
-// command succeeds.
-var DDLSuccess ddlSuccess
+// 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 ddlSuccess struct{}
+type noRows struct{}
 
-var _ Result = ddlSuccess{}
+var _ Result = noRows{}
 
-func (ddlSuccess) LastInsertId() (int64, error) {
+func (noRows) LastInsertId() (int64, error) {
 	return 0, errors.New("no LastInsertId available after DDL statement")
 }
 
-func (ddlSuccess) RowsAffected() (int64, error) {
+func (noRows) RowsAffected() (int64, error) {
 	return 0, errors.New("no RowsAffected available after DDL statement")
 }

src/pkg/database/sql/driver/types.go

@@ -17,28 +17,28 @@ import (
 // driver package to provide consistent implementations of conversions
 // between drivers.  The ValueConverters have several uses:
 //
-//  * converting from the subset types as provided by the sql package
+//  * converting from the Value types as provided by the sql package
 //    into a database table's specific column type and making sure it
 //    fits, such as making sure a particular int64 fits in a
 //    table's uint16 column.
 //
 //  * converting a value as given from the database into one of the
-//    subset types.
+//    driver Value types.
 //
-//  * by the sql package, for converting from a driver's subset type
+//  * by the sql package, for converting from a driver's Value type
 //    to a user's type in a scan.
 type ValueConverter interface {
-	// ConvertValue converts a value to a restricted subset type.
-	ConvertValue(v interface{}) (interface{}, error)
+	// ConvertValue converts a value to a driver Value.
+	ConvertValue(v interface{}) (Value, error)
 }
 
-// SubsetValuer is the interface providing the SubsetValue method.
+// Valuer is the interface providing the Value method.
 //
-// Types implementing SubsetValuer interface are able to convert
-// themselves to one of the driver's allowed subset values.
-type SubsetValuer interface {
-	// SubsetValue returns a driver parameter subset value.
-	SubsetValue() (interface{}, error)
+// Types implementing Valuer interface are able to convert
+// themselves to a driver Value.
+type Valuer interface {
+	// Value returns a driver Value.
+	Value() (Value, error)
 }
 
 // Bool is a ValueConverter that converts input values to bools.
@@ -59,7 +59,7 @@ var _ ValueConverter = boolType{}
 
 func (boolType) String() string { return "Bool" }
 
-func (boolType) ConvertValue(src interface{}) (interface{}, error) {
+func (boolType) ConvertValue(src interface{}) (Value, error) {
 	switch s := src.(type) {
 	case bool:
 		return s, nil
@@ -104,7 +104,7 @@ type int32Type struct{}
 
 var _ ValueConverter = int32Type{}
 
-func (int32Type) ConvertValue(v interface{}) (interface{}, error) {
+func (int32Type) ConvertValue(v interface{}) (Value, error) {
 	rv := reflect.ValueOf(v)
 	switch rv.Kind() {
 	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
@@ -137,7 +137,7 @@ var String stringType
 
 type stringType struct{}
 
-func (stringType) ConvertValue(v interface{}) (interface{}, error) {
+func (stringType) ConvertValue(v interface{}) (Value, error) {
 	switch v.(type) {
 	case string, []byte:
 		return v, nil
@@ -151,7 +151,7 @@ type Null struct {
 	Converter ValueConverter
 }
 
-func (n Null) ConvertValue(v interface{}) (interface{}, error) {
+func (n Null) ConvertValue(v interface{}) (Value, error) {
 	if v == nil {
 		return nil, nil
 	}
@@ -164,28 +164,17 @@ type NotNull struct {
 	Converter ValueConverter
 }
 
-func (n NotNull) ConvertValue(v interface{}) (interface{}, error) {
+func (n NotNull) ConvertValue(v interface{}) (Value, error) {
 	if v == nil {
 		return nil, fmt.Errorf("nil value not allowed")
 	}
 	return n.Converter.ConvertValue(v)
 }
 
-// IsParameterSubsetType reports whether v is of a valid type for a
-// parameter. These types are:
-//
-//   int64
-//   float64
-//   bool
-//   nil
-//   []byte
-//   time.Time
-//   string
-//
-// This is the same list as IsScanSubsetType, with the addition of
-// string.
-func IsParameterSubsetType(v interface{}) bool {
-	if IsScanSubsetType(v) {
+// IsValue reports whether v is a valid Value parameter type.
+// Unlike IsScanValue, IsValue permits the string type.
+func IsValue(v interface{}) bool {
+	if IsScanValue(v) {
 		return true
 	}
 	if _, ok := v.(string); ok {
@@ -194,18 +183,9 @@ func IsParameterSubsetType(v interface{}) bool {
 	return false
 }
 
-// IsScanSubsetType reports whether v is of a valid type for a
-// value populated by Rows.Next. These types are:
-//
-//   int64
-//   float64
-//   bool
-//   nil
-//   []byte
-//   time.Time
-//
-// This is the same list as IsParameterSubsetType, without string.
-func IsScanSubsetType(v interface{}) bool {
+// IsScanValue reports whether v is a valid Value scan type.
+// Unlike IsValue, IsScanValue does not permit the string type.
+func IsScanValue(v interface{}) bool {
 	if v == nil {
 		return true
 	}
@@ -221,7 +201,7 @@ func IsScanSubsetType(v interface{}) bool {
 // ColumnConverter.
 //
 // DefaultParameterConverter returns the given value directly if
-// IsSubsetType(value).  Otherwise integer type are converted to
+// IsValue(value).  Otherwise integer type are converted to
 // int64, floats to float64, and strings to []byte.  Other types are
 // an error.
 var DefaultParameterConverter defaultConverter
@@ -230,18 +210,18 @@ type defaultConverter struct{}
 
 var _ ValueConverter = defaultConverter{}
 
-func (defaultConverter) ConvertValue(v interface{}) (interface{}, error) {
-	if IsParameterSubsetType(v) {
+func (defaultConverter) ConvertValue(v interface{}) (Value, error) {
+	if IsValue(v) {
 		return v, nil
 	}
 
-	if svi, ok := v.(SubsetValuer); ok {
-		sv, err := svi.SubsetValue()
+	if svi, ok := v.(Valuer); ok {
+		sv, err := svi.Value()
 		if err != nil {
 			return nil, err
 		}
-		if !IsParameterSubsetType(sv) {
-			return nil, fmt.Errorf("non-subset type %T returned from SubsetValue", sv)
+		if !IsValue(sv) {
+			return nil, fmt.Errorf("non-Value type %T returned from Value", sv)
 		}
 		return sv, nil
 	}

src/pkg/database/sql/fakedb_test.go

@@ -217,7 +217,7 @@ func (c *fakeConn) Close() error {
 	return nil
 }
 
-func checkSubsetTypes(args []interface{}) error {
+func checkSubsetTypes(args []driver.Value) error {
 	for n, arg := range args {
 		switch arg.(type) {
 		case int64, float64, bool, nil, []byte, string, time.Time:
@@ -228,7 +228,7 @@ func checkSubsetTypes(args []interface{}) error {
 	return nil
 }
 
-func (c *fakeConn) Exec(query string, args []interface{}) (driver.Result, error) {
+func (c *fakeConn) Exec(query string, args []driver.Value) (driver.Result, error) {
 	// This is an optional interface, but it's implemented here
 	// just to check that all the args of of the proper types.
 	// ErrSkip is returned so the caller acts as if we didn't
@@ -379,7 +379,7 @@ func (s *fakeStmt) Close() error {
 
 var errClosed = errors.New("fakedb: statement has been closed")
 
-func (s *fakeStmt) Exec(args []interface{}) (driver.Result, error) {
+func (s *fakeStmt) Exec(args []driver.Value) (driver.Result, error) {
 	if s.closed {
 		return nil, errClosed
 	}
@@ -392,12 +392,12 @@ func (s *fakeStmt) Exec(args []interface{}) (driver.Result, error) {
 	switch s.cmd {
 	case "WIPE":
 		db.wipe()
-		return driver.DDLSuccess, nil
+		return driver.ResultNoRows, nil
 	case "CREATE":
 		if err := db.createTable(s.table, s.colName, s.colType); err != nil {
 			return nil, err
 		}
-		return driver.DDLSuccess, nil
+		return driver.ResultNoRows, nil
 	case "INSERT":
 		return s.execInsert(args)
 	}
@@ -405,7 +405,7 @@ func (s *fakeStmt) Exec(args []interface{}) (driver.Result, error) {
 	return nil, fmt.Errorf("unimplemented statement Exec command type of %q", s.cmd)
 }
 
-func (s *fakeStmt) execInsert(args []interface{}) (driver.Result, error) {
+func (s *fakeStmt) execInsert(args []driver.Value) (driver.Result, error) {
 	db := s.c.db
 	if len(args) != s.placeholders {
 		panic("error in pkg db; should only get here if size is correct")
@@ -441,7 +441,7 @@ func (s *fakeStmt) execInsert(args []interface{}) (driver.Result, error) {
 	return driver.RowsAffected(1), nil
 }
 
-func (s *fakeStmt) Query(args []interface{}) (driver.Rows, error) {
+func (s *fakeStmt) Query(args []driver.Value) (driver.Rows, error) {
 	if s.closed {
 		return nil, errClosed
 	}
@@ -548,7 +548,7 @@ func (rc *rowsCursor) Columns() []string {
 	return rc.cols
 }
 
-func (rc *rowsCursor) Next(dest []interface{}) error {
+func (rc *rowsCursor) Next(dest []driver.Value) error {
 	if rc.closed {
 		return errors.New("fakedb: cursor is closed")
 	}

src/pkg/database/sql/sql.go

@@ -62,8 +62,8 @@ func (ns *NullString) Scan(value interface{}) error {
 	return convertAssign(&ns.String, value)
 }
 
-// SubsetValue implements the driver SubsetValuer interface.
-func (ns NullString) SubsetValue() (interface{}, error) {
+// Value implements the driver Valuer interface.
+func (ns NullString) Value() (driver.Value, error) {
 	if !ns.Valid {
 		return nil, nil
 	}
@@ -88,8 +88,8 @@ func (n *NullInt64) Scan(value interface{}) error {
 	return convertAssign(&n.Int64, value)
 }
 
-// SubsetValue implements the driver SubsetValuer interface.
-func (n NullInt64) SubsetValue() (interface{}, error) {
+// Value implements the driver Valuer interface.
+func (n NullInt64) Value() (driver.Value, error) {
 	if !n.Valid {
 		return nil, nil
 	}
@@ -114,8 +114,8 @@ func (n *NullFloat64) Scan(value interface{}) error {
 	return convertAssign(&n.Float64, value)
 }
 
-// SubsetValue implements the driver SubsetValuer interface.
-func (n NullFloat64) SubsetValue() (interface{}, error) {
+// Value implements the driver Valuer interface.
+func (n NullFloat64) Value() (driver.Value, error) {
 	if !n.Valid {
 		return nil, nil
 	}
@@ -140,8 +140,8 @@ func (n *NullBool) Scan(value interface{}) error {
 	return convertAssign(&n.Bool, value)
 }
 
-// SubsetValue implements the driver SubsetValuer interface.
-func (n NullBool) SubsetValue() (interface{}, error) {
+// Value implements the driver Valuer interface.
+func (n NullBool) Value() (driver.Value, error) {
 	if !n.Valid {
 		return nil, nil
 	}
@@ -523,8 +523,13 @@ func (tx *Tx) Exec(query string, args ...interface{}) (Result, error) {
 	}
 	defer tx.releaseConn()
 
+	sargs, err := subsetTypeArgs(args)
+	if err != nil {
+		return nil, err
+	}
+
 	if execer, ok := ci.(driver.Execer); ok {
-		resi, err := execer.Exec(query, args)
+		resi, err := execer.Exec(query, sargs)
 		if err == nil {
 			return result{resi}, nil
 		}
@@ -539,11 +544,6 @@ func (tx *Tx) Exec(query string, args ...interface{}) (Result, error) {
 	}
 	defer sti.Close()
 
-	sargs, err := subsetTypeArgs(args)
-	if err != nil {
-		return nil, err
-	}
-
 	resi, err := sti.Exec(sargs)
 	if err != nil {
 		return nil, err
@@ -618,19 +618,21 @@ func (s *Stmt) Exec(args ...interface{}) (Result, error) {
 		return nil, fmt.Errorf("sql: expected %d arguments, got %d", want, len(args))
 	}
 
+	sargs := make([]driver.Value, len(args))
+
 	// Convert args to subset types.
 	if cc, ok := si.(driver.ColumnConverter); ok {
 		for n, arg := range args {
 			// First, see if the value itself knows how to convert
 			// itself to a driver type.  For example, a NullString
 			// struct changing into a string or nil.
-			if svi, ok := arg.(driver.SubsetValuer); ok {
-				sv, err := svi.SubsetValue()
+			if svi, ok := arg.(driver.Valuer); ok {
+				sv, err := svi.Value()
 				if err != nil {
-					return nil, fmt.Errorf("sql: argument index %d from SubsetValue: %v", n, err)
+					return nil, fmt.Errorf("sql: argument index %d from Value: %v", n, err)
 				}
-				if !driver.IsParameterSubsetType(sv) {
-					return nil, fmt.Errorf("sql: argument index %d: non-subset type %T returned from SubsetValue", n, sv)
+				if !driver.IsValue(sv) {
+					return nil, fmt.Errorf("sql: argument index %d: non-subset type %T returned from Value", n, sv)
 				}
 				arg = sv
 			}
@@ -642,25 +644,25 @@ func (s *Stmt) Exec(args ...interface{}) (Result, error) {
 			// truncated), or that a nil can't go into a NOT NULL
 			// column before going across the network to get the
 			// same error.
-			args[n], err = cc.ColumnConverter(n).ConvertValue(arg)
+			sargs[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]) {
+			if !driver.IsValue(sargs[n]) {
 				return nil, fmt.Errorf("sql: driver ColumnConverter error converted %T to unsupported type %T",
-					arg, args[n])
+					arg, sargs[n])
 			}
 		}
 	} else {
 		for n, arg := range args {
-			args[n], err = driver.DefaultParameterConverter.ConvertValue(arg)
+			sargs[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)
+	resi, err := si.Exec(sargs)
 	if err != nil {
 		return nil, err
 	}
@@ -829,7 +831,7 @@ type Rows struct {
 	rowsi       driver.Rows
 
 	closed    bool
-	lastcols  []interface{}
+	lastcols  []driver.Value
 	lasterr   error
 	closeStmt *Stmt // if non-nil, statement to Close on close
 }
@@ -846,7 +848,7 @@ func (rs *Rows) Next() bool {
 		return false
 	}
 	if rs.lastcols == nil {
-		rs.lastcols = make([]interface{}, len(rs.rowsi.Columns()))
+		rs.lastcols = make([]driver.Value, len(rs.rowsi.Columns()))
 	}
 	rs.lasterr = rs.rowsi.Next(rs.lastcols)
 	if rs.lasterr == io.EOF {