database/sql: Add an optional Queryer-Interface (like Execer)

Completly the same like the Execer-Interface, just for Queries.
This allows Drivers to execute Queries without preparing them first

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/7085056

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

@@ -65,6 +65,17 @@ 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 db 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.
 //

src/pkg/database/sql/fakedb_test.go

@@ -266,6 +266,18 @@ func (c *fakeConn) Exec(query string, args []driver.Value) (driver.Result, error
 	return nil, driver.ErrSkip
 }
 
+func (c *fakeConn) Query(query string, args []driver.Value) (driver.Rows, error) {
+	// This is an optional interface, but it's implemented here
+	// just to check that all the args are of the proper types.
+	// ErrSkip is returned so the caller acts as if we didn't
+	// implement this at all.
+	err := checkSubsetTypes(args)
+	if err != nil {
+		return nil, err
+	}
+	return nil, driver.ErrSkip
+}
+
 func errf(msg string, args ...interface{}) error {
 	return errors.New("fakedb: " + fmt.Sprintf(msg, args...))
 }

src/pkg/database/sql/sql.go

@@ -328,6 +328,7 @@ func (db *DB) prepare(query string) (stmt *Stmt, err error) {
 }
 
 // Exec executes a query without returning any rows.
+// The args are for any placeholder parameters in the query.
 func (db *DB) Exec(query string, args ...interface{}) (Result, error) {
 	var res Result
 	var err error
@@ -375,16 +376,77 @@ func (db *DB) exec(query string, args []interface{}) (res Result, err error) {
 // Query executes a query that returns rows, typically a SELECT.
 // The args are for any placeholder parameters in the query.
 func (db *DB) Query(query string, args ...interface{}) (*Rows, error) {
-	stmt, err := db.Prepare(query)
+	var rows *Rows
+	var err error
+	for i := 0; i < 10; i++ {
+		rows, err = db.query(query, args)
+		if err != driver.ErrBadConn {
+			break
+		}
+	}
+	return rows, err
+}
+
+func (db *DB) query(query string, args []interface{}) (*Rows, error) {
+	ci, err := db.conn()
 	if err != nil {
 		return nil, err
 	}
-	rows, err := stmt.Query(args...)
+
+	releaseConn := func(err error) { db.putConn(ci, err) }
+
+	return db.queryConn(ci, releaseConn, query, args)
+}
+
+// queryConn executes a query on the given connection.
+// The connection gets released by the releaseConn function.
+func (db *DB) queryConn(ci driver.Conn, releaseConn func(error), query string, args []interface{}) (*Rows, error) {
+	if queryer, ok := ci.(driver.Queryer); ok {
+		dargs, err := driverArgs(nil, args)
 		if err != nil {
-		stmt.Close()
+			releaseConn(err)
 			return nil, err
 		}
-	rows.closeStmt = stmt
+		rowsi, err := queryer.Query(query, dargs)
+		if err != driver.ErrSkip {
+			if err != nil {
+				releaseConn(err)
+				return nil, err
+			}
+			// Note: ownership of ci passes to the *Rows, to be freed
+			// with releaseConn.
+			rows := &Rows{
+				db:          db,
+				ci:          ci,
+				releaseConn: releaseConn,
+				rowsi:       rowsi,
+			}
+			return rows, nil
+		}
+	}
+
+	sti, err := ci.Prepare(query)
+	if err != nil {
+		releaseConn(err)
+		return nil, err
+	}
+
+	rowsi, err := rowsiFromStatement(sti, args...)
+	if err != nil {
+		releaseConn(err)
+		sti.Close()
+		return nil, err
+	}
+
+	// Note: ownership of ci passes to the *Rows, to be freed
+	// with releaseConn.
+	rows := &Rows{
+		db:          db,
+		ci:          ci,
+		releaseConn: releaseConn,
+		rowsi:       rowsi,
+		closeStmt:   sti,
+	}
 	return rows, nil
 }
 
@@ -605,20 +667,14 @@ func (tx *Tx) Exec(query string, args ...interface{}) (Result, error) {
 
 // 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, ErrTxDone
-	}
-	stmt, err := tx.Prepare(query)
+	ci, err := tx.grabConn()
 	if err != nil {
 		return nil, err
 	}
-	rows, err := stmt.Query(args...)
-	if err != nil {
-		stmt.Close()
-		return nil, err
-	}
-	rows.closeStmt = stmt
-	return rows, err
+
+	releaseConn := func(err error) { tx.releaseConn() }
+
+	return tx.db.queryConn(ci, releaseConn, query, args)
 }
 
 // QueryRow executes a query that is expected to return at most one row.
@@ -762,6 +818,24 @@ func (s *Stmt) Query(args ...interface{}) (*Rows, error) {
 		return nil, err
 	}
 
+	rowsi, err := rowsiFromStatement(si, args...)
+	if err != nil {
+		releaseConn(err)
+		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
+}
+
+func rowsiFromStatement(si driver.Stmt, args ...interface{}) (driver.Rows, error) {
 	// -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.
@@ -776,18 +850,9 @@ func (s *Stmt) Query(args ...interface{}) (*Rows, error) {
 
 	rowsi, err := si.Query(dargs)
 	if err != nil {
-		releaseConn(err)
 		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
+	return rowsi, nil
 }
 
 // QueryRow executes a prepared query statement with the given arguments.
@@ -860,7 +925,7 @@ type Rows struct {
 	closed    bool
 	lastcols  []driver.Value
 	lasterr   error
-	closeStmt *Stmt // if non-nil, statement to Close on close
+	closeStmt driver.Stmt // if non-nil, statement to Close on close
 }
 
 // Next prepares the next result row for reading with the Scan method.