Add named argument to transaction functions.

#41

NEWS

@@ -1,5 +1,8 @@
 Version 0.11.6.9000
 
+- `dbBegin()`, `dbCommit()` and `dbRollback()` gain a named argument to
+  specify named savepoints.
+
 - Remove SqliteObject and dbObject classes, modifying SqliteDriver, 
   SqliteConnection, and SqliteResult to use composition instead of multiple
   inheritance.

R/ConnectionTransactions.R

@@ -12,6 +12,8 @@ NULL
 #' 
 #' @param conn a \code{\linkS4class{SQLiteConnection}} object, produced by
 #'   \code{\link[DBI]{dbConnect}}
+#' @param name Supply a name to use a named savepoint. This allows you to
+#'   nest multiple transaction
 #' @return A boolean, indicating success or failure.
 #' @examples
 #' con <- dbConnect(SQLite(), ":memory:")
@@ -34,27 +36,47 @@ NULL
 #' dbCommit(con)
 #' dbGetQuery(con, "SELECT count(*) FROM arrests")[1, ]
 #' 
+#' # Named savepoints can be nested --------------------------------------------
+#' dbBegin(con, "a")
+#' dbBegin(con, "b")
+#' dbRollback(con, "b")
+#' dbCommit(con, "a")
+#' 
 #' dbDisconnect(con)
 #' @name transactions
 NULL
 
 #' @export
 #' @rdname transactions
-setMethod("dbBegin", "SQLiteConnection", function(conn) {
-  dbGetQuery(conn, "BEGIN")
+setMethod("dbBegin", "SQLiteConnection", function(conn, name = NULL) {
+  if (is.null(name)) {
+    dbGetQuery(conn, "BEGIN")  
+  } else {
+    dbGetQuery(conn, paste("SAVEPOINT ", name))
+  }
+
   TRUE
 })
 
 #' @export
 #' @rdname transactions
-setMethod("dbCommit", "SQLiteConnection", function(conn) {
-  dbGetQuery(conn, "COMMIT")
+setMethod("dbCommit", "SQLiteConnection", function(conn, name = NULL) {
+  if (is.null(name)) {
+    dbGetQuery(conn, "COMMIT")
+  } else {
+    dbGetQuery(conn, paste("RELEASE SAVEPOINT ", name))
+  }
+
   TRUE
 })
 
 #' @export
 #' @rdname transactions
-setMethod("dbRollback", "SQLiteConnection", function(conn) {
-  dbGetQuery(conn, "ROLLBACK")
+setMethod("dbRollback", "SQLiteConnection", function(conn, name = NULL) {
+  if (is.null(name)) {
+    dbGetQuery(conn, "ROLLBACK")
+  } else {
+    dbGetQuery(conn, paste("ROLLBACK TO ", name))
+  }
   TRUE
 })

man/transactions.Rd

@@ -7,15 +7,18 @@
 \alias{transactions}
 \title{SQLite transaction management.}
 \usage{
-\S4method{dbBegin}{SQLiteConnection}(conn)
+\S4method{dbBegin}{SQLiteConnection}(conn, name = NULL)
 
-\S4method{dbCommit}{SQLiteConnection}(conn)
+\S4method{dbCommit}{SQLiteConnection}(conn, name = NULL)
 
-\S4method{dbRollback}{SQLiteConnection}(conn)
+\S4method{dbRollback}{SQLiteConnection}(conn, name = NULL)
 }
 \arguments{
 \item{conn}{a \code{\linkS4class{SQLiteConnection}} object, produced by
 \code{\link[DBI]{dbConnect}}}
+
+\item{name}{Supply a name to use a named savepoint. This allows you to
+nest multiple transaction}
 }
 \value{
 A boolean, indicating success or failure.
@@ -47,6 +50,12 @@ dbClearResult(rs)
 dbCommit(con)
 dbGetQuery(con, "SELECT count(*) FROM arrests")[1, ]
 
+# Named savepoints can be nested --------------------------------------------
+dbBegin(con, "a")
+dbBegin(con, "b")
+dbRollback(con, "b")
+dbCommit(con, "a")
+
 dbDisconnect(con)
 }