Merge pull request #340 from r-dbi/f-13-savepoint

- `dbBegin()`, `dbCommit()` and `dbRollback()` gain `name` argument to support savepoints. An unnamed transaction must be started beforehand (#13).

R/transactions.R

@@ -27,35 +27,53 @@
 NULL
 
 #' @export
+#' @param name If provided, uses the `SAVEPOINT` SQL syntax
+#'   to establish, remove (commit) or undo a ßsavepoint.
 #' @rdname postgres-transactions
-setMethod("dbBegin", "PqConnection", function(conn, ...) {
-  if (connection_is_transacting(conn@ptr)) {
-    stop("Nested transactions not supported.", call. = FALSE)
+setMethod("dbBegin", "PqConnection", function(conn, ..., name = NULL) {
+  if (is.null(name)) {
+    if (connection_is_transacting(conn@ptr)) {
+      stop("Nested transactions not supported.", call. = FALSE)
+    }
+    dbExecute(conn, "BEGIN")
+    connection_set_transacting(conn@ptr, TRUE)
+  } else {
+    if (!connection_is_transacting(conn@ptr)) {
+      stop("Savepoints require an active transaction.", call. = FALSE)
+    }
+    dbExecute(conn, paste0("SAVEPOINT ", dbQuoteIdentifier(conn, name)))
   }
-
-  dbExecute(conn, "BEGIN")
-  connection_set_transacting(conn@ptr, TRUE)
   invisible(TRUE)
 })
 
 #' @export
 #' @rdname postgres-transactions
-setMethod("dbCommit", "PqConnection", function(conn, ...) {
-  if (!connection_is_transacting(conn@ptr)) {
-    stop("Call dbBegin() to start a transaction.", call. = FALSE)
+setMethod("dbCommit", "PqConnection", function(conn, ..., name = NULL) {
+  if (is.null(name)) {
+    if (!connection_is_transacting(conn@ptr)) {
+      stop("Call dbBegin() to start a transaction.", call. = FALSE)
+    }
+    dbExecute(conn, "COMMIT")
+    connection_set_transacting(conn@ptr, FALSE)
+  } else {
+    dbExecute(conn, paste0("RELEASE SAVEPOINT ", dbQuoteIdentifier(conn, name)))
   }
-  dbExecute(conn, "COMMIT")
-  connection_set_transacting(conn@ptr, FALSE)
   invisible(TRUE)
 })
 
 #' @export
 #' @rdname postgres-transactions
-setMethod("dbRollback", "PqConnection", function(conn, ...) {
-  if (!connection_is_transacting(conn@ptr)) {
-    stop("Call dbBegin() to start a transaction.", call. = FALSE)
+setMethod("dbRollback", "PqConnection", function(conn, ..., name = NULL) {
+  if (is.null(name)) {
+    if (!connection_is_transacting(conn@ptr)) {
+      stop("Call dbBegin() to start a transaction.", call. = FALSE)
+    }
+    dbExecute(conn, "ROLLBACK")
+    connection_set_transacting(conn@ptr, FALSE)
+  } else {
+    name_quoted <- dbQuoteIdentifier(conn, name)
+    dbExecute(conn, paste0("ROLLBACK TO ", name_quoted))
+    dbExecute(conn, paste0("RELEASE SAVEPOINT ", name_quoted))
   }
-  dbExecute(conn, "ROLLBACK")
-  connection_set_transacting(conn@ptr, FALSE)
   invisible(TRUE)
 })

R/utils.R

@@ -17,3 +17,7 @@ stopc <- function(...) {
 warningc <- function(...) {
   warning(..., call. = FALSE, domain = NA)
 }
+
+try_silent <- function(code) {
+  tryCatch(code, error = function(e) invisible())
+}