default implementation for dbListFields(DBIConnection, Id)

- Add default implementation for `dbListFields(DBIConnection, Id)`, this relies on `dbQuoteIdentifier(DBIConnection, Id)` (#75).

R/DBConnection.R

@@ -324,20 +324,32 @@ setGeneric("dbListFields",
 #' @export
 setMethod("dbListFields", signature("DBIConnection", "character"),
   function(conn, name, ...) {
-    rs <- dbSendQuery(
-      conn,
-      paste(
-        "SELECT * FROM ",
-        dbQuoteIdentifier(conn, name),
-        "LIMIT 0"
-      )
-    )
-    on.exit(dbClearResult(rs))
+    list_fields(conn, name)
+  }
+)
 
-    names(dbFetch(rs, n = 0, row.names = FALSE))
+#' @rdname hidden_aliases
+#' @export
+setMethod("dbListFields", signature("DBIConnection", "Id"),
+  function(conn, name, ...) {
+    list_fields(conn, name)
   }
 )
 
+list_fields <- function(conn, name) {
+  rs <- dbSendQuery(
+    conn,
+    paste(
+      "SELECT * FROM ",
+      dbQuoteIdentifier(conn, name),
+      "LIMIT 0"
+    )
+  )
+  on.exit(dbClearResult(rs))
+
+  names(dbFetch(rs, n = 0, row.names = FALSE))
+}
+
 #' List remote tables
 #'
 #' Returns the unquoted names of remote tables accessible through this