Add SKIP LOCKED support for Postgresql, Oracle

This adds `SELECT ... FOR UPDATE SKIP LOCKED`/
`SELECT ... FOR SHARE SKIP LOCKED` rendering.

Change-Id: Id1dc4f1cafc1de23f397a6f73d54ab2c58d5910d
Pull-request: https://bitbucket.org/zzzeek/sqlalchemy/pull-requests/86

4 files changed, 22 insertions, 5 deletions

diff --git a/lib/sqlalchemy/dialects/oracle/base.py b/lib/sqlalchemy/dialects/oracle/base.py
index 6992670c4..493bf362f 100644
--- a/lib/sqlalchemy/dialects/oracle/base.py
+++ b/lib/sqlalchemy/dialects/oracle/base.py
@@ -814,6 +814,8 @@ class OracleCompiler(compiler.SQLCompiler):
 
         if select._for_update_arg.nowait:
             tmp += " NOWAIT"
+        if select._for_update_arg.skip_locked:
+            tmp += " SKIP LOCKED"
 
         return tmp
 
diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index 136cb1b28..1bc4409f2 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -1185,6 +1185,8 @@ class PGCompiler(compiler.SQLCompiler):
 
         if select._for_update_arg.nowait:
             tmp += " NOWAIT"
+        if select._for_update_arg.skip_locked:
+            tmp += " SKIP LOCKED"
 
         return tmp
 
diff --git a/lib/sqlalchemy/orm/query.py b/lib/sqlalchemy/orm/query.py
index 34daa707f..7fab33197 100644
--- a/lib/sqlalchemy/orm/query.py
+++ b/lib/sqlalchemy/orm/query.py
@@ -1397,7 +1397,8 @@ class Query(object):
         self._for_update_arg = LockmodeArg.parse_legacy_query(mode)
 
     @_generative()
-    def with_for_update(self, read=False, nowait=False, of=None):
+    def with_for_update(self, read=False, nowait=False, of=None,
+                        skip_locked=False):
         """return a new :class:`.Query` with the specified options for the
         ``FOR UPDATE`` clause.
 
@@ -1425,7 +1426,8 @@ class Query(object):
             full argument and behavioral description.
 
         """
-        self._for_update_arg = LockmodeArg(read=read, nowait=nowait, of=of)
+        self._for_update_arg = LockmodeArg(read=read, nowait=nowait, of=of,
+                                           skip_locked=skip_locked)
 
     @_generative()
     def params(self, *args, **kwargs):
diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index e299f067e..bd1d04e57 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -1723,14 +1723,16 @@ class ForUpdateArg(ClauseElement):
         if self.of is not None:
             self.of = [clone(col, **kw) for col in self.of]
 
-    def __init__(self, nowait=False, read=False, of=None):
+    def __init__(self, nowait=False, read=False, of=None, skip_locked=False):
         """Represents arguments specified to :meth:`.Select.for_update`.
 
         .. versionadded:: 0.9.0
+
         """
 
         self.nowait = nowait
         self.read = read
+        self.skip_locked = skip_locked
         if of is not None:
             self.of = [_interpret_as_column_or_from(elem)
                        for elem in util.to_list(of)]
@@ -1873,7 +1875,8 @@ class GenerativeSelect(SelectBase):
         self._for_update_arg = ForUpdateArg.parse_legacy_select(value)
 
     @_generative
-    def with_for_update(self, nowait=False, read=False, of=None):
+    def with_for_update(self, nowait=False, read=False, of=None,
+                        skip_locked=False):
         """Specify a ``FOR UPDATE`` clause for this :class:`.GenerativeSelect`.
 
         E.g.::
@@ -1908,10 +1911,18 @@ class GenerativeSelect(SelectBase):
          and Oracle.  May render as a table or as a column depending on
          backend.
 
+        :param skip_locked: boolean, will render ``FOR UPDATE SKIP LOCKED``
+         on Oracle and Postgresql dialects or ``FOR SHARE SKIP LOCKED`` if
+         ``read=True`` is also specified.
+
+         .. versionadded:: 1.1.0
+
         .. versionadded:: 0.9.0
 
+
         """
-        self._for_update_arg = ForUpdateArg(nowait=nowait, read=read, of=of)
+        self._for_update_arg = ForUpdateArg(nowait=nowait, read=read, of=of,
+                                            skip_locked=skip_locked)
 
     @_generative
     def apply_labels(self):