feat: support MySQL FOR SHARE with OF, NOWAIT, SKIP LOCKED option through with_for_up...

diff --git a/doc/build/changelog/unreleased_20/12964.rst b/doc/build/changelog/unreleased_20/12964.rst
new file mode 100644 (file)
index 0000000..12073ec
--- /dev/null
+++ b/doc/build/changelog/unreleased_20/12964.rst
@@ -0,0 +1,8 @@
+.. change::
+    :tags: bug, mysql
+    :tickets: 12964
+
+    Resolved MySQL 8 ``FOR SHARE`` compilation so that
+    :meth:`_sql.Select.with_for_update` emits ``FOR SHARE`` (with ``OF``,
+    ``NOWAIT`` and ``SKIP LOCKED`` modifiers) when supported, while maintaining
+    ``LOCK IN SHARE MODE`` for older MySQL versions.

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 1c51302ba2a03dfd8a106766df16bd70f402d048..de5f0ccd391a80c2cc11d63e3c67095482154682 100644 (file)
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -1781,7 +1781,10 @@ class MySQLCompiler(compiler.SQLCompiler):
     ) -> str:
         assert select._for_update_arg is not None
         if select._for_update_arg.read:
-            tmp = " LOCK IN SHARE MODE"
+            if self.dialect.supports_for_share:
+                tmp = " FOR SHARE"
+            else:
+                tmp = " LOCK IN SHARE MODE"
         else:
             tmp = " FOR UPDATE"
 
@@ -2735,6 +2738,7 @@ class MySQLDialect(default.DefaultDialect):
     sequences_optional = False
 
     supports_for_update_of = False  # default for MySQL ...
+    supports_for_share = False  # default for MySQL ...
     # ... may be updated to True for MySQL 8+ in initialize()
 
     _requires_alias_for_on_duplicate_key = False  # Only available ...
@@ -3194,6 +3198,10 @@ class MySQLDialect(default.DefaultDialect):
             self._is_mysql and self.server_version_info >= (8,)
         )
 
+        self.supports_for_share = (
+            self._is_mysql and self.server_version_info >= (8,)
+        )
+
         self._needs_correct_for_88718_96365 = (
             not self.is_mariadb and self.server_version_info >= (8,)
         )

diff --git a/test/dialect/mysql/test_for_update.py b/test/dialect/mysql/test_for_update.py
index 5c26d8eb6d5a009ece7ceeb3c2061e51ee25fd6c..e9594108dd9500b10e2a180ca20cbd663fca31c1 100644 (file)
--- a/test/dialect/mysql/test_for_update.py
+++ b/test/dialect/mysql/test_for_update.py
@@ -196,6 +196,10 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
     for_update_of_dialect = mysql.dialect()
     for_update_of_dialect.server_version_info = (8, 0, 0)
     for_update_of_dialect.supports_for_update_of = True
+    for_update_of_dialect.supports_for_share = True
+    for_share_dialect = mysql.dialect()
+    for_share_dialect.server_version_info = (8, 0, 0)
+    for_share_dialect.supports_for_share = True
 
     def test_for_update_basic(self):
         self.assert_compile(
@@ -215,6 +219,16 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "FROM mytable WHERE mytable.myid = %s LOCK IN SHARE MODE",
         )
 
+    def test_for_update_read_mysql80(self):
+        self.assert_compile(
+            self.table1.select()
+            .where(self.table1.c.myid == 7)
+            .with_for_update(read=True),
+            "SELECT mytable.myid, mytable.name, mytable.description "
+            "FROM mytable WHERE mytable.myid = %s FOR SHARE",
+            dialect=self.for_share_dialect,
+        )
+
     def test_for_update_skip_locked(self):
         self.assert_compile(
             self.table1.select()
@@ -235,6 +249,17 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "LOCK IN SHARE MODE SKIP LOCKED",
         )
 
+    def test_for_update_read_skip_locked_mysql80(self):
+        self.assert_compile(
+            self.table1.select()
+            .where(self.table1.c.myid == 7)
+            .with_for_update(read=True, skip_locked=True),
+            "SELECT mytable.myid, mytable.name, mytable.description "
+            "FROM mytable WHERE mytable.myid = %s "
+            "FOR SHARE SKIP LOCKED",
+            dialect=self.for_share_dialect,
+        )
+
     def test_for_update_nowait(self):
         self.assert_compile(
             self.table1.select()
@@ -255,6 +280,17 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
             "LOCK IN SHARE MODE NOWAIT",
         )
 
+    def test_for_update_read_nowait_mysql80(self):
+        self.assert_compile(
+            self.table1.select()
+            .where(self.table1.c.myid == 7)
+            .with_for_update(read=True, nowait=True),
+            "SELECT mytable.myid, mytable.name, mytable.description "
+            "FROM mytable WHERE mytable.myid = %s "
+            "FOR SHARE NOWAIT",
+            dialect=self.for_share_dialect,
+        )
+
     def test_for_update_of_nowait(self):
         self.assert_compile(
             self.table1.select()
@@ -340,7 +376,7 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
             .with_for_update(read=True, of=self.table1, nowait=True),
             "SELECT mytable.myid, mytable.name, mytable.description "
             "FROM mytable WHERE mytable.myid = %s "
-            "LOCK IN SHARE MODE OF mytable NOWAIT",
+            "FOR SHARE OF mytable NOWAIT",
             dialect=self.for_update_of_dialect,
         )
 
@@ -351,7 +387,7 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
             .with_for_update(read=True, of=self.table1, skip_locked=True),
             "SELECT mytable.myid, mytable.name, mytable.description "
             "FROM mytable WHERE mytable.myid = %s "
-            "LOCK IN SHARE MODE OF mytable SKIP LOCKED",
+            "FOR SHARE OF mytable SKIP LOCKED",
             dialect=self.for_update_of_dialect,
         )
 
@@ -366,7 +402,7 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
             ),
             "SELECT mytable.myid, mytable.name, mytable.description "
             "FROM mytable WHERE mytable.myid = %s "
-            "LOCK IN SHARE MODE OF mytable NOWAIT",
+            "FOR SHARE OF mytable NOWAIT",
             dialect=self.for_update_of_dialect,
         )
 
@@ -377,7 +413,7 @@ class MySQLForUpdateCompileTest(fixtures.TestBase, AssertsCompiledSQL):
             .with_for_update(read=True, of=self.table1),
             "SELECT mytable.myid, mytable.name, mytable.description "
             "FROM mytable WHERE mytable.myid = %s "
-            "LOCK IN SHARE MODE OF mytable",
+            "FOR SHARE OF mytable",
             dialect=self.for_update_of_dialect,
         )