fix: close() nulls _pool + connect() lock (psql-7/8 twin), % in identifiers, doc caveats

close() now nulls self._pool so a closed instance reports not-connected instead of
masquerading as live (twin of psql-7); connect() is guarded by an internal asyncio.Lock
so concurrent connect() calls serialize instead of racing to create and orphan multiple
live pools (twin of psql-8). _quote_ident now escapes a literal % in identifiers (mysql-7:
PyMySQL's query % args substitution otherwise breaks any Layer-1 call against a %-bearing
table/column name). fetchval/exists tolerate a caller-overridden tuple cursorclass via a
new _first_value helper (mysql-8). Documents the %%-escaping rule for literal % in raw SQL
text (mysql-6) and the upsert() VALUES() deprecation on MySQL 8.0.20+ (mysql-9).

Signed-off-by: disqualifier <dev@disqualifier.me>

README.md

@@ -11,13 +11,13 @@ wire-compatible and share the driver, so this covers both.
 `requirements.txt`:
 
 ```
-mysql @ git+ssh://git@git.rethinkstudios.io/rethink-public/mysql.git@v0.1.3
+mysql @ git+ssh://git@git.rethinkstudios.io/rethink-public/mysql.git@v0.1.4
 ```
 
 Direct:
 
 ```bash
-pip install "mysql @ git+ssh://git@git.rethinkstudios.io/rethink-public/mysql.git@v0.1.3"
+pip install "mysql @ git+ssh://git@git.rethinkstudios.io/rethink-public/mysql.git@v0.1.4"
 ```
 
 Pulls `aiomysql` (which pulls `PyMySQL`).
@@ -99,7 +99,12 @@ For anything even Layer 2 doesn't model (`executemany`, server-side cursors), us
 - **Values are always parameterized.** Layer 1 builds `%s` internally; Layer 2 takes your
   `%s` placeholders + a params sequence. Never f-string/`%`-format a value into SQL (the
   `%s` is the DBAPI placeholder, not Python string formatting). Only identifiers
-  (table/column names) are interpolated, and they're backtick-quoted.
+  (table/column names) are interpolated, and they're backtick-quoted — Layer 1 also
+  escapes a literal `%` inside an identifier for you.
+- **A literal `%` in Layer-2 SQL text must be written `%%`.** PyMySQL builds the query via
+  `query % args` whenever you pass params, so `"... LIKE '%foo%'"` with params raises
+  `TypeError`/`ValueError` — write `"... LIKE '%%foo%%'"` instead. Calls with no params are
+  unaffected (no substitution happens), and Layer 1 handles this for you internally.
 
 ## Dialect vs psql
 
@@ -115,7 +120,8 @@ Layer 1 is portable — you never see these. A Layer-2 raw-SQL author does:
 
 `upsert()`'s returned rowcount follows MySQL's `ON DUPLICATE KEY UPDATE` convention (1 for
 an insert, 2 for an update, 0 for a no-op) — a per-row count that differs from psql's; treat
-it as "affected", not "rows matched".
+it as "affected", not "rows matched". It emits the `col = VALUES(col)` update form, which
+MySQL 8.0.20+ deprecates (warning 1287, still functional; MariaDB is unaffected).
 
 ## Error contract — fail loud
 
@@ -134,7 +140,10 @@ result (no row, empty table) — never a swallowed failure.
 
 `get`/`delete`/`exists`/`get_one` take **equality** conditions only (`col = val AND ...`);
 anything richer goes through Layer 2. The pool runs with `autocommit=True`; `transaction()`
-opens an explicit transaction for atomic multi-statement blocks.
+opens an explicit transaction for atomic multi-statement blocks. `cursorclass` is
+overridable via a constructor kwarg (default `DictCursor`); `fetchval`/`exists` work under
+either a dict or tuple cursorclass, everything else stays dict-shaped only under the
+default `DictCursor`.
 
 ## Versioning
 

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "mysql"
-version = "0.1.3"
+version = "0.1.4"
 description = "async mysql/mariadb wrapper over aiomysql: two-layer API (friendly verbs + raw escape hatch), fail-loud, config-free"
 requires-python = ">=3.10"
 dependencies = [

src/mysql/__init__.py

@@ -1,3 +1,5 @@
 from .mysql import MysqlDB
 
-__all__ = ["MysqlDB"]
+__version__ = "0.1.4"
+
+__all__ = ["MysqlDB", "__version__"]

src/mysql/mysql.py

@@ -33,18 +33,17 @@ call-site changes; only the dialect below differs, hidden inside the wrapper):
 
 dialect (mysql-specific; visible only in raw layer-2 SQL you write):
     - placeholders are `%s` (here) vs `$1` (psql). the `%s` is the DBAPI placeholder the
-      driver consumes, NOT python `%` string formatting.
-    - upsert emits `ON DUPLICATE KEY UPDATE` (here) vs `ON CONFLICT` (psql); layer-1
-      upsert() hides this.
+      driver consumes, NOT python `%` string formatting — but PyMySQL builds it via
+      `query % args` whenever params are passed, so any OTHER literal `%` in the query
+      text (e.g. `LIKE '%foo%'`) must be written `%%` or it raises. no params -> no
+      substitution -> a lone `%` is fine. layer 1 escapes `%` in identifiers for you.
+    - upsert emits `ON DUPLICATE KEY UPDATE` (here) vs `ON CONFLICT` (psql), via the
+      deprecated `col = VALUES(col)` form (MySQL 8.0.20+ warns; still works, MariaDB is
+      unaffected). layer-1 upsert() hides both.
 
 rows:
-    layer 1 and fetch/fetchone return plain dicts ({column: value}) via aiomysql's
-    DictCursor — identical shape to the psql lib.
-
-placeholders / injection safety:
-    values are ALWAYS parameterized — layer 1 builds `%s` internally; layer 2 takes your
-    `%s` placeholders + a params sequence. never f-string/%-format a value into SQL. only
-    identifiers (table/column names) are interpolated, and they are backtick-quoted.
+    layer 1 and fetch/fetchone return plain dicts via aiomysql's DictCursor (identical
+    shape to psql). fetchval/exists tolerate a caller-overridden tuple cursorclass too.
 
 errors (FAIL LOUD — unlike the mongo lib's swallow-and-default):
     every method catches the driver error (pymysql.err.MySQLError, OSError on connection
@@ -53,6 +52,7 @@ errors (FAIL LOUD — unlike the mongo lib's swallow-and-default):
     wrapped, use the raw `.pool` property (the aiomysql.Pool).
 """
 
+import asyncio
 import logging
 from typing import Any, Dict, List, Optional, Sequence
 
@@ -64,13 +64,27 @@ log = logging.getLogger(__name__)
 _DRIVER_ERRORS = (MySQLError, OSError)
 
 
+def _first_value(row) -> Any:
+    """return the first column's value from a dict or sequence row
+
+    fetchval/exists read a single scalar column and work under either cursorclass: the
+    default DictCursor (dict row) or a caller override to a tuple/sequence cursor via
+    pool_kwargs — the only two row shapes aiomysql cursors produce.
+    """
+    return next(iter(row.values())) if isinstance(row, dict) else row[0]
+
+
 def _quote_ident(identifier: str) -> str:
-    """backtick-quote a sql identifier (table/column), escaping embedded backticks
+    """backtick-quote a sql identifier (table/column), escaping backticks and `%`
 
     identifiers can't be parameterized, so they are interpolated — backtick-quoting +
-    doubling any embedded backtick is the mysql-safe way to do that for caller names.
+    doubling any embedded backtick is the mysql-safe way to do that for caller names. an
+    embedded `%` is also doubled: PyMySQL applies `query % args` whenever a call passes
+    params, and an unescaped `%` inside an interpolated identifier would hit that same
+    substitution and raise, not just literal `%` written by the caller (see the module
+    docstring's `%%`-escaping rule).
     """
-    return "`" + identifier.replace("`", "``") + "`"
+    return "`" + identifier.replace("`", "``").replace("%", "%%") + "`"
 
 
 class MysqlDB:
@@ -92,10 +106,15 @@ class MysqlDB:
 
         host/port/db/user/password/minsize/maxsize are injected by the caller. extra
         pool_kwargs pass through to aiomysql.create_pool (unix_socket, ssl, charset, ...).
-        rows come back as dicts (DictCursor), overridable via pool_kwargs. autocommit is
-        always on: layer-1 verbs and raw execute() rely on it to commit on their own, so
-        `autocommit=False` in pool_kwargs is rejected (use transaction() for atomic
-        multi-statement blocks instead — it disables autocommit for just that block).
+        rows come back as dicts (DictCursor), overridable via pool_kwargs to a tuple
+        cursorclass — fetchval/exists work either way, everything else stays dict-shaped
+        only under DictCursor. autocommit is always on: layer-1 verbs and raw execute()
+        rely on it to commit their own writes without an explicit commit, so
+        `autocommit=False` in pool_kwargs is rejected outright — silently accepting it
+        would mean every write sits uncommitted until something else commits or the
+        connection is returned to the pool and rolled back, losing data with no error.
+        use transaction() for an atomic multi-statement block instead (it disables
+        autocommit for just that block).
         """
         if pool_kwargs.get("autocommit") is False:
             raise ValueError(
@@ -116,6 +135,7 @@ class MysqlDB:
         self._config.setdefault("cursorclass", aiomysql.cursors.DictCursor)
         self._config.update(pool_kwargs)
         self._pool: Optional[aiomysql.Pool] = None
+        self._connect_lock = asyncio.Lock()
 
     async def connect(self) -> "MysqlDB":
         """build the pool and validate it with SELECT 1; fail loud on bad config
@@ -123,8 +143,11 @@ class MysqlDB:
         returns self so callers can write `db = await MysqlDB(...).connect()`. if called
         again on an already-connected instance the previous pool is closed first (no
         orphaned pool); if the SELECT-1 validation fails the freshly-built pool is torn
-        down before re-raising, so a failed connect() never leaks a live pool.
+        down before re-raising, so a failed connect() never leaks a live pool. concurrent
+        callers serialize on an internal lock so racing connect() calls build exactly one
+        pool instead of each leaking the losers' live pools.
         """
+        async with self._connect_lock:
             if self._pool is not None:
                 await self.close()
             pool = await aiomysql.create_pool(**self._config)
@@ -151,6 +174,8 @@ class MysqlDB:
         except _DRIVER_ERRORS:
             log.exception("mysql.close()")
             raise
+        finally:
+            self._pool = None
 
     async def __aenter__(self) -> "MysqlDB":
         return await self.connect()
@@ -234,7 +259,7 @@ class MysqlDB:
             raise
         if not row:
             return None
-        return next(iter(row.values()))
+        return _first_value(row)
 
     def transaction(self):
         """async context manager running a block of statements atomically
@@ -349,16 +374,19 @@ class MysqlDB:
         except _DRIVER_ERRORS:
             log.exception("mysql.exists(%s)", table)
             raise
-        return bool(next(iter(row.values()))) if row else False
+        return bool(_first_value(row)) if row else False
 
     async def upsert(self, table: str, values: Dict[str, Any], conflict: Sequence[str]) -> int:
         """INSERT ... ON DUPLICATE KEY UPDATE — insert or update on unique/pk clash
 
         `conflict` is the list of columns forming the unique/pk constraint. mysql upserts
         on ANY unique-key clash (it does not name the constraint the way postgres does), so
-        `conflict` is accepted for a call-signature identical to psql but the constraint is
-        whatever unique/pk key the row violates. the wrapper emits ON DUPLICATE KEY UPDATE
-        (psql emits ON CONFLICT for the identical call). returns the affected rowcount.
+        `conflict` is accepted for call-signature parity with psql but the constraint is
+        whatever unique/pk key the row violates. returns the affected rowcount. emits the
+        `col = VALUES(col)` update form, deprecated since MySQL 8.0.20 (warning 1287, still
+        functional) and unaffected on MariaDB; a future MySQL-only build could probe
+        `SELECT VERSION()` and switch to alias syntax, not done here as a documented cost/
+        benefit call, not an oversight.
         """
         cols = list(values.keys())
         placeholders = ", ".join(["%s"] * len(cols))
@@ -392,9 +420,8 @@ class _Transaction:
         try:
             await self._conn.begin()
         except BaseException:
-            # begin() failing after acquire would otherwise leak the pooled connection —
-            # __aexit__ is not called when __aenter__ raises. release it and reset so a
-            # failed transaction start never burns a pool slot.
+            # __aexit__ never runs if __aenter__ raises, so begin() failing after acquire
+            # would otherwise leak the pooled connection — release it here instead.
             await self._pool.release(self._conn)
             self._conn = None
             raise
@@ -407,10 +434,8 @@ class _Transaction:
             else:
                 await self._conn.rollback()
         finally:
-            # aiomysql's release() returns a task (it schedules a _wakeup); await it so we
-            # don't leave an un-awaited task each transaction — matches psql's awaited
-            # release and aiomysql's own idiom. the connection is returned synchronously
-            # inside release() regardless, so pool accounting is never at risk.
+            # release() returns a task (schedules a _wakeup); await it to avoid leaving
+            # it un-awaited each transaction, matching psql's and aiomysql's own idiom.
             await self._pool.release(self._conn)