Remove PEP-249 exception mirror — use psycopg exceptions directly

Plain mirrored psycopg's entire PEP-249 exception hierarchy and used
DatabaseErrorWrapper to catch every psycopg exception and re-raise it
as a Plain equivalent. This was a Django pattern for multi-DB
abstraction that served no purpose in a PostgreSQL-only framework.

Now psycopg exceptions propagate unchanged. User code catches
psycopg.IntegrityError, psycopg.errors.UniqueViolation, etc. directly,
giving access to richer subclasses and diagnostic fields that the
mirror obscured.

DatabaseErrorWrapper is simplified to only track connection health
(errors_occurred flag) without converting exception types.

Author: davegaeddert

plain-cache/plain/cache/core.py

@@ -4,6 +4,7 @@
 from functools import cached_property
 from typing import Any
 
+import psycopg
 from opentelemetry import trace
 from opentelemetry.semconv.attributes.db_attributes import (
     DB_NAMESPACE,
@@ -12,7 +13,6 @@
 )
 from opentelemetry.trace import SpanKind
 
-from plain.postgres import IntegrityError
 from plain.utils import timezone
 
 tracer = trace.get_tracer("plain.cache")
@@ -137,7 +137,7 @@ def set(
                 item, _ = self._model_class.query.update_or_create(
                     key=self.key, defaults=defaults
                 )
-            except IntegrityError:
+            except psycopg.IntegrityError:
                 # Most likely a race condition in creating the item,
                 # so trying again should do an update
                 item, _ = self._model_class.query.update_or_create(

plain-flags/plain/flags/preflight.py

@@ -1,4 +1,5 @@
-from plain.postgres.db import OperationalError, ProgrammingError
+import psycopg
+
 from plain.preflight import PreflightCheck, PreflightResult, register_check
 from plain.runtime import settings
 
@@ -25,7 +26,7 @@ def run(self) -> list[PreflightResult]:
 
         try:
             flag_names = set(flag_names)
-        except (ProgrammingError, OperationalError):
+        except (psycopg.ProgrammingError, psycopg.OperationalError):
             # The table doesn't exist yet
             # (migrations probably haven't run yet),
             # so we can't check it.

plain-oauth/plain/oauth/models.py

@@ -3,11 +3,12 @@
 import datetime
 from typing import TYPE_CHECKING, Any
 
+import psycopg
+
 from plain import postgres
 from plain.auth import get_user_model
 from plain.exceptions import ValidationError
 from plain.postgres import transaction, types
-from plain.postgres.db import IntegrityError
 from plain.runtime import SettingsReference
 from plain.utils import timezone
 
@@ -119,7 +120,7 @@ def get_or_create_user(
                             **oauth_user.user_model_fields,
                         )
                         user.save()
-                except (IntegrityError, ValidationError):
+                except (psycopg.IntegrityError, ValidationError):
                     raise OAuthUserAlreadyExistsError(
                         provider_key=provider_key,
                         user_model_fields=oauth_user.user_model_fields,

plain-oauth/plain/oauth/preflight.py

@@ -1,4 +1,5 @@
-from plain.postgres.db import OperationalError, ProgrammingError
+import psycopg
+
 from plain.preflight import PreflightCheck, PreflightResult, register_check
 
 
@@ -18,7 +19,7 @@ def run(self) -> list[PreflightResult]:
             keys_in_db = set(
                 OAuthConnection.query.values_list("provider_key", flat=True).distinct()
             )
-        except (OperationalError, ProgrammingError):
+        except (psycopg.OperationalError, psycopg.ProgrammingError):
             # Check runs on plain migrate, and the table may not exist yet
             # or it may not be installed on the particular database intentionally
             return errors

plain-postgres/plain/postgres/README.md

@@ -403,14 +403,14 @@ with transaction.atomic():
 
 ### Read-only connections
 
-Enforce read-only mode on the current database connection using `read_only()`. Any write (INSERT, UPDATE, DELETE, DDL) raises a [`ReadOnlyError`](./exceptions.py#ReadOnlyError):
+Enforce read-only mode on the current database connection using `read_only()`. Any write (INSERT, UPDATE, DELETE, DDL) raises `psycopg.errors.ReadOnlySqlTransaction`:
 
 ```python
 from plain.postgres.connections import read_only
 
 with read_only():
     users = User.query.all()       # reads work
-    User.query.create(name="x")   # raises ReadOnlyError
+    User.query.create(name="x")   # raises psycopg.errors.ReadOnlySqlTransaction
 ```
 
 This works with both autocommit queries and explicit `atomic()` blocks.

plain-postgres/plain/postgres/__init__.py

@@ -6,7 +6,7 @@
 # Imports that would create circular imports if sorted
 from .base import Model
 from .constraints import CheckConstraint, UniqueConstraint
-from .db import IntegrityError, get_connection
+from .db import get_connection
 from .deletion import CASCADE, DO_NOTHING, PROTECT, RESTRICT, SET, SET_DEFAULT, SET_NULL
 from .enums import IntegerChoices, TextChoices
 from .fields import (
@@ -111,7 +111,6 @@
     "ReverseManyToMany",
     # From db
     "get_connection",
-    "IntegrityError",
     # From registry
     "register_model",
     "models_registry",

plain-postgres/plain/postgres/base.py

@@ -10,15 +10,14 @@
     from plain.postgres.meta import Meta
     from plain.postgres.options import Options
 
+import psycopg
+
 import plain.runtime
 from plain.exceptions import NON_FIELD_ERRORS, ValidationError
 from plain.postgres import models_registry, transaction, types
 from plain.postgres.constants import LOOKUP_SEP
 from plain.postgres.constraints import CheckConstraint, UniqueConstraint
-from plain.postgres.db import (
-    PLAIN_VERSION_PICKLE_KEY,
-    DatabaseError,
-)
+from plain.postgres.db import PLAIN_VERSION_PICKLE_KEY
 from plain.postgres.deletion import Collector
 from plain.postgres.dialect import MAX_NAME_LENGTH
 from plain.postgres.exceptions import (
@@ -496,9 +495,11 @@ def _save_table(
                 base_qs, id_val, values, update_fields, forced_update
             )
             if force_update and not updated:
-                raise DatabaseError("Forced update did not affect any rows.")
+                raise psycopg.DatabaseError("Forced update did not affect any rows.")
             if update_fields and not updated:
-                raise DatabaseError("Save with update_fields did not affect any rows.")
+                raise psycopg.DatabaseError(
+                    "Save with update_fields did not affect any rows."
+                )
         if not updated:
             fields = meta.local_concrete_fields
             if not id_set:

plain-postgres/plain/postgres/cli/db.py

@@ -6,11 +6,12 @@
 from collections import defaultdict
 
 import click
+import psycopg
 
 from plain.cli import register_cli
 
 from ..backups.cli import cli as backups_cli
-from ..db import OperationalError, get_connection
+from ..db import get_connection
 from ..dialect import quote_name
 from ..migrations.recorder import MIGRATION_TABLE_NAME
 
@@ -126,7 +127,7 @@ def wait() -> None:
 
         try:
             get_connection().ensure_connection()
-        except OperationalError:
+        except psycopg.OperationalError:
             waiting_for = True
 
         if waiting_for:

plain-postgres/plain/postgres/db.py

@@ -5,19 +5,7 @@
 from plain import signals
 
 from .connections import get_connection, has_connection
-from .exceptions import (
-    DatabaseError,
-    DatabaseErrorWrapper,
-    DataError,
-    Error,
-    IntegrityError,
-    InterfaceError,
-    InternalError,
-    NotSupportedError,
-    OperationalError,
-    ProgrammingError,
-    ReadOnlyError,
-)
+from .exceptions import DatabaseErrorWrapper
 
 PLAIN_VERSION_PICKLE_KEY = "_plain_version"
 
@@ -46,16 +34,6 @@ def close_old_connections(**kwargs: Any) -> None:
     "get_connection",
     "has_connection",
     "PLAIN_VERSION_PICKLE_KEY",
-    "Error",
-    "InterfaceError",
-    "DatabaseError",
-    "DataError",
-    "OperationalError",
-    "IntegrityError",
-    "InternalError",
-    "ProgrammingError",
-    "NotSupportedError",
     "DatabaseErrorWrapper",
-    "ReadOnlyError",
     "close_old_connections",
 ]

plain-postgres/plain/postgres/deletion.py

@@ -7,11 +7,12 @@
 from operator import attrgetter, or_
 from typing import TYPE_CHECKING, Any
 
+import psycopg
+
 from plain.postgres import (
     query_utils,
     transaction,
 )
-from plain.postgres.db import IntegrityError
 from plain.postgres.meta import Meta
 from plain.postgres.query import QuerySet
 from plain.postgres.sql import DeleteQuery, UpdateQuery
@@ -28,16 +29,16 @@
 _LAZY_ON_DELETE: set[Callable[..., Any]] = set()
 
 
-class ProtectedError(IntegrityError):
+class ProtectedError(psycopg.IntegrityError):
     def __init__(self, msg: str, protected_objects: Iterable[Any]) -> None:
         self.protected_objects = protected_objects
-        super().__init__(msg, protected_objects)
+        super().__init__(msg)
 
 
-class RestrictedError(IntegrityError):
+class RestrictedError(psycopg.IntegrityError):
     def __init__(self, msg: str, restricted_objects: Iterable[Any]) -> None:
         self.restricted_objects = restricted_objects
-        super().__init__(msg, restricted_objects)
+        super().__init__(msg)
 
 
 def CASCADE(collector: Collector, field: RelatedField, sub_objs: Any) -> None: