feat: migrate database driver from MariaDB to PostgreSQL

Switch from pymysql to psycopg2-binary, update connection string to
postgresql+psycopg2, replace MySQL-specific JSON imports with generic
SQLAlchemy JSON, convert MySQL prefix index to PostgreSQL left() function,
and remove FetchedValue() (unnecessary with PostgreSQL).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/.env.example

@@ -1,6 +1,6 @@
 # Database
 DB_HOST=
-DB_PORT=3306
+DB_PORT=5432
 DB_NAME=dak_c2s
 DB_USER=dak_c2s_admin
 DB_PASSWORD=

backend/app/config.py

@@ -8,7 +8,7 @@ from functools import lru_cache
 class Settings(BaseSettings):
     # Database
     DB_HOST: str = "localhost"
-    DB_PORT: int = 3306
+    DB_PORT: int = 5432
     DB_NAME: str = "dak_c2s"
     DB_USER: str = "dak_c2s_admin"
     DB_PASSWORD: str = ""
@@ -37,8 +37,8 @@ class Settings(BaseSettings):
     def database_url(self) -> str:
         password = quote_plus(self.DB_PASSWORD)
         return (
-            f"mysql+pymysql://{self.DB_USER}:{password}"
+            f"postgresql+psycopg2://{self.DB_USER}:{password}"
-            f"@{self.DB_HOST}:{self.DB_PORT}/{self.DB_NAME}?charset=utf8mb4"
+            f"@{self.DB_HOST}:{self.DB_PORT}/{self.DB_NAME}"
         )
 
     class Config:

backend/app/models/audit.py

@@ -12,11 +12,11 @@ from sqlalchemy import (
     ForeignKey,
     Index,
     Integer,
+    JSON,
     String,
     Text,
     func,
 )
-from sqlalchemy.dialects.mysql import JSON
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base

backend/app/models/case.py

@@ -21,7 +21,6 @@ from sqlalchemy import (
     text,
 )
 from sqlalchemy.orm import Mapped, mapped_column, relationship
-from sqlalchemy.schema import FetchedValue
 
 from app.database import Base
 
@@ -115,7 +114,6 @@ class Case(Base):
         nullable=False,
         server_default=func.now(),
         onupdate=func.now(),
-        server_onupdate=FetchedValue(),
     )
     updated_by: Mapped[Optional[int]] = mapped_column(
         Integer, ForeignKey("users.id"), nullable=True
@@ -154,9 +152,9 @@ class Case(Base):
         Index("idx_fallgruppe", "fallgruppe"),
         Index("idx_datum", "datum"),
         Index("idx_nachname_vorname", "nachname", "vorname"),
-        # Note: idx_pending_icd uses a prefix length icd(20) which SQLAlchemy
+        # Note: idx_pending_icd uses a functional index on left(icd, 20).
-        # does not support natively. We use text() for the prefix column.
+        # We use text() for the expression column.
-        Index("idx_pending_icd", "jahr", "kw", "fallgruppe", text("icd(20)")),
+        Index("idx_pending_icd", "jahr", "kw", "fallgruppe", text("left(icd, 20)")),
         Index("idx_pending_coding", "gutachten", "gutachten_typ"),
         CheckConstraint(
             "fallgruppe IN ('onko','kardio','intensiv','galle','sd')",

backend/app/models/report.py

@@ -11,12 +11,12 @@ from sqlalchemy import (
     ForeignKey,
     Index,
     Integer,
+    JSON,
     SmallInteger,
     String,
     UniqueConstraint,
     func,
 )
-from sqlalchemy.dialects.mysql import JSON
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from app.database import Base

backend/app/models/user.py

@@ -17,7 +17,6 @@ from sqlalchemy import (
     func,
 )
 from sqlalchemy.orm import Mapped, mapped_column, relationship
-from sqlalchemy.schema import FetchedValue
 
 from app.database import Base
 
@@ -59,7 +58,6 @@ class User(Base):
         nullable=False,
         server_default=func.now(),
         onupdate=func.now(),
-        server_onupdate=FetchedValue(),
     )
 
     # Relationships

backend/requirements.txt

@@ -3,7 +3,7 @@ uvicorn[standard]==0.34.0
 gunicorn==23.0.0
 sqlalchemy==2.0.36
 alembic==1.14.1
-pymysql==1.1.1
+psycopg2-binary==2.9.10
 cryptography==44.0.0
 python-jose[cryptography]==3.3.0
 passlib[bcrypt]==1.7.4

deploy/dak-backend.service

@@ -1,6 +1,6 @@
 [Unit]
 Description=DAK Zweitmeinungs-Portal Backend (FastAPI/Uvicorn)
-After=network.target mariadb.service
+After=network.target postgresql.service
 
 [Service]
 Type=simple