Added postgresql database

This adds a postgresql database to the program. It also includes CI testing for the postgresql database (maybe interesting for you, @marius, or you have a comment).

\approve @prehn

obmdataapi/__init__.py

@@ -18,9 +18,13 @@
 
 import logging
 import sys
+import os
 
-from quart import Quart
 from ajsonrpc.backend.quart import JSONRPCQuart
+from databases import Database
+from dotenv import load_dotenv
+from pathlib import Path
+from quart import Quart
 
 logger = logging.getLogger()
 logger.setLevel(logging.DEBUG)
@@ -28,14 +32,55 @@ logger.addHandler(logging.StreamHandler(sys.stdout))
 
 logger.info("obmapidata has started")
 
+load_dotenv(Path(".env").resolve())
+
 app = Quart(__name__)
 app.api = JSONRPCQuart()
 
+
+# Load configuration from file
+config_file = Path("config.py")
+if config_file.is_file():
+    app.config.from_pyfile(config_file.resolve())
+
+# Allow some environment variables to overrite configuration
+if "OBM_DATA_API_DATABASE_URL" in os.environ:
+    app.config.update(DATABASE_URL=os.environ.get("OBM_DATA_API_DATABASE_URL"))
+if "OBM_DATA_API_TESTING" in os.environ:
+    app.config.update(TESTING=os.environ.get("OBM_DATA_API_TESTING"))
+
+
+# Define main entrypoint for JSON-RPC API
 app.post(
     "/v1",
 )(app.api.handler)
 
+# Add database connection
+@app.before_serving
+async def startup() -> None:
+    app.db = await _create_database_connection()
+
+
+async def _create_database_connection() -> Database:
+    db = Database(
+        app.config.get("DATABASE_URL", "postgresql://postgres:@localhost:5432/dataapi")
+    )
+    await db.connect()
+    return db
+
+
+# JSON-RPC API endpoints
+
 
 @app.api.add_function
 async def heartbeat() -> dict:
     return {"status": "healthy"}
+
+
+@app.api.add_function
+async def get_building(osm_id) -> dict:
+    building = await app.db.fetch_val(
+        "SELECT osm_id FROM osm_building_polygons WHERE osm_id = :osm_id",
+        values={"osm_id": int(osm_id)},
+    )
+    return {"building": str(building)}