implement actual database searches

nominatim/api/connection.py

@@ -7,11 +7,13 @@
 """
 Extended SQLAlchemy connection class that also includes access to the schema.
 """
-from typing import Any, Mapping, Sequence, Union, Dict, cast
+from typing import cast, Any, Mapping, Sequence, Union, Dict, Optional, Set
 
 import sqlalchemy as sa
+from geoalchemy2 import Geometry
 from sqlalchemy.ext.asyncio import AsyncConnection
 
+from nominatim.typing import SaFromClause
 from nominatim.db.sqlalchemy_schema import SearchTables
 from nominatim.api.logging import log
 
@@ -28,6 +30,7 @@ class SearchConnection:
         self.connection = conn
         self.t = tables # pylint: disable=invalid-name
         self._property_cache = properties
+        self._classtables: Optional[Set[str]] = None
 
 
     async def scalar(self, sql: sa.sql.base.Executable,
@@ -87,3 +90,26 @@ class SearchConnection:
             raise ValueError(f"DB setting '{name}' not found in database.")
 
         return self._property_cache['DB:server_version']
+
+
+    async def get_class_table(self, cls: str, typ: str) -> Optional[SaFromClause]:
+        """ Lookup up if there is a classtype table for the given category
+            and return a SQLAlchemy table for it, if it exists.
+        """
+        if self._classtables is None:
+            res = await self.execute(sa.text("""SELECT tablename FROM pg_tables
+                                                WHERE tablename LIKE 'place_classtype_%'
+                                             """))
+            self._classtables = {r[0] for r in res}
+
+        tablename = f"place_classtype_{cls}_{typ}"
+
+        if tablename not in self._classtables:
+            return None
+
+        if tablename in self.t.meta.tables:
+            return self.t.meta.tables[tablename]
+
+        return sa.Table(tablename, self.t.meta,
+                        sa.Column('place_id', sa.BigInteger),
+                        sa.Column('centroid', Geometry(srid=4326, spatial_index=False)))