add exporting of SQLite table

nominatim/tools/convert_sqlite.py

@@ -8,12 +8,17 @@
 Exporting a Nominatim database to SQlite.
 """
 from typing import Set
+import logging
 from pathlib import Path
 
 import sqlalchemy as sa
 
+from nominatim.typing import SaSelect
+from nominatim.db.sqlalchemy_types import Geometry
 import nominatim.api as napi
 
+LOG = logging.getLogger()
+
 async def convert(project_dir: Path, outfile: Path, options: Set[str]) -> None:
     """ Export an existing database to sqlite. The resulting database
         will be usable against the Python frontend of Nominatim.
@@ -24,7 +29,115 @@ async def convert(project_dir: Path, outfile: Path, options: Set[str]) -> None:
         outapi = napi.NominatimAPIAsync(project_dir,
                                         {'NOMINATIM_DATABASE_DSN': f"sqlite:dbname={outfile}"})
 
-        async with api.begin() as inconn, outapi.begin() as outconn:
-            pass
+        async with api.begin() as src, outapi.begin() as dest:
+            writer = SqliteWriter(src, dest, options)
+            await writer.write()
     finally:
         await api.close()
+
+
+class SqliteWriter:
+    """ Worker class which creates a new SQLite database.
+    """
+
+    def __init__(self, src: napi.SearchConnection,
+                 dest: napi.SearchConnection, options: Set[str]) -> None:
+        self.src = src
+        self.dest = dest
+        self.options = options
+
+
+    async def write(self) -> None:
+        """ Create the database structure and copy the data from
+            the source database to the destination.
+        """
+        await self.dest.execute(sa.select(sa.func.InitSpatialMetaData(True, 'WGS84')))
+
+        await self.create_tables()
+        await self.copy_data()
+        await self.create_indexes()
+
+
+    async def create_tables(self) -> None:
+        """ Set up the database tables.
+        """
+        if 'search' not in self.options:
+            self.dest.t.meta.remove(self.dest.t.search_name)
+
+        await self.dest.connection.run_sync(self.dest.t.meta.create_all)
+
+        # Convert all Geometry columns to Spatialite geometries
+        for table in self.dest.t.meta.sorted_tables:
+            for col in table.c:
+                if isinstance(col.type, Geometry):
+                    await self.dest.execute(sa.select(
+                        sa.func.RecoverGeometryColumn(table.name, col.name, 4326,
+                                                      col.type.subtype.upper(), 'XY')))
+
+
+    async def copy_data(self) -> None:
+        """ Copy data for all registered tables.
+        """
+        for table in self.dest.t.meta.sorted_tables:
+            LOG.warning("Copying '%s'", table.name)
+            async_result = await self.src.connection.stream(self.select_from(table.name))
+
+            async for partition in async_result.partitions(10000):
+                data = [{('class_' if k == 'class' else k): getattr(r, k) for k in r._fields}
+                        for r in partition]
+                await self.dest.execute(table.insert(), data)
+
+
+    async def create_indexes(self) -> None:
+        """ Add indexes necessary for the frontend.
+        """
+        # reverse place node lookup needs an extra table to simulate a
+        # partial index with adaptive buffering.
+        await self.dest.execute(sa.text(
+            """ CREATE TABLE placex_place_node_areas AS
+                  SELECT place_id, ST_Expand(geometry,
+                                             14.0 * exp(-0.2 * rank_search) - 0.03) as geometry
+                  FROM placex
+                  WHERE rank_address between 5 and 25
+                        and osm_type = 'N'
+                        and linked_place_id is NULL """))
+        await self.dest.execute(sa.select(
+            sa.func.RecoverGeometryColumn('placex_place_node_areas', 'geometry',
+                                          4326, 'GEOMETRY', 'XY')))
+        await self.dest.execute(sa.select(sa.func.CreateSpatialIndex(
+                                             'placex_place_node_areas', 'geometry')))
+
+        # Remaining indexes.
+        await self.create_spatial_index('country_grid', 'geometry')
+        await self.create_spatial_index('placex', 'geometry')
+        await self.create_spatial_index('osmline', 'linegeo')
+        await self.create_spatial_index('tiger', 'linegeo')
+        await self.create_index('placex', 'place_id')
+        await self.create_index('placex', 'rank_address')
+        await self.create_index('addressline', 'place_id')
+
+
+    async def create_spatial_index(self, table: str, column: str) -> None:
+        """ Create a spatial index on the given table and column.
+        """
+        await self.dest.execute(sa.select(
+                  sa.func.CreateSpatialIndex(getattr(self.dest.t, table).name, column)))
+
+
+    async def create_index(self, table_name: str, column: str) -> None:
+        """ Create a simple index on the given table and column.
+        """
+        table = getattr(self.dest.t, table_name)
+        await self.dest.connection.run_sync(
+            sa.Index(f"idx_{table}_{column}", getattr(table.c, column)).create)
+
+
+    def select_from(self, table: str) -> SaSelect:
+        """ Create the SQL statement to select the source columns and rows.
+        """
+        columns = self.src.t.meta.tables[table].c
+
+        sql = sa.select(*(sa.func.ST_AsText(c).label(c.name)
+                             if isinstance(c.type, Geometry) else c for c in columns))
+
+        return sql