SpatiaLite Tutorial

GeoAlchemy 2’s main target is PostGIS. But GeoAlchemy 2 also supports SpatiaLite, the spatial extension to SQLite. This tutorial describes how to use GeoAlchemy 2 with SpatiaLite. It’s based on the ORM Tutorial, which you may want to read first.

Connect to the DB

Just like when using PostGIS connecting to a SpatiaLite database requires an Engine. This is how you create one for SpatiaLite:

>>> from sqlalchemy import create_engine
>>> from sqlalchemy.event import listen
>>> def load_spatialite(dbapi_conn, connection_record):
...     dbapi_conn.enable_load_extension(True)
...     dbapi_conn.load_extension('/usr/lib/x86_64-linux-gnu/')
>>> engine = create_engine('sqlite:///gis.db', echo=True)
>>> listen(engine, 'connect', load_spatialite)

The call to create_engine creates an engine bound to the database file gis.db. After that a connect listener is registered on the engine. The listener is responsible for loading the SpatiaLite extension, which is a necessary operation for using SpatiaLite through SQL.

At this point you can test that you are able to connect to the database:

>> conn = engine.connect()
2018-05-30 17:12:02,675 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS VARCHAR(60)) AS anon_1
2018-05-30 17:12:02,676 INFO sqlalchemy.engine.base.Engine ()
2018-05-30 17:12:02,676 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS VARCHAR(60)) AS anon_1
2018-05-30 17:12:02,676 INFO sqlalchemy.engine.base.Engine ()

You can also check that the gis.db SQLite database file was created on the file system.

One additional step is required for using SpatiaLite: create the geometry_columns and spatial_ref_sys metadata tables. This is done by calling SpatiaLite’s InitSpatialMetaData function:

>>> from sqlalchemy.sql import select, func
>>> conn.execute(select([func.InitSpatialMetaData()]))

Note that this operation may take some time the first time it is executed for a database. When InitSpatialMetaData is executed again it will report an error:

InitSpatiaMetaData() error:"table spatial_ref_sys already exists"

You can safely ignore that error.

Before going further we can close the current connection:

>>> conn.close()

Declare a Mapping

Now that we have a working connection we can go ahead and create a mapping between a Python class and a database table.

>>> from sqlalchemy.ext.declarative import declarative_base
>>> from sqlalchemy import Column, Integer, String
>>> from geoalchemy2 import Geometry
>>> Base = declarative_base()
>>> class Lake(Base):
...     __tablename__ = 'lake'
...     id = Column(Integer, primary_key=True)
...     name = Column(String)
...     geom = Column(Geometry(geometry_type='POLYGON', management=True))

This basically works in the way as with PostGIS. The difference is the management argument that must be set to True.

Setting management to True indicates that the AddGeometryColumn and DiscardGeometryColumn management functions will be used for the creation and removal of the geometry column. This is required with SpatiaLite.

Create the Table in the Database

We can now create the lake table in the gis.db database:

>>> Lake.__table__.create(engine)

If we wanted to drop the table we’d use:

>>> Lake.__table__.drop(engine)

There’s nothing specific to SpatiaLite here.

Create a Session

When using the SQLAlchemy ORM the ORM interacts with the database through a Session.

>>> from sqlalchemy.orm import sessionmaker
>>> Session = sessionmaker(bind=engine)
>>> session = Session()

The session is associated with our SpatiaLite Engine. Again, there’s nothing specific to SpatiaLite here.

Add New Objects

We can now create and insert new Lake objects into the database, the same way we’d do it using GeoAlchemy 2 with PostGIS.

>>> lake = Lake(name='Majeur', geom='POLYGON((0 0,1 0,1 1,0 1,0 0))')
>>> session.add(lake)
>>> session.commit()

We can now query the database for Majeur:

>>> our_lake = session.query(Lake).filter_by(name='Majeur').first()
>>> our_lake.geom
<WKBElement at 0x9af594c; '0103000000010000000500000000000000000000000000000000000000000000000000f03f0000000000000000000000000000f03f000000000000f03f0000000000000000000000000000f03f00000000000000000000000000000000'>

Let’s add more lakes:

>>> session.add_all([
...     Lake(name='Garde', geom='POLYGON((1 0,3 0,3 2,1 2,1 0))'),
...     Lake(name='Orta', geom='POLYGON((3 0,6 0,6 3,3 3,3 0))')
... ])
>>> session.commit()


Let’s make a simple, non-spatial, query:

>>> query = session.query(Lake).order_by(
>>> for lake in query:
...     print(

Now a spatial query:

>>> from geolachemy2 import WKTElement
>>> query = session.query(Lake).filter(
...             func.ST_Contains(Lake.geom, WKTElement('POINT(4 1)')))
>>> for lake in query:
...     print(

Here’s another spatial query, using ST_Intersects this time:

>>> query = session.query(Lake).filter(
...             Lake.geom.ST_Intersects(WKTElement('LINESTRING(2 1,4 1)')))
>>> for lake in query:
...     print(

We can also apply relationship functions to geoalchemy2.elements.WKBElement. For example:

>>> lake = session.query(Lake).filter_by(name='Garde').one()
>>> print(session.scalar(lake.geom.ST_Intersects(WKTElement('LINESTRING(2 1,4 1)'))))

session.scalar allows executing a clause and returning a scalar value (an integer value in this case).

The value 1 indicates that the lake “Garde” does intersects the LINESTRING(2 1,4 1) geometry. See the SpatiaLite SQL functions reference list for more information.

Function mapping

Several functions have different names in SpatiaLite than in PostGIS. The GeoAlchemy 2 package is based on the PostGIS syntax but it is possible to automatically translate the queries into SpatiaLite ones. For example, the function ST_GeomFromEWKT is automatically translated into GeomFromEWKT. Unfortunately, only a few functions are automatically mapped (the ones internally used by GeoAlchemy 2). Nevertheless, it is possible to define new mappings in order to translate the queries automatically. Here is an example to register a mapping for the ST_Buffer function:

>>> geoalchemy2.functions.register_sqlite_mapping(
...     {'ST_Buffer': 'Buffer'}
... )

After this command, all ST_Buffer calls in the queries will be translated to Buffer calls when the query is executed on a SQLite DB.

A more complex example is provided for when the PostGIS function should be mapped depending on the given parameters. For example, the ST_Buffer function can actually be translate into either the Buffer function or the SingleSidedBuffer function (only when side=right or side=left is passed). See the Function translation for specific dialect example in the gallery.

Further Reference