SpatiaLite ActiveRecord Adapter
The SpatiaLite ActiveRecord Adapter is an ActiveRecord connection adapter based on the standard sqlite3 adapter. It extends the standard adapter to provide support for spatial extensions using SpatiaLite, using the RGeo library to represent spatial data in Ruby. Like the standard sqlite3 adapter, this adapter requires the sqlite3-ruby gem.
What This Adapter Provides
First, this adapter extends the migration syntax to support creating spatial columns and indexes. To create a spatial column, use the :geometry type, or any of the OGC spatial types such as :point or :line_string. To create a spatial index, set the :spatial option to true.
create_table :my_spatial_table do |t| t.column :latlon, :point # or t.point :latlon t.line_string :path t.geometry :shape end change_table :my_spatial_table do |t| t.index :latlon, :spatial => true end
When this adapter is in use, spatial attributes in your ActiveRecord objects will have RGeo geometry values. You can set spatial attributes either to RGeo geometry objects, or to strings in WKT (well-known text) format, which the adapter will automatically convert to geometry objects.
Spatial objects in RGeo are tied to a factory that specifies the coordinate system as well as other behaviors of the object. You must therefore specify a factory for each spatial column (attribute) in your ActiveRecord class. You can either set an explicit factory for a specific column, or provide a factory generator that will yield the appropriate factory for the table's spatial columns based on their types. For the former, call the set_rgeo_factory_for_column class method on your ActiveRecord class. For the latter, set the rgeo_factory_generator class attribute. This generator should understand at least the :srid option, which will be provided based on the column's specified SRID. Note that the spatialite adapter does not currently support Z or M coordinates, as it's unclear to me whether SpatiaLite itself supports them. The set_rgeo_factory_for_column and rgeo_factory_generator methods are actually implemented and documented in the “rgeo-activerecord” gem.
Examples, given the spatial table defined above:
class MySpatialTable < ActiveRecord::Base # By default, use the GEOS implementation for spatial columns. self.rgeo_factory_generator = RGeo::Geos.method(:factory) # But use a geographic implementation for the :latlon column. set_rgeo_factory_for_column(:latlon, RGeo::Geographic.spherical_factory) end
Now you can interact with the data using the RGeo types:
rec = MySpatialTable.new rec.latlon = 'POINT(-122 47)' # You can set by feature object or WKT. loc = rec.latlon # Accessing always returns a feature object, in # this case, a geographic that understands latitude. loc.latitude # => 47 rec.shape = loc # the factory for the :shape column is GEOS, so the # value will be cast from geographic to GEOS. RGeo::Geos.is_geos?(rec.shape) # => true
You can create simple queries based on objective equality in the same way you would on a scalar column:
rec = MySpatialTable.where(:latlon => RGeo::Geos.factory.point(-122, 47)).first
You can also use WKT:
rec = MySpatialTable.where(:latlon => 'POINT(-122 47)').first
The adapter also provides experimental support for more complex queries such as radius searches. However, these extensions require Arel 2.1 (which is scheduled for release with Rails 3.1). We do not have these documented yet, and the syntax is subject to change. For now, you should write more complex queries in SQL.
Installation And Configuration
Installing The Adapter Gem
This adapter has the following requirements:
Ruby 1.8.7 or later. Ruby 1.9.2 or later preferred.
sqlite 3.7.3 or later.
SpatiaLite 3.0 or later. Version 2.3 may work but is not officially supported.
sqlite3 gem 1.3.5 or later.
ActiveRecord 3.0.3 or later. Earlier versions will not work. Should be compatible with Rails versions through 3.2.x.
rgeo gem 0.3.7 or later.
rgeo-activerecord gem 0.4.3 or later.
Note: if you are running Mac OS X, the OS-provided copy of sqlite3 may not support extensions. You should install an alternate copy of sqlite3 (for example, using MacPorts or Homebrew) reinstall the gem using:
gem install sqlite3 -- --with-sqlite3-dir=/path/to/alternate/sqlite3
Install this adapter as a gem:
gem install activerecord-spatialite-adapter
See the README for the “rgeo” gem, a required dependency, for further installation information.
Setting Up The Adapter
To use this adapter, add this gem, “activerecord-spatialite-adapter”, to your Gemfile, and then request the adapter name “spatialite” in your database connection configuration (which, for a Rails application, is in the config/database.yml file). The other database connection configuration parameters are the same as for the stock sqlite3 adapter, with the exception of one additional parameter, libspatialite, which should be set to the full path to the libspatialite shared library, if it is not installed in a standard place (such as /usr/local or /opt/local).
Generally, you can create a new Rails application using:
rails new my_app --database=sqlite3
…and then change the adapter names to “spatialite” and add an appropriate libspatialite setting.
Next, the SpatiaLite adapter includes a special railtie that provides support for SpatiaLite databases in ActiveRecord's rake tasks. This railtie is required in order to run, e.g., rake test. To install this railtie, you should add this line to your config/application.rb:
Note that this railtie must load after the ActiveRecord railtie. That is, the above require command should appear after require 'rails/all'.
Dealing with SpatiaLite Definitions
SpatiaLite adds many objects (meta-information tables, functions, triggers, etc.) to a Sqlite3 database. These objects are required to maintain the spatial elements of the database, but they can be a hassle when managing the database with Rails. Following are some tips and gotchas that you may encounter.
Make sure you include the correct libspatialite setting in your database.yml config file, especially for your production environments.
SpatiaLite databases need to be initialized by executing the SpatiaLite initialization script or by calling the InitSpatialMetaData() function. The rake db:create task will do this for you when it creates a database. Thus, when setting up a new application, you should make sure you call rake db:create or otherwise cause the SpatiaLite initialization to occur, before you attempt to run your first migration. Failure to do so will result in errors during the migration.
Dumping a SpatiaLite database as SQL will cause a bunch of internal tables and triggers to be included in your dump. These are the actual SpatiaLite implementation objects used to enforce spatial constraints and implement spatial indexes. Unfortunately, not only is this a bit unsightly, but not everything is dumped here: for example, for each spatial column, there should be a row in the geometry_columns table, and those will be missing in the SQL structure dump. As a result, loading from the SQL structure dump will not properly reproduce your database schema. Because of this, we highly recommend that you leave config.active_record.schema_format set to :ruby for now, so that schema dumps are done in the Ruby format.
Known bugs and limitations
The spatialite adapter works in principle, but there are a few known holes in the functionality. Notably, things that require the alter_table mechanism may not function properly, because the current sqlite3 implementation doesn't properly preserve triggers. This means, among other things, removing columns in tables with spatial information can cause the remaining spatial columns to fail. However, most simple things work, including creating tables with geometric columns, adding geometric columns to existing tables, and creating and removing spatial R*tree indexes. Note that this adapter is not yet well tested.
Development and support
Documentation is available at dazuma.github.com/activerecord-spatialite-adapter/rdoc
Source code is hosted on Github at github.com/dazuma/activerecord-spatialite-adapter
Contributions are welcome. Fork the project on Github.
Report bugs on Github issues at github.org/dazuma/activerecord-spatialite-adapter/issues
Support available on the rgeo-users google group at groups.google.com/group/rgeo-users
Contact the author at dazuma at gmail dot com.
The SpatiaLite Adapter and its supporting libraries (including RGeo) are written by Daniel Azuma (www.daniel-azuma.com).
Development is supported by Pirq. (www.pirq.com).
Copyright 2010-2012 Daniel Azuma
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