MySQL2 Spatial ActiveRecord Adapter
The MySQL2 Spatial ActiveRecord Adapter is an ActiveRecord connection adapter based on the standard mysql2 adapter. It extends the standard adapter to provide support for spatial columns and indexes in MySQL, using the RGeo library to represent spatial data in Ruby. Like the standard mysql2 adapter, this adapter requires the mysql2 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. Remember that, on some versions of MySQL, only the MyISAM engine supports spatial indexes, and the indexed column may need to be NOT NULL.
create_table :my_spatial_table, :options => 'ENGINE=MyISAM' do |t| t.column :latlon, :point, :null => false 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 options, which will be provided based on the SRID embedded in the value itself, since MySQL does not support SRID or dimension constraints on spatial columns themselves. 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.
MySQL server 5.0 or later required for spatial extensions.
ActiveRecord 3.0.3 or later. Earlier versions will not work. Should be compatible with Rails versions through 3.2.x.
mysql2 gem 0.2.13 or later.
rgeo gem 0.3.4 or later.
rgeo-activerecord gem 0.4.3 or later.
Install this adapter as a gem:
gem install activerecord-mysql2spatial-adapter
See the README for the “rgeo” gem, a required dependency, for further installation information.
To use this adapter, add this gem, “activerecord-mysql2spatial-adapter”, to your Gemfile, and then request the adapter name “mysql2spatial” 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 mysql2 adapter, so you can create a new Rails application using:
rails new my_app --database=mysql
…and then just change the adapter name to “mysql2spatial”.
Known bugs and limitations
This adapter is not yet well tested. There are probably some bugs and holes in the functionality. We aren't using MySQL spatial extensions in production at GeoPage, so we would appreciate testing help and feedback from anyone who is.
One known issue is that if you want to use Rails's testing rake tasks and you have spatial indexes in your schema, you should use the :sql dump style. e.g. set config.active_record.schema_format = :sql. The reason is that Rails's Ruby-format schema dumper does not preserve the :options used to create the table, specifically setting the Engine=MyISAM. Under MySQL Spatial, you may create spatial indexes only on MyISAM tables; unfortunately, if you use the Ruby-format schema to create your test databases, Rails does not transfer this information properly, and your test tables are created as InnoDB. The workaround is to use the :sql dump format. This has been reported as a bug in Rails as of Rails 3.0.3, so we hope it will get rectified at some point.
Development and support
Documentation is available at virtuoso.rubyforge.org/activerecord-mysql2spatial-adapter/README_rdoc.html
Source code is hosted on Github at github.com/dazuma/activerecord-mysql2spatial-adapter
Contributions are welcome. Fork the project on Github.
Report bugs on Github issues at github.org/dazuma/activerecord-mysql2spatial-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 Mysql2Spatial Adapter and its supporting libraries (including RGeo) are written by Daniel Azuma (www.daniel-azuma.com).
Development is supported by Pirq. (www.pirq.com).
This adapter implementation owes some debt to the spatial_adapter plugin (github.com/fragility/spatial_adapter). Although we made a few different design decisions for this adapter, studying the spatial_adapter source gave us a head start on the implementation.
Copyright 2010-2011 Daniel Azuma
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