Spatial Adapter for ActiveRecord

This is the Spatial Adapter for ActiveRecord. It enhances ActiveRecord to handle spatial datatypes in the following databases:

  • PostgreSQL (using PostGIS)

  • MySQL (using Spatial Extensions)

Dependencies

The following gems are required:

  • GeoRuby

  • ActiveRecord (version 2.2.2 and up)

For PostgreSQL:

  • PostGIS version 1.4.0 or higher should be installed in your database

Installation

Choose ONE of the following installation methods. You shouldn’t have to do both.

From RubyGems

This is the preferred method of installation, and will pull in the required dependencies as well.

gem install spatial_adapter

In a Rails app, you can add a gem dependency in environment.rb:

config.gem "spatial_adapter"

As a Rails Plugin

In your Rails project, run the following:

script/plugin install git://github.com/fragility/spatial_adapter.git

You need to have Git installed first.

Configuration

Choose the database type for which you would like to use spatial_adapter, and load each with

require 'spatial_adapter/[database]'

where [database] should be replaced with one of the following:

  • postgresql

  • mysql

For example to use the PostgreSQL spatial adapter:

require 'spatial_adapter/postgresql'

In a Rails app, spatial_adapter will automatically load the adapter for the database specified in your database.yml configuration.

Operations

Geometric columns in your ActiveRecord models now appear just like any other column of other basic data types. They can also be dumped in ruby schema mode and loaded in migrations the same way as columns of basic types.

Migrations

Here is an example of code for the creation of a table with a geometric column in PostGIS, along with the addition of a spatial index on the column:

ActiveRecord::Schema.define do
  create_table :table_points, :force => true do |t|
    t.string :data
    t.point :geom, :null => false, :srid => 123, :with_z => true
  end
  add_index :table_points, :geom, :spatial => true
end

Here is a related statement valid for MySql version <= 5.0.16:

ActiveRecord::Schema.define do
  create_table "table_points", ;options=>"ENGINE=MyISAM", :force => true do |t|
    t.string :data
    t.point :geom, :null => false
  end
  add_index :table_points, :geom, :spatial => true
end

Differences Between Databases

  • On all versions of MySQL, the :srid, :with_z, and :with_m options are ignored, since they are not supported.

  • On MySQL versions <= 5.0.16, you have to add :options => "ENGINE=MyISAM" to the create_table statement, since only MyISAM tables can have spatial columns. In addition, only MyISAM tables may have spatial indexes.

Models

Create your ActiveRecord models normally. Spatial Adapter will automatically handle spatial columns, converting them to the appropriate GeoRuby type.

class TablePoint < ActiveRecord::Base
end

Access

Here is an example of row creation and access, using the model and the table defined above:

pt = TablePoint.new(
  :data => "Hello!", 
  :geom => Point.from_x_y_z(-1.6, 2.8, -3.4, 123))
pt.save
pt = TablePoint.find_first
puts pt.geom.x #access the geom column like any other

Fixtures

If you use fixtures for your unit tests, at some point, you will want to input a geometry. You could transform your geometries to a form suitable for YAML yourself every time but Spatial Adapter provides a method to do it for you: to_fixture_format. You would use it like this, if the geometric column is a point:

fixture:
  id: 1
  data: HELLO
  geom: <%= Point.from_x_y(123.5,321.9).to_fixture_format %>

Finder Enhancements

Enhancements to find_by_* and friends has been removed from this version of Spatial Adapter until a cleaner implementation can be made. (The previous implementation made adapter-specific modifications to ActiveRecord::Base, which prevented multiple adapters from being loaded at once.)

Geometric data types

Ruby geometric datatypes are currently made available only through the GeoRuby library (georuby.rubyforge.org/): This is where the Point.from_x_y in the example above comes from.

Warning

  • Since ActiveRecord seems to keep only the string values directly returned from the database, it translates from these to the correct types everytime an attribute is read, which is probably ok for simple types, but might be less than efficient for geometries, since the EWKB string has to be parsed everytime. Also it means you cannot modify the geometry object returned from an attribute directly:

    place = Place.find_first
place.the_geom.y=123456.7 # this doesn't work

    Since the translation to a geometry is performed every time the_geom is read, the change to y will not be saved! You would have to do something like this:

    place = Place.find_first
the_geom = place.the_geom
the_geom.y=123456.7
place.the_geom = the_geom

License

The Spatial Adapter for ActiveRecord is released under the MIT license.

Latest Changes

Spatial Adapter has been refactored and is now available as a Ruby gem. The dependency on Rails has been removed. Unfortunately, the current version is without some of the previous functionality, until a cleaner implementation is made.

The previous release is available on the “legacy” branch.

Removed Features in 0.2.0

  • Compatibility with ActiveRecord/Rails older than version 2.2.2

  • enhancements to find_by_* for spatial columns

  • to_fixture_format extension to the GeoRuby types

These will hopefully be added back in the near future.

Support

Any questions, enhancement proposals, bug notifications or corrections can be made via the project page at github.com/fragility/spatial_adapter