= 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 your 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.

== 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 <tt>:options =>
  "ENGINE=MyISAM"</tt> 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 (http://georuby.rubyforge.org/): This is where the
<tt>Point.from_x_y</tt> 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 http://github.com/fragility/spatial_adapter