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PostGIS 1.5 Notes

The latest version of activerecord-postgis-adapter requires PostGIS 2.0+. These notes apply only to PostGIS 1.5. If you are using PostGIS 1.5, use version 0.6.x of the adapter and read this section.

Gemfile:

gem 'activerecord-postgis-adapter', '~> 0.6.6'

PostGIS 1.5 Install Notes

database.yml

Creating the PostGIS extension

If you have an older PostgreSQL or an older PostGIS you will not be able to run the SQL command create extension postgis to install PostGIS into your database. In this case, instead of including postgis_extension, you should include script_dir in the database.yml configuration. This should be set to a directory containing two files that contain all the PostGIS-provided spatial definitions: postgis.sql and spatial_ref_sys.sql.

This directory is usually in the share/contrib directory of your PostgreSQL installation. To find it, run

pg_config --sharedir

Then, append contrib, and look for a subdirectory named "postgis-(version)". For example, if you installed PostgreSQL in /usr/local, and you are running PostGIS 1.5, you should probably set script_dir to /usr/local/share/contrib/postgis-1.5.

If you are using a template to install PostGIS into your database then set the template configuration as appropriate, and omit both the postgis_extension and script_dir configurations. In this case, you also do not need to include su_username or su_password, since those configurations apply only to adding the extension or using the script dir.

If you do not want the spatial declarations to live in a separate schema then do not include "postgis" on the schema_search_path. Note that we recommend separating PostGIS into a separate schema, because that is the best way to ensure rake test works properly and is able to create the test database.

schema_search_path

If you include a schema called "postgis" in the search path, the adapter will isolate all the PostGIS-specific definitions, including data types, functions, views, and so forth, into that schema instead of including them in the default "public" schema. Then, when Rails needs to dump the schema (for example, to replicate it for the test database), it can use that isolation to omit the PostGIS definitions from cluttering the schema dump.

The credentials that your app will use to connect to the database should be given in the username and password fields. Generally, for security reasons, it is not a good idea for this user to have "superuser" privileges. However, the adapter does need superuser privileges for one function: installing PostGIS into the database when the database is first created. Therefore, you should provide a second set of credentials, su_username and su_password, which identify a superuser account. This account will be used once, when you create the database (i.e. rake db:create), and not afterward.

Schema Dump and Reload

The presence of geospatial data in a database causes some issues with ActiveRecord's schema dump and restore functions. This is because (1) installing PostGIS into your database injects a lot of objects in your database that can clutter up schema dumps, and (2) to define a spatial column correctly, you generally must call a SQL function such as AddGeometryColumn(), and Rails's schema dumper isn't smart enough to reproduce those function calls.

Because of this, we recommend the following:

  • Install the PostGIS definitions in a separate schema called "postgis" (as described in the recommended installation procedure above). The activerecord-postgis-adapter will ignore a schema called "postgis" when dumping the schema, thus omitting the clutter.

  • Set the ActiveRecord schema format to :ruby, not :sql. The former emits higher level commands that can be interpreted correctly to reproduce the schema. The latter, however, emits low level SQL, which loses information such as the fact that AddGeometryColumn() was originally used to generate a column. Executing a :sql format schema dump will not correctly reproduce the schema.

Of course, the above discussion is really relevant only if you are using the ActiveRecord rake tasks that create and restore databases, either directly such as rake db:create or indirectly such as rake test. It does not have any effect on running migrations or normal website execution.