Documentation

API: The API for the current gem release.
Why DataMapper?: If you haven't read this yet, you should, right now!
Getting Started: A whirlwind tour of DM. This is the place to start if you haven't used the library before.
Common installation issues: Troubleshooting installation, with instructions for specific platforms.
Properties: Properties declared in your model map to the fields in the database.
Creating, Saving, Updating and Destroying Records: Obviously you're going to be doing a lot of this :)
Validations: Auto-validations, manual validations, contextual validations
Finding and Counting Records: There are lots of nice ways to find records.
Associations: Models can be associated to each other in various ways using the has keyword
Hooks: Hooks, AKA Callbacks, allow you to "advise other methods" by running methods before or after calling other methods.
Misc. Features: Paranoia, Single Table Inheritance, and Multiple Repositories.
More: Plugins galore for DataMapper.

Documentarians Wanted!

Want to help DataMapper, but don’t know where to start? A great way to contribute is to help out in the documentation effort.

Documentation Style

DataMapper uses the YARD standard for RDoc documentation. Here’s a brief sample from the internals of DM-Core:

 1 # Setups up a connection to a data-store
 2 #
 3 # @param [Symbol] name
 4 #   a name for the context, defaults to :default
 5 # @param [Hash(Symbol => String), Addressable::URI, String] uri_or_options
 6 #   connection information
 7 #
 8 # @return [DataMapper::Adapters::AbstractAdapter]
 9 #   the resulting setup adapter
10 #
11 # @raise [ArgumentError] "+name+ must be a Symbol, but was..."
12 #   indicates that an invalid argument was passed for name[Symbol]
13 # @raise [ArgumentError] "+uri_or_options+ must be a Hash, URI or String, but was..."
14 #   indicates that connection information could not be gleaned from
15 #   the given uri_or_options[Hash, Addressable::URI, String]
16 #
17 # @api public
18 def self.setup(name, uri_or_options)
19   raise ArgumentError, "+name+ must be a Symbol, but was #{name.class}", caller unless Symbol === name
20   ...

For more information about the YARD documentation style, see the YARD Getting Started document.