FAQ

:include:QUICKLINKS

= FAQ

=== So where's my :id column?

DataMapper will NOT create an auto-incrementing <tt>:id</tt> key for you 
automatically, so you'll need to either explicitly create one with

  property :id, Serial

You can choose to use a natural key by doing

  property :slug, String, :key => true

Remember, DataMapper supports multiple keys ("composite keys"), so if your
model has two or more keys, no big deal

  property :store_id, 	Integer, :key => true
  property :invoice_id, Integer, :key => true

=== How do I make a model paranoid?

Create a property and make it a ParanoidDateTime or ParanoidBoolean type.

  property :deleted_at, ParanoidDateTime
  property :deleted,    ParanoidBoolean

All of your calls to <tt>##all()</tt>, <tt>##first()</tt> will be scoped 
with <tt>:deleted_at => nil</tt> or <tt>:deleted => false</tt>. Plus, 
you won't see deleted objects in your associations.

=== Does DataMapper do Single Table Inheritance?

This is what the Discriminator data-type is for:

  class Person
    include DataMapper::Resource

    property :id,   Serial
    property :type, Discriminator  ## other shared properties here
  end

  class Salesperson < Person; end

You can claim a column to have the type <tt>Discriminator</tt> and DataMapper will
automatically drop the class name of the inherited classes into that field of
the data-store.

=== How do I run my own commands?

  repository.adapter.query("SELECT * FROM users WHERE clue > 0")
  repository(:integration).adapter.query("SELECT * FROM users WHERE clue > 0")

This does not return any Users (har har), but rather Struct's that will quack
like Users. They'll be read-only as well.

<tt>repository.adapter.query</tt> shouldn't be used if you aren't expecting a result set
back.  If you want to just execute something against the database, use
<tt>repository.adapter.execute</tt> instead.


=== Can I get an query log of what DataMapper is issuing?

An example of how to modify an existing logger:

  DataMapper.logger.set_log(STDOUT, :debug)

An example of how to create new logger:

  DataMapper::Logger.new(STDOUT, :info)

To send a message to the DataMapper logger:

  DataMapper.logger.debug("something")
  DataMapper.logger.info ("something")
  DataMapper.logger.warn ("something")
  DataMapper.logger.error("something")
  DataMapper.logger.fatal("something")


=== I want to run the specs, but I have a custom database setup

For example, if you installed MySQL using MacPorts, your socket may be located
at /opt/local/var/run/mysql5/mysqld.sock instead of /tmp/mysql.sock

In that case, setup an environment variable in your shell before running the
specs:
  export MYSQL_SPEC_URI="mysql://localhost/dm_core_test?socket=/opt/local/var/run/mysql5/mysqld.sock"
  rake spec

Using another kind of database? Note that spec_helper.rb will also look for
SQLITE3_SPEC_URI AND POSTGRES_SPEC_URI.