Rails 3 date field is blank after form submit - ruby-on-rails

Question

Rails newbie here.
I have 2 models: Target and Observation
Target works fine. I generated scaffolding for Observation, like this:
rails generate scaffold Observation date:date target:references
So app/models/observation.rb says:
class Observation < ActiveRecord::Base
belongs_to :target
end
Then I edited app/models/target.rb:
class Target < ActiveRecord::Base
has_many :observations
end
The scaffolding created app/views/observations/_form.html.erb which includes:
<div class="field">
<%= f.label :target %><br />
<%= f.text_field :target %>
</div>
And app/controllers/observation_controller.rb which includes:
def create
#observation = Observation.new(params[:observation])
I then go to create a new Observation. I enter a date and the ID of a target in the target field. When I submit, I get this error in the browser:
ActiveRecord::AssociationTypeMismatch in ObservationsController#create
Target(#2190392620) expected, got String(#2148287480)
Seems like the scaffolding would set up something that would work. But the error makes sense. It's receiving the ID of the Target instead of the Target itself. So I edited app/controllers/observation_controller.rb to say:
def create
#target = Target.find(params[:observation][:target])
#observation = #target.observations.create(:date => params[:observation][:date])
Now it creates the Observation record, with the reference to the Target. But the date field is blank.
I realize this may be a dumb newbie or RTFM question, but I'd really appreciate a pointer in the right direction. Thanks.
Here's the full contents of the form, after changing it to reflect the answer received.
<%= form_for(#observation) do |f| %>
<% if #observation.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#observation.errors.count, "error") %> prohibited this observation from being saved:</h2>
<ul>
<% #observation.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :date %><br />
<%= f.date_select :date %>
</div>
<div class="field">
<%= f.label :target %><br />
<%= f.collection_select :target_id, Target.all, :id, :name %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>

Answer 1

change
<%= f.text_field :target %>
to
<%= f.text_field :target_id %>
And really better is to use something like select for this thing. Like:
<%= f.collection_select :target_id, Target.all, :id, :title %>
UPD
As far as date_select helper set not ordinary banch of variables for each element (year, month, day) you shoul do this:
date = [ params[:observation]['date(1i)'], params[:observation]['date(2i)'], params[:observation]['date(3i)'] ].join(".")
#observation = #target.observations.create(:date => date)
Actually just look into HTML source and you'll see it

Answer 2

(Not sure if you are still monitoring this, OP? For the benefit of everyone coming here via Google:)
There will be no params[:observation][:date] because dates are entered using several HTML input fields, and then magically merged in assignment. The keyword for this is "multi-parameter attributes", and this is the best explanation I've found:
How do ruby on rails multi parameter attributes *really* work (datetime_select)
I also wonder if this simpler snippet would work.
#observation = #target.observations.create(params[:observation])

Answer 3

You can use:
<%= collection_select(:observation, :target_id, Target.all, :id, :title %>
i think it will help you.