[Rails] How to work with non-autogenerated primary keys

Oddly enough, I have not found a clear explanation of how to make ActiveRecord work with a table that has a non-autogenerated primary key. In other words, the table has a column as a primary key for which the value has to be inserted manually. (Of course this is not good practice but what other better reason to do this than to say such a table already exists and needed a user interface for maintaining its values!)
So how do we go about doing this? Simple. First, set the primary key in the Model object to be the column in the table (since ActiveRecord always assumes primary key is a column called "id"). If we just run this and try to save the model object by firing up the rails console, rails gives an error saying there are no attributes "col1". This is because, rails assumes that the primary key is not editable. So all we have to do is define attributes for the primary key column col1. The overall changes are shown below:

class MyModel < ActiveRecord::Base

set_primary_key "col1"
def col1
read_attribute "col1"
end
def col1=(value)
write_attribute "col1", value
end

end

Now fire up the rails console and create and save the model object, setting values for the required columns. Voila!

Note: since you are departing a bit from rails convention of primary keys, you will need to make sure that the required validations are added in the model so that you dont get errors from the database.