I'm using Rails migrations to manage a database schema, and I'm creating a simple table where I'd like to use a non-integer value as the primary key (in particular, a string). To abstract away from my problem, let's say there's a table employees
where employees are identified by an alphanumeric string, e.g. "134SNW"
.
I've tried creating the table in a migration like this:
create_table :employees, {:primary_key => :emp_id} do |t|
t.string :emp_id
t.string :first_name
t.string :last_name
end
What this gives me is what seems like it completely ignored the line t.string :emp_id
and went ahead and made it an integer column. Is there some other way to have rails generate the PRIMARY_KEY constraint (I'm using PostgreSQL) for me, without having to write the SQL in an execute
call?
NOTE: I know it's not best to use string columns as primary keys, so please no answers just saying to add an integer primary key. I may add one anyway, but this question is still valid.
Unfortunately, I've determined it's not possible to do it without using execute
.
By examining the ActiveRecord source, we can find the code for create_table
:
def create_table(table_name, options={})
...
table_definition.primary_key(options[:primary_key] || Base.get_primary_key(table_name.to_s.singularize)) unless options[:id] == false
...
end
So we can see that when you try to specify a primary key in the create_table
options, it creates a primary key with that specified name (or, if none is specified, id
). It does this by calling the same method you can use inside a table definition block: primary_key
.
def primary_key(name)
column(name, :primary_key)
end
This just creates a column with the specified name of type :primary_key
. This is set to the following in the standard database adapters:
PostgreSQL: "serial primary key"
MySQL: "int(11) DEFAULT NULL auto_increment PRIMARY KEY"
SQLite: "INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL"
Since we're stuck with these as the primary key types, we have to use execute
to create a primary key that is not an integer (PostgreSQL's serial
is an integer using a sequence):
create_table :employees, {:id => false} do |t|
t.string :emp_id
t.string :first_name
t.string :last_name
end
execute "ALTER TABLE employees ADD PRIMARY KEY (emp_id);"
And as Sean McCleary mentioned, your ActiveRecord model should set the primary key using set_primary_key
:
class Employee < ActiveRecord::Base
set_primary_key :emp_id
...
end