Unfortunately, I’ve determined it’s not possible to do it without using execute
.
Why it doesn’t work
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"
The workaround
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