How to Set The Starting Point for The Primary Key (Id) Column in Postgres via a Rails Migration

How can I set the starting point for the primary key (ID) column in Postgres via a rails migration

Have no idea about rubies and railroads part, but query you're talking about is

ALTER SEQUENCE reports_something_seq RESTART 1000;

You will have to look up your table for the sequence name and postgresql documentation for general education regarding the matter ;-)

Add primary key to an existing field in Rails

I ended up doing this:

execute('ALTER TABLE inventories ADD PRIMARY KEY (id);')

Using Rails, how can I set my primary key to not be an integer-typed column?

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:

In schema_statements.rb:

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.

In schema_statements.rb:

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

Insert sequence value in a column within the scope of a foreign key - Rails and Postgres

There is a gem called sequenced. I thought it will solve your problem.

Sequenced is a simple gem that generates scoped sequential IDs for
ActiveRecord models. This gem provides an acts_as_sequenced macro that
automatically assigns a unique, sequential ID to each record. The
sequential ID is not a replacement for the database primary key, but
rather adds another way to retrieve the object without exposing the
primary key.

---

The gem provides a Ruby/Rails implementation. It used ActiveModel::Callbacks to set the value of sequential_id column: before_save :set_sequential_ids [link].

def acts_as_sequenced(options = {})
  # ...
  include Sequenced::ActsAsSequenced::InstanceMethods

  mattr_accessor :sequenced_options, instance_accessor: false

  self.sequenced_options = []

  before_save :set_sequential_ids
  # ...
end

Here is the setter method [link]:

def set
  return if id_set? || skip?
  lock_table
  record.send(:"#{column}=", next_id)
end

How to change primary key in rails migration file?

You could execute arbitrary SQL in your migration:

execute "ALTER TABLE `products` DROP PRIMARY KEY"

and then add the new column:

add_column :products, :id, :primary_key

See:

Remove Primary Key in MySQL

how to add a primary key to a table in rails

http://thinkwhere.wordpress.com/2009/05/09/adding-a-primary-key-id-to-table-in-rails/

http://api.rubyonrails.org/classes/ActiveRecord/Migration.html

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