在 ActiveRecord 中重写创建时的 id

Try

a_post = Post.new do |p|
p.id = 10
p.title = 'Test'
p.save
end

that should give you what you're looking for.

Actually, it turns out that doing the following works:

p = Post.new(:id => 10, :title => 'Test')
p.save(false)

id is just attr_protected, which is why you can't use mass-assignment to set it. However, when setting it manually, it just works:

o = SomeObject.new
o.id = 8888
o.save!
o.reload.id # => 8888

I'm not sure what the original motivation was, but I do this when converting ActiveHash models to ActiveRecord. ActiveHash allows you to use the same belongs_to semantics in ActiveRecord, but instead of having a migration and creating a table, and incurring the overhead of the database on every call, you just store your data in yml files. The foreign keys in the database reference the in-memory ids in the yml.

ActiveHash is great for picklists and small tables that change infrequently and only change by developers. So when going from ActiveHash to ActiveRecord, it's easiest to just keep all of the foreign key references the same.

As Jeff points out, id behaves as if is attr_protected. To prevent that, you need to override the list of default protected attributes. Be careful doing this anywhere that attribute information can come from the outside. The id field is default protected for a reason.

class Post < ActiveRecord::Base


private


def attributes_protected_by_default
[]
end
end

(Tested with ActiveRecord 2.3.5)

we can override attributes_protected_by_default

class Example < ActiveRecord::Base
def self.attributes_protected_by_default
# default is ["id", "type"]
["type"]
end
end


e = Example.new(:id => 10000)

Put this create_with_id function at the top of your seeds.rb and then use it to do your object creation where explicit ids are desired.

def create_with_id(clazz, params)
obj = clazz.send(:new, params)
obj.id = params[:id]
obj.save!
obj
end

and use it like this

create_with_id( Foo, {id:1,name:"My Foo",prop:"My other property"})

instead of using

Foo.create({id:1,name:"My Foo",prop:"My other property"})

Post.create!(:title => "Test") { |t| t.id = 10 }

This doesn't strike me as the sort of thing that you would normally want to do, but it works quite well if you need to populate a table with a fixed set of ids (for example when creating defaults using a rake task) and you want to override auto-incrementing (so that each time you run the task the table is populate with the same ids):

post_types.each_with_index do |post_type|
PostType.create!(:name => post_type) { |t| t.id = i + 1 }
end

You could also use something like this:

Post.create({:id => 10, :title => 'Test'}, :without_protection => true)

Although as stated in the docs, this will bypass mass-assignment security.

This case is a similar issue that was necessary overwrite the id with a kind of custom date :

# in app/models/calendar_block_group.rb
class CalendarBlockGroup < ActiveRecord::Base
...
before_validation :parse_id


def parse_id
self.id = self.date.strftime('%d%m%Y')
end
...
end

And then :

CalendarBlockGroup.create!(:date => Date.today)
# => #<CalendarBlockGroup id: 27072014, date: "2014-07-27", created_at: "2014-07-27 20:41:49", updated_at: "2014-07-27 20:41:49">

Callbacks works fine.

Good Luck!.

For Rails 3, the simplest way to do this is to use new with the without_protection refinement, and then save:

Post.new({:id => 10, :title => 'Test'}, :without_protection => true).save

For seed data, it may make sense to bypass validation which you can do like this:

Post.new({:id => 10, :title => 'Test'}, :without_protection => true).save(validate: false)

We've actually added a helper method to ActiveRecord::Base that is declared immediately prior to executing seed files:

class ActiveRecord::Base
def self.seed_create(attributes)
new(attributes, without_protection: true).save(validate: false)
end
end

And now:

Post.seed_create(:id => 10, :title => 'Test')

For Rails 4, you should be using StrongParams instead of protected attributes. If this is the case, you'll simply be able to assign and save without passing any flags to new:

Post.new(id: 10, title: 'Test').save      # optionally pass `{validate: false}`

For Rails 4:

Post.create(:title => 'Test').update_column(:id, 10)

Other Rails 4 answers did not work for me. Many of them appeared to change when checking using the Rails Console, but when I checked the values in MySQL database, they remained unchanged. Other answers only worked sometimes.

For MySQL at least, assigning an id below the auto increment id number does not work unless you use update_column. For example,

p = Post.create(:title => 'Test')
p.id
=> 20 # 20 was the id the auto increment gave it


p2 = Post.create(:id => 40, :title => 'Test')
p2.id
=> 40 # 40 > the next auto increment id (21) so allow it


p3 = Post.create(:id => 10, :title => 'Test')
p3.id
=> 10 # Go check your database, it may say 41.
# Assigning an id to a number below the next auto generated id will not update the db

If you change create to use new + save you will still have this problem. Manually changing the id like p.id = 10 also produces this problem.

In general, I would use update_column to change the id even though it costs an extra database query because it will work all the time. This is an error that might not show up in your development environment, but can quietly corrupt your production database all the while saying it is working.

In Rails 4.2.1 with Postgresql 9.5.3, Post.create(:id => 10, :title => 'Test') works as long as there isn't a row with id = 10 already.

you can insert id by sql:

  arr = record_line.strip.split(",")
sql = "insert into records(id, created_at, updated_at, count, type_id, cycle, date) values(#{arr[0]},#{arr[1]},#{arr[2]},#{arr[3]},#{arr[4]},#{arr[5]},#{arr[6]})"
ActiveRecord::Base.connection.execute sql