method

new

v1.1.6 - Show latest stable - 3 notes - Class: ActiveRecord::Base

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What's this?

new(attributes = nil) public

New objects can be instantiated as either empty (pass no construction parameter) or pre-set with attributes but not yet saved (pass a hash with key names matching the associated table column names). In both instances, valid attribute keys are determined by the column names of the associated table — hence you can’t have attributes that aren’t part of the table columns.

Show source

# File activerecord/lib/active_record/base.rb, line 1350 def initialize(attributes = nil) @attributes = attributes_from_column_definition @new_record = true ensure_proper_type self.attributes = attributes unless attributes.nil? yield self if block_given? end

April 16, 2009

3 thanks

Various use cases

Example

user = User.new user.name = 'Akhil Bansal' user.save user = User.new(:name => 'Akhil') user.save User.new do |u| u.name = 'Akhil' u.save end

March 24, 2010

1 thank

Setting primary key from hash

If you try to specify the value for your primary key (usually “id”) through the attributes hash, it will be stripped out:

Post.new(:id => 5, :title => 'Foo') #=> #<Post @id=nil @title="Foo">

You can solve this by setting it directly, perhaps by using a block:

Post.new(:title => "Foo") { |p| p.id = 5 } #=> #<Post @id=5 @title="Foo">

This behavior is something you’d probably only have a problem with when you have custom primary keys. Perhaps you have a User model with a primary key of “name”…

class User < ActiveRecord::Base set_primary_key :name end User.new(params[:user]) # This will never work

You can solve this on a case-to-case basis by calling attributes= directly with the “ignore protected” option:

User.new { |user| user.send(:attributes=, params[:user], false) } # BAD BAD BAD!

You should not do the above example, though. If you do, all protected attributes are ignored, which is very, very bad when you only care about the primary key.

I’d recommend one of the following instead:

# Option 1 – Always allow primary key. Avoid with models created by users class User private def attributes_protected_by_default super - [self.class.primary_key.to_s] end end # Option 2 – Add a new method for this case class User def self.new_with_name(attributes = nil) new(attributes) { |u| u.name = attributes[:name] } end end

As always when something is hard to do in Rails: Think about your design? Is it recommended? Is it sound? Do you really need to have a custom primary key?

July 30, 2014 - (>= v4.0.2)

0 thanks

4.0.2 support

Where did this go in 4.0.2?

new

Related methods

Various use cases

Example

Setting primary key from hash

4.0.2 support