I’m using Rails 4.2.7. I have an attribute in my model that doesn’t have a database field underneath it
attr_accessor :division
This gets initialized when I create a new object.
my_object = MyObject.new(:name => name,
:age => get_age(data_hash),
:overall_rank => overall_rank,
:city => city,
:state => state,
:country => country,
:age_group_rank => age_group_rank,
:gender_rank => gender_rank,
:division => division)
What I would like is when this field gets set (if it is not nil), for two other fields that do have mappings in the database to get set. The other fields would be substrings of the “division” field. Where do I put that logic?
I'd probably drop the attr_accessor :division and do it by hand with:
def division=(d)
# Break up `d` as needed and assign the parts to the
# desired real attributes.
end
def division
# Combine the broken out attributes as needed and
# return the combined string.
end
With those two methods in place, the following will all call division=:
MyObject.new(:division => '...')
MyObject.create(:division => '...')
o = MyObject.find(...); o.update(:division => '...')
o = MyObject.find(...); o.division = '...'
so the division and the broken out attributes will always agree with each other.
If you try to use one of the lifecycle hooks (such as after_initialize) then things can get out of sync. Suppose division has the form 'a.b' and the broken out attributes are a and b and suppose that you're using one of the ActiveRecord hooks to break up division. Then saying:
o.division = 'x.y'
should give you o.a == 'x' but it won't because the hook won't have executed yet. Similarly, if you start with o.division == 'a.b' then
o.a = 'x'
won't give you o.division == 'x.b' so the attributes will have fallen out of sync again.
I see couple of options here
You can add it in your controller as follows
def create
if params[:example][:division]
# Set those params here
end
end
Or you can use before_save In your model
before_save :do_something
def do_something
if division
# Here!
end
end
I am wondering if it's possible to reference an object's attribute.
The object User have attribute first_name, so normally if we want to update the first name attribute we do:
user0 = User.new()
user0.update_attribute(:first_name, "joe")
now my question is can I update the :first_name attribute through another variable/symbol like so:
user0.update_attribute(:fname_ref, "jack")
user0.first_name #=> has the value jack
I was looking for variable reference like in Perl, but came up nothing in Ruby.
---------- EDIT
I am in the middle of doing the lynda ruby on rails tutorial, and in the middle of creating a module to adjust positions of items in a table.
unfortunately when I first started I named my tables columns differently
pages.page_position, subjects.subject_position, sections.section_position
now the module PositionMover is to be used accross three models, so now
I have a problem since the attributes names are different for each model
so I thought no worry I'll just create a pointer / refference for each model
:position = :pages_position , :position = :subjects_position , :position = :section_position
hence the question , if its even possible to do it.
if its not possible , any suggestion what should I do , so the module can
be used accross three different models , with different attribute names.
sorry I am a newbie.
Symbols are not like variables, they are actually a object type, like String or Fixnum so you can have a variable that is of type symbol.
I think this is what you are looking for:
attribute = :first_name
user0.update_attribute(attribute, "jack")
user0.first_name #=> has the value jack
Update: If you have a String and need to convert to a symbol, (I'm not sure if you need this for update_attribute)
foo = "string"
foo.to_sym #=> :string
Use the alias_attribute . Define into each model like :
Page model
alias_attribute :position , :pages_position
Subject Model
alias_attribute :position , :subjects_position
Section Model
alias_attribute :position , :section_position
And use (Model.position = values) with each model . Hope Its solution of your problem .
You can also use send docs and use symbols or strings to reference the attribute's methods. send can be incredibly useful since it enables you to choose the method that you'll be invoking at runtime.
Eg
user.first_name = "Jack" # set first_name to Jack
# Note: method "first_name=" (a settor) is being used
attribute = "first_name"
user.send attribute + "=", "Jack" # set first_name to Jack
# The string "first_name=" is coerced into
# a symbol
attribute = :first_name
val = user.send attribute # => returns "Jack"
see the definition of update_attribute in the ActiveRecord::Persistence module on github:
def update_attribute(name, value)
name = name.to_s
verify_readonly_attribute(name)
send("#{name}=", value)
save(:validate => false)
end
this leads me to believe you could add the following to your model to achieve that behavior:
alias_method :fname_ref= :first_name=
I'd be interested to know why you want to do that as #Andrew Marshall asked.
Here's some of my production code (I had to force line breaks):
task = Task.find_or_create_by_username_and_timestamp_and_des \
cription_and_driver_spec_and_driver_spec_origin(username,tim \
estamp,description,driver_spec,driver_spec_origin)
Yes, I'm trying to find or create a unique ActiveRecord::Base object. But in current form it's very ugly. Instead, I'd like to use something like this:
task = Task.SOME_METHOD :username => username, :timestamp => timestamp ...
I know about find_by_something key=>value, but it's not an option here. I need all values to be unique. Is there a method that'll do the same as find_or_create_by, but take a hash as an input? Or something else with similat semantics?
Rails 3.2 first introduced first_or_create to ActiveRecord. Not only does it have the requested functionality, but it also fits in the rest of the ActiveRecord relations:
Task.where(attributes).first_or_create
In Rails 3.0 and 3.1:
Task.where(attributes).first || Task.create(attributes)
In Rails 2.1 - 2.3:
Task.first(:conditions => attributes) || Task.create(attributes)
In the older versions, you could always write a method called find_or_create to encapsulate this if you'd like. Definitely done it myself in the past:
class Task
def self.find_or_create(attributes)
# add one of the implementations above
end
end
I also extend the #wuputah's method to take in an array of hashes, which is very useful when used inside db/seeds.rb
class ActiveRecord::Base
def self.find_or_create(attributes)
if attributes.is_a?(Array)
attributes.each do |attr|
self.find_or_create(attr)
end
else
self.first(:conditions => attributes) || self.create(attributes)
end
end
end
# Example
Country.find_or_create({:name => 'Aland Islands', :iso_code => 'AX'})
# take array of hashes
Country.find_or_create([
{:name => 'Aland Islands', :iso_code => 'AX'},
{:name => 'Albania', :iso_code => 'AL'},
{:name => 'Algeria', :iso_code => 'DZ'}
])
Is there a way I can know what attributes are updated in my model? I only want to do a validation on a user when a certain attribute was posted. This would actually be the hash that is sent via the params
eg:
#user.update_attributes(params[:user])
Thanks.
This is available within the ActiveRecord::Dirty module, which is included by default.
The changed method will give you a list of attributes with unsaved changes. The changes method will give you a hash of unsaved changes, where the keys are the attribute names and the values are an array consisting of the original and new value.
For example:
#user.changed # => ['name', 'age']
#user.changes # => { 'name' => ['Bill', 'John'], 'age' => [18, 21] }
Is there any way of overriding a model's id value on create? Something like:
Post.create(:id => 10, :title => 'Test')
would be ideal, but obviously won't work.
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.
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.
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.
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.
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)
Actually, it turns out that doing the following works:
p = Post.new(:id => 10, :title => 'Test')
p.save(false)
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)
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
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"})
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}`
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