I'm working on building an app to keep track of product designs, and I'm having some trouble with my associations. Basically I have a model (Assembly) which needs to have polymorphic association, but also needs to be able to belong to itself.
To illustrate, I have three models: Product, Assembly, and Part.
A Product can have many Assemblies.
An Assembly can have many Parts AND Assemblies.
An Assembly belongs to a Product OR an Assembly.
A Part belongs to an Assembly.
My model definitions are currently like this:
product.rb
class Product < ActiveRecord::Base
belongs_to :product_family
has_many :assemblies, as: :assemblable
end
assembly.rb
class Assembly < ActiveRecord::Base
belongs_to :assemblable, polymorphic: true
has_many :parts
has_many :subassemblies, as: :assemblable
end
part.rb
class Part < ActiveRecord::Base
belongs_to :assembly
belongs_to :product_family
end
What I would like to be able to do is, given an assembly called "top_assy":
top_assy.subassemblies.create
However, when I try this, I get the following error:
NameError: uninitialized constant Assembly::Subassembly
I'm clearly doing something wrong here - what am I missing? I have already tried adding 'class_name: "Assembly"' as an argument to the 'has_many :subassemblies' command.
Thanks in advance!
has_many :subassemblies, as: :assemblable
by
has_many :subassemblies, as: :assemblable, class_name: 'Assembly'
Carlos's solution works because now rails knows which class to query, as follows:
Before specifying :class_name:
When calling .subassemblies method, rails queries a supposed 'Subassembly' model class to match the 'assemblable_id' column in that class. However, 'Subassembly' model class is not defined (it doesn't make sense to define it anyway) here and hence the error.
After specifying :class_name:
Because the class 'Assembly' was specified as :class_name, now rails knows it is to query the 'Assembly' model class and match the 'assemblable_id' column.
Demonstation of flow:
# :class_name has been specified to be 'Assembly'
ex_asm = Assembly.new # an example assembly
ex_asm.subassemblies # flow:
# 1. Rails checks the :subassemblies association
# 2.a. There it is specified to query the class 'Assembly'
# 2.b. and it is to match the "id" column of ex_asm
# 2.c. with the 'assemblable_id' column of the Assembly table
# 3 Rails returns the assemblies matching criteria (2) as
# :subassemblies of ex_asm.
I don't know why this works, but I had the same problem and solve as it:
In Assembly class replace
has_many :subassemblies, as: :assemblable
by
has_many :subassemblies, as: :assemblable, class_name: 'Assembly'
=====================================================================
Edit: explanation of solution
Before specifying :class_name:
When calling .subassemblies method, rails queries a supposed 'Subassembly' model class to match the 'assemblable_id' column in that class. However, 'Subassembly' model class is not defined (it doesn't make sense to define it anyway) here and hence the error.
After specifying :class_name:
Because the class 'Assembly' was specified as :class_name, now rails knows it is to query the 'Assembly' model class and match the 'assemblable_id' column.
Demonstation of flow:
# :class_name has been specified to be 'Assembly'
ex_asm = Assembly.new # an example assembly
ex_asm.subassemblies # flow:
# 1. Rails checks the :subassemblies association
# 2.a. There it is specified to query the class 'Assembly'
# 2.b. and it is to match the "id" column of ex_asm
# 2.c. with the 'assemblable_id' column of the Assembly table
# 3 Rails returns the assemblies matching criteria (2) as
# :subassemblies of ex_asm.
you can try this
product.rb
class Product < ActiveRecord::Base
belongs_to :product_family
has_many :assemblies
end
assembly.rb
class Assembly < ActiveRecord::Base
attr_accessible :top_assembly_id
has_many :sub_assemblies, :class_name => "Assembly", :foreign_key => "top_assembly_id"
belongs_to :top_assembley, :class_name => "Assembly"
has_many :parts
end
part.rb
class Part < ActiveRecord::Base
belongs_to :assembly
belongs_to :product_family
end
and now you can referer
top_assembley.sub_assemblies.create
Related
I have a parent class Individual and child classes Student and Professor in my rails application.
Inheritance is handled with a gem called 'acts_as_relation' which simulates multiple table inheritance.
In addition, I have an action within which a student instance is appended to a list of individuals. Normally I would have expected this to go through without any problems but I get this error:
ActiveRecord::AssociationTypeMismatch: Individual(#70220161296060) expected, got Student(#70220161349360)
Here is a glance at my model:
class Individual < ActiveRecord::Base
acts_as_superclass
end
class Student < ActiveRecord::Base
acts_as :individual
end
class Professor < ActiveRecord::Base
acts_as :individual
end
I've not used this gem, but to give you some help, here's what I've found and this:
They both mention that you're calling an object through your relation, which will have confusion over polymorphism or similar. The two posts could not fix the issue, and I presume that is because they could find the correct object for their relationship
Looking at this further, I found this tutorial on the gem homepage:
acts_as_relation uses a polymorphic has_one association to simulate
multiple-table inheritance. For the e-commerce example you would
declare the product as a supermodel and all types of it as acts_as
:product (if you prefer you can use their aliases is_a and
is_a_superclass)
class Product < ActiveRecord::Base
acts_as_superclass
end
class Pen < ActiveRecord::Base
acts_as :product
end
class Book < ActiveRecord::Base
acts_as :product
end
To make this work, you need to declare both a foreign key column and a
type column in the model that declares superclass. To do this you can
set :as_relation_superclass option to true on products create_table
(or pass it name of the association):
create_table :products, :as_relation_superclass => true do |t|
# ...
end
Or declare them as you do on a polymorphic belongs_to association, it
this case you must pass name to acts_as in :as option:
change_table :products do |t|
t.integer :producible_id
t.string :producible_type
end
class Pen < ActiveRecord::Base
acts_as :product, :as => :producible
end
class Book < ActiveRecord::Base
acts_as :product, :as => :producible
end
Are you sure you've got your datatables set up correctly?
The way I've solve this in my projects, is using instance_ofsome_class.individuals << student_instance.individual.
The thing here is that is not a real MTI, so your collection of individuals would accept only individuals instances. If you call some_student_instance.individual or some_professor_instance.individual, you'll get an individual instance which is related with your specific instance.
Then working with that collection, if you want a Student or Professor all you need to do is call individual_in_collection.specific. For example:
p = Professor.create
a_model.individuals << p.individual
puts "#{a_model.individuals.first.class.name}"
=> Individual
puts "#{a_model.individuals.first.specific.class.name}"
=> Professor
I have a Sponsors model and a Promo Codes model.
A sponsor can have zero or more promo codes
A promo code can have zero or one sponsors
Thus a promo code should have an optional reference to a sponsor, that is, a sponsor_id that may or may not have a value. I'm not sure how to set this up in Rails.
Here's what I have so far:
# app/models/sponsor.rb
class Sponsor < ActiveRecord::Base
has_many :promo_codes # Zero or more.
end
# app/models/promo_code.rb
class PromoCode < ActiveRecord::Base
has_one :sponsor # Zero or one.
end
# db/migrate/xxxxx_add_sponsor_reference_to_promo_codes.rb
# rails g migration AddSponsorReferenceToPromoCodes sponsor:references
# Running migration adds a sponsor_id field to promo_codes table.
class AddSponsorReferenceToPromoCodes < ActiveRecord::Migration
def change
add_reference :promo_codes, :sponsor, index: true
end
end
Does this make sense? I'm under the impression that I have to use belongs_to in my Promo Codes model, but I have no basis for this, just that I've haven't seen a has_many with has_one example yet.
In Rails 5, belongs_to is defined as required by default. To make it optional use the 'optional' option :)
class User
belongs_to :company, optional: true
end
Source: https://github.com/rails/rails/issues/18233
This looks like a simple has_many and belongs_to relationship:
# app/models/sponsor.rb
class Sponsor < ActiveRecord::Base
has_many :promo_codes # Zero or more.
end
# app/models/promo_code.rb
#table has sponsor_id field
class PromoCode < ActiveRecord::Base
belongs_to :sponsor # Zero or one.
end
has_one isn't appropriate here, as it would replace has_many: ie, you either have "has_many" and "belongs_to" OR "has_one" and "belongs_to". has_one isn't generally used much: usually it is used when you already have a has_many relationship that you want to change to has_one, and don't want to restructure the existing tables.
Unless you specify validation, relationships are optional by default.
The belongs_to is to tell rails the other half of the relationship between those two objects so you can also call #promo_code.sponsor and, vice versa, #sponsor.promo_codes.
Setup
For this question, I'll use the following three classes:
class SolarSystem < ActiveRecord::Base
has_many :planets
scope :has_earthlike_planet, joins(:planets).merge(Planet.like_earth)
end
class Planet < ActiveRecord::Base
belongs_to :solar_system
belongs_to :planet_type
scope :like_earth, joins(:planet_type).where(:planet_types => {:life => true, :gravity => 9.8})
end
class PlanetType < ActiveRecord::Base
has_many :planets
attr_accessible :gravity, :life
end
Problem
The scope has_earthlike_planet does not work. It gives me the following error:
ActiveRecord::ConfigurationError: Association named 'planet_type' was
not found; perhaps you misspelled it?
Question
I have found out that this is because it is equivalent to the following:
joins(:planets, :planet_type)...
and SolarSystem does not have a planet_type association. I'd like to use the like_earth scope on Planet, the has_earthlike_planet on SolarSystem, and would like to avoid duplicating code and conditions. Is there a way to merge these scopes like I'm attempting to do but am missing a piece? If not, what other techniques can I use to accomplish these goals?
Apparently, at this time you can only merge simple constructs that don't involve joins. Here is a possible workaround if you modify your models to look like this:
class SolarSystem < ActiveRecord::Base
has_many :planets
has_many :planet_types, :through => :planets
scope :has_earthlike_planet, joins(:planet_types).merge(PlanetType.like_earth)
end
class Planet < ActiveRecord::Base
belongs_to :solar_system
belongs_to :planet_type
scope :like_earth, joins(:planet_type).merge(PlanetType.like_earth)
end
class PlanetType < ActiveRecord::Base
has_many :planets
attr_accessible :gravity, :life
scope :like_earth, where(:life => true, :gravity => 9.8)
end
** UPDATE **
For the record, a bug was filed about this behavior - hopefully will be fixed soon...
You are reusing the conditions from the scope Planet.like_earth, which joins planet_type. When these conditions are merged, the planet_type association is being called on SolarSystem, which doesn't exist.
A SolarSystem has many planet_types through planets, but this is still not the right association name, since it is pluralized. You can add the following to the SolarSystem class to setup the planet_type association, which is just an alias for planet_types. You can't use the Ruby alias however since AREL reflects on the association macros, and doesn't query on whether the model responds to a method by that name:
class SolarSystem < ActiveRecord::Base
has_many :planets
has_many :planet_types, :through => :planets
has_many :planet_type, :through => :planets, :class_name => 'PlanetType'
scope :has_earthlike_planet, joins(:planets).merge(Planet.like_earth)
end
SolarSystem.has_earthlike_planet.to_sql # => SELECT "solar_systems".* FROM "solar_systems" INNER JOIN "planets" ON "planets"."solar_system_id" = "solar_systems"."id" INNER JOIN "planets" "planet_types_solar_systems_join" ON "solar_systems"."id" = "planet_types_solar_systems_join"."solar_system_id" INNER JOIN "planet_types" ON "planet_types"."id" = "planet_types_solar_systems_join"."planet_type_id" WHERE "planet_types"."life" = 't' AND "planet_types"."gravity" = 9.8
An easy solution that I found is that you can change your joins in your Planet class to
joins(Planet.joins(:planet_type).join_sql)
This will create an SQL string for the joins which will always include the correct table names and therefore should always be working no matter if you call the scope directly or use it in a merge. It's not that nice looking and may be a bit of a hack, but it's only a little more code and there's no need to change your associations.
I'm starting out with the whole (wonderful) idea of database associations in Rails but I'm having problems because I'm working with an existing database that does not conform to Rails standards and cannot figure out how to name the associations. There are a couple of similar posts, but I can't wrap my head around the naming for my particular situation which is as follows:
table book with book.formatId looks up values in book_format.id
So foreign key book.formatId
My models are named: Book and BookFormat (I read that you use camelCase when your tables are separated by underscore).
Under the Book model I have this:
has_one :bookFormat, :foreign_key => 'book_format.id' # not sure if this format table.field is correct or I have to use something else here. Also not sure about the bookFormat, should it be BookFormat or bookformat?
The BookFormat model has this:
belongs_to :book
But when I try to do
book = Book.first
book.bookFormat.empty?
I get an error of method not found for bookFormat. So obviously something's wrong, but I can't figure out where.
A second part of the question is the use of many to many relationships. Example:
Tables
book, book_subjects, book_subjects2title
book_subjects.id => book_subjects2title.pId
book.id => book_subjects2title.bookId
I'm reading the Beginning Rails 3 book from Apress (which is a great book) but it's not very clear on all this or I'm just not getting it.
Thanks.
Since the book stores the formatId on it, you should use belongs_to, and change the foreign key as such:
belongs_to :book_format, :class_name => 'BookFormat', :foreign_key => 'formatId'
For the table name, i did some quick searching, and found the following method: set_table_name
So you should be able to add it at the top of your model, like so:
class Book < ActiveRecord::Base
set_table_name 'book'
# the rest of book model code
end
class BookFormat < ActiveRecord::Base
set_table_name 'book_format'
# rest of book_format model code
end
Normally rails uses plural table names, so hence why you need to specify it there.
agmcleod put me on the right track, so here's the full answer in the hopes that this helps other people with similar problems:
I created the model with a different name for easier reading. So model Books will have:
class Books < ActiveRecord::Base
set_table_name 'bookpedia'
belongs_to :format, :foreign_key => 'formatId' # we need to specify the foreign key because it is not the rails default naming
has_many :author2title, :foreign_key => 'bookId'
has_many :author, :through => :author2title
end
model Format:
class Format < ActiveRecord::Base
set_table_name 'book_format'
has_many :books
end
Then an instance of the class will have the format method:
#book = Books.first
#book.format # Hardcover
For many to many relationships I'll paste the syntax here as well since that took me a while to figure out:
class Author < ActiveRecord::Base
set_table_name 'book_author'
has_many :author2title, :foreign_key => 'pId' # junction table
has_many :books, :through => :author2title # establishing the relationship through the junction table
end
This is the actual junction table:
class Author2title < ActiveRecord::Base
set_table_name 'book_author2title'
belongs_to :author, :foreign_key => 'pId' # foreign key needs to be here as well
belongs_to :books, :foreign_key => 'bookId'
end
The book model above has the necessary entries for this many to many relationship already in it.
If anyone needs clarification on this I'd be happy to oblige since I struggled for more than a day to figure this out so would be glad to be of help.
Cheers.
I have some issues with the polymorphic associations in Rails 3. My model looks like this:
class Address < ActiveRecord::Base
belongs_to :contactable, :polymorphic => true
end
class OrganisationUnit < ActiveRecord::Base
# some other associations
end
# Subclass of OrganisationUnit
class Company < OrganisationUnit
has_one :address, :as => :contactable
end
Now, when I want to get the Address of a Company, Rails generates the following SQL-Query:
SELECT `addresses`.* FROM `addresses` WHERE (`addresses`.contactable_id = 1021 AND `addresses`.contactable_type = 'OrganisationUnit') LIMIT 1
In my opinion it's wrong, because the contactable_type should be "Company".
Is there any way I can fix this or tell rails that OrganisationUnit is just an abstract base class?
The is an expected behavior. When you link a STI table to a polymorphic association, Rails stores the base class name rather than the inherited class names. The STI type conversion happens after the object lookup by id.