I'm still learning Ruby, and get caught up in alot of the 'magic', wanting to better understand what is actually happening, and making sure that I understand what it is doing.
I've got a user, and each user has entries.
In my user class, I have
has_many :entries
and in my entries class I have
belongs_to :user
I was expecting that the entries table would have a column for users, but I'm not seeing that when I 'describe' the database.
How do I know, or how does Rails know which user the entry is connected to? Or do I need to create a field myself to do that?
It seems strange to me that we have all these 'belongs_to', etc. yet it isn't explicit how that connection is made.
This is a common misconception. Associations do not create the database tables for you. Instead, you have to create them yourself. What you need to be careful of, is that an Entry model would have a user_id field, in order for the association to fully work. I truly would not want to advertise or anything, but i have created a blog post that can help you quite a lot i think :
http://www.codercaste.com/2011/02/06/rails-association-in-plain-english-what-i-wish-i-had-known-before-i-started/
Related
How do I associate two entries in a database that are connected through a many-to-many relationship in Rails?
I'm trying to associate Users and Issues for an issue tracker. I'm using has_and_belongs_to_many, not :through. I have a :user_id and :issue_id available to me, but there doesn't seem to be User.issues.find(id) or Issue.users.find(id) available to me. I have a route post "/", to: "home#create". I'm trying to make a create method in home_controller.rb.
From the look of it you're calling the method on the User class and not an instance.
If you want to get the issues connected to a user you need to fetch the user first:
User.find(id).issues
If you want to add a record to the association you can use the shovel method or any of the methods generated by the association macro:
User.find(id).issues << Issue.find(3)
User.find(id).issues.push(Issue.find(3))
User.find(id).issue_ids = [1, 2, 3]
Besides that you have a smattering of naming issues in your schema. Use snake_case everywhere in your database schema unless you have a good reason why you want to break the conventions and feel like explicitly configuring table and foreign key names.
I would also really question if you really want to use has_and_belongs_to_many. It should only really be used if you can't foresee that you ever will need to add additional attributes to the join table or never need to query the table directly - it seems pretty unrealistic that that would be true in an issue tracker. You want has_many through: - pretty much always.
I have a route post "/", to: "home#create". I'm trying to make a
create method in home_controller.rb.
Don't throw everything into a junk drawer controller. Think about your app in terms of resources that can be CRUD:ed and create controllers that handle just that resource. You should think about what the relation between a user and an issue is in your domain and how you can model it as an actual entity in the domain logic instead of just plumbing.
Maybe all I need to do is direct you to Rails Guides: Active Record Associations.
There is neither of these
User.issues.find(id)
Issue.users.find(id)
because when you are finding an issue or user by id, you don't use the association. Instead use these:
Issues.find(id)
Users.find(id)
Since the :id is unique this will work and should be what you want.
The only time you want to query issues or users using the association will be when you have the data for the other end of the relationship.
user = User.find(user_id)
issue = user.issues.where(id: issue_id)
Since the :id field is unique, this is the same as Issues.find(id). However if you want to get a collection of a user's issues with some other data, you can put the condition for that data in the where.
You can create an issue for a user this way:
user = User.find(user_id)
issue = User.issues.create( ... )
I have an app where I have three models. I have leads and customers which are very similar (but different enough that they warranted their own models). Then I have a polymorphic model called "Interactions" which has an interactionable_id and an interactionable_type (which would, of course, be either 'customer' or 'lead').
I recently tried to build a method that would migrate an interaction from a lead to a customer (when a lead is upgraded to being a customer).
I wanted to keep my code lean, and in order to keep my method simple, I decided to simply update the attributes of the interaction so that the interactionable_id and interactionable_type would change to the customer's id and to "Customer" respectively.
I tried many various methods of doing this, and the only thing that I could get to update was the interactionable_type. The interactionable_id would not change, no matter what I tried. I tried putting in a static number (rather than customer.id). I tried update_attributes and I tried to update the attributes individually and then save it. Also, I did have :interactionable_id in the attr_accessible list.
I got this to work because I decided to approach the problem slightly differently, but I could not find any answers out there as to exactly why this was happening.
I was just wondering if anyone knew why this might be. Is there some sort of a lock on polymorphic association ids? Why couldn't I change the association?
This should work
interaction.interactionable = customer
interaction.save
If model User has_one Profile, is there a simple way to find all users who have no profile without a custom query (eg NOT User.where('profile_id IS NULL')) or processing it in the app?
Since the association between User and Profile is already known to Rails I don't want to restate it. I want to keep this DRY. The actual connection between the models is more complex than this simple example (uses keys and class name) and may change in the future.
As #tadman & #antonk already said, you probably want to use scope:
scope :without_profile, where(profile_id: nil)
EDIT:
To answer #David Mauricio's question: you could use it by calling User.without_profile, to return the AR association of all users with a nil :profile_id.
#DriverDan : then I'm really unsure what you're asking for. Ask another question with more details, and we can try to answer it!
Here is my situation. I have model called Account. An account can have one or more contracts. The problem is that i'm dealing with a legacy application and each account's contracts are stored in a different database.
Example:
Account 1's contract are in account1_db.contracts.
Account 2's contract are in account2_db.contracts.
The database name is a field stored in accounts table.
How can i make rails association work with this?
This is a legacy PHP application and i simply can't change it to store everything in one table. I need to make it work somehow.
I tried this, but it didn't worked:
has_many :contracts, :conditions => [lambda{ Contract.set_table_name(self.database + '.contracts'); return '1' }]
Any ideas?
Why isn't database migration an option?
You're approaching this the wrong way. You want the two systems in your integration to be loosely coupled. By trying to get the two associated, you're creating an array of interdependencies that will later come around to backstab you. The approach you are trying creates tight coupling and reduces cohesion.
But, to directly answer your question, see below. Once again, I don't recommend implementing what I say below, but it would technically be a solution.
The first thing is that rails associations work only with foreign key. In fact, all database associations work this way. There isn't a ActiveRecord method of association without foreign keys as it defies what it means to associate two objects.
So you're not going to get it done with a has_many association. Instead, I would just manually create a function on your Contract model that simulates a has_many association.
class Account
memoize :contracts
def contracts
# Load from other database in here
end
def contracts=
# Push to other database in here
end
end
I've come across an oddity in ActiveRecord's #relationship_ids method (that's added automatically when you declare 'has_many'), which saves immediately for existing records, which is causing me some issues, and I wonder if anyone had any useful advice.
I'm running Rails 2.3.5.
Consider this simple scenario, where an article has_many tags, say:
a = Article.first
a.name = "New Name" # No save yet
a.author_id = 1 # No save yet
a.tag_ids = [1,2,3] # These changes are saved to the database
# immediately, even if I don't subsequently
# call 'a.save'
This seems surprising to me. It's specifically causing problems whilst trying to build a preview facility - I want to update a bunch of attributes and then preview the article without saving it - but in this instance the tag changes do get saved, even though no other fields do.
(Of possible relevance is that if 'a' is a new article, rather than an existing one, things behave as I'd expect - nothing is saved until I call 'a.save')
I have a fairly nasty workaround - I can override the tag_ids= method in my model to instead populate an instance variable, and actually save the related models in a before_save callback.
But I'd love to know of a simpler way than me having to do this for every model with a has_many relationship I'd like to create a preview facility for.
Does anyone have any fixes/workarounds/general advice? Thanks!
There's a reason things are this way. It's called foreign keys. In a has many relationship, the information that links to the model that has many is stored outside of that model as a foreign key.
As in Articles, has many tags. The information that links a tag to an article is stored either in the tags table or in a join table. When you call save on an article you're only saving the article.
Active record modifies those other records immediately. Except in the case where you're working with a new article that hasn't been saved yet. Rails will delay creating/updating the associated records if it doesn't know which id to place in the foreign key.
However, if you're modifying existing records, the solution you've decided on is really all that you can do. There's an even uglier hack using accepts_nested_attributes_for, but it's really not worth the effort.
If you're looking to add this behaviour to many models but not all models, you might want to consider writing a simple plugin to redefine the assigment the method you need and add the call back in a single class method call. Have a look at the source of something like acts_as_audited to see how it's done.
If you're looking to add this behaviour to all models, you can probably write a wrapper for has_many to do that.