ruby on rails - How to setup a one to many relationship? - Stack Overflow
so network has_many users and a user belongs_to network. Just add a network_id to users table if you still haven't and also since it's a. Finishing the simple blog implementation does require a one-to-many relationship between posts and comments. So first we need to add the. Using: Ruby , Rails Please note: I'm new to all this Ruby on Rails stuff, I'm posting these articles so if I make mistakes hopefully.
The relevant association declarations could look like this: For example, if you assign: If some that existed previously are now missing, then their join rows are automatically deleted.
Ruby on Rails one to many database relationships | Nick Swan's Blog
Automatic deletion of join models is direct, no destroy callbacks are triggered. For example, if a document has many sections, and a section has many paragraphs, you may sometimes want to get a simple collection of all paragraphs in the document. You could set that up this way: This association indicates that the declaring model can be matched with one instance of another model by proceeding through a third model.
For example, if each supplier has one account, and each account is associated with one account history, then the supplier model could look like this: For example, if your application includes assemblies and parts, with each assembly having many parts and each part appearing in many assemblies, you could declare the models this way: How do you know which is which? For example, it makes more sense to say that a supplier owns an account than that an account owns a supplier.
This suggests that the correct relationships are like this: In current versions of Rails, you can abstract away this implementation detail by using t. Rails offers two different ways to declare a many-to-many relationship between models. This makes the association indirectly, through a join model: With polymorphic associations, a model can belong to more than one other model, on a single association.
For example, you might have a picture model that belongs to either an employee model or a product model. Here's how this could be declared: From an instance of the Employee model, you can retrieve a collection of pictures: That object would just have the essential fields. To access the details, we could do something like Customer.
Automatic Building In this kind of scenario, we want every customer to have an associated Detail object.
In pseudocode, what we want to do is "create an attached Detail object whenever a Customer object is initialized". Automatic Destruction Given the current setup, when we destroy a Customer it is going to leave an orphaned Detail object in the database.
Instead, we want the child object destroyed automatically when the parent is destroyed.
Rails intro #2: One-to-many relationships
Instead, the parent object should present an interface to the child object. All of this is transparent from the outside. It breaks apart the array into a list of parameters, resulting in identical functionality to when we listed them all right in the call to delegate. One-to-Many One-to-many is the most common relationship in Rails.
Relationships - Jumpstart Lab Curriculum
One customer connects to many orders. One article connects to many comments. The relationship is asymmetric because the parent has many children, but the child has only one parent. In the Database At the database level it is very similar to a one-to-one: The parent record or row actually has no idea how many children are out there and only the child links back to the parent.