Models can associate in three main ways: one to many, one to one, and many to many.
This is tagged primarily in Ruby community. Models can associate in three main ways: one to many, one to one, and many to many.
Questions tagged [model-associations]
865 questions
94
votes
8 answers
Rails association with multiple foreign keys
I want to be able to use two columns on one table to define a relationship. So using a task app as an example.
Attempt 1:
class User < ActiveRecord::Base
has_many :tasks
end
class Task < ActiveRecord::Base
belongs_to :owner, class_name:…
JonathanSimmons
- 1,528
- 1
- 16
- 28
63
votes
8 answers
Validation failed Class must exist
I have been (hours) trouble with associations in Rails. I found a lot of similar problems, but I couldn't apply for my case:
City's class:
class City < ApplicationRecord
has_many :users
end
User's class:
class User < ApplicationRecord
…
Pedro Gabriel Lima
- 1,122
- 1
- 9
- 24
60
votes
4 answers
Aggregation vs Composition vs Association vs Direct Association
I am reviewing my knowledge in object-oriented programming. Under the relationship between classes topic, I have encountered some relationships which are a bit ambiguous to me.
I know dependency "uses-a" and inheritance "is-a" but I'm a bit…
steven0529
- 1,513
- 1
- 18
- 28
43
votes
2 answers
Same Model for Two belongs_to Associations
I have an model PointOfContact which has_many Systems. From the Systems side I want to identify the PointOfContact as either the technical_manager or project_manager (or both). While still only keeping the PointOfContact 1 time in the DB.
My attempt…
Ryan
- 6,432
- 7
- 40
- 54
43
votes
1 answer
Flask/SQLAlchemy - Difference between association model and association table for many-to-many relationship?
I started learning this stuff from the Flask Mega Tutorial. When he gets into Many-to-Many relationships, he creates an association table like this:
followers = db.Table('followers',
db.Column('follower_id', db.Integer,…
Chockomonkey
- 3,895
- 7
- 38
- 55
32
votes
4 answers
ExtJS 4: Models with Associations and Stores
Introduction
I'm facing an application design problem with the Ext.data.Model class in ExtJS. I will try to develop my ideas to a very common online store scenario here, so you can follow me. I would really appreciate any comments on my thoughts and…
Konrad Kleine
- 4,275
- 3
- 27
- 35
29
votes
2 answers
Rails Model, belongs to many
I'm having a hard time figuring out how to association one of my models with multiple of another.
As it is now, I have:
class ModelA < ActiveRecord::Base
has_many :model_b
end
class ModelB < ActiveRecord::Base
belongs_to…
ardavis
- 9,842
- 12
- 58
- 112
20
votes
4 answers
How do rails association methods work?
How do rails association methods work? Lets consider this example
class User < ActiveRecord::Base
has_many :articles
end
class Article < ActiveRecord::Base
belongs_to :user
end
Now I can do something like
@user =…
Chirantan
- 15,304
- 8
- 49
- 75
16
votes
3 answers
Sunspot rails: include associated models when calling .results
Let's say that I want to search for Events in my app.
When I display the results, I want to display who created the event, for instance.
Is there any way to add .includes(:user) somewhere, to avoid unnecessary queries (one for each event)? I can't…
Robin
- 21,667
- 10
- 62
- 85
16
votes
1 answer
Rails associations in namespaced models
I'm re-doing an app and migrating data from an old app. The some of the models names will be the same, though not all of them.
I'm writing a rake task to connect to the old database, read the records, do some stuff and write the result into a new…
John Small
- 942
- 2
- 12
- 21
14
votes
1 answer
Rails - execution sequence of after create callback & nested attributes
I have a simple set up of User and UserProfile model with User has_one :user_profile and UserProfile belongs_to :user.
But I am unable to wrap my head around how Rails defines execution order of after_create callback and…
prasvin
- 3,009
- 23
- 28
12
votes
4 answers
Access Nested Backbone Model Attributes from Mustache Template
I have one Backbone model which has an attribute that is a reference to another Backbone model. For example, a Person has a reference to an Address object.
Person
FirstName
LastName
Address
Street
City
State
Zip
These are…
Kevin
- 2,084
- 3
- 24
- 36
12
votes
1 answer
Rails 4: Difference between validates presence on id or association
If I have a 'belongs_to' association in a model, I'd like to know the notional difference between validating an association:
class Topping < ActiveRecord::Base
belongs_to :pancake
validates :pancake, presence: true
...
and…
A Fader Darkly
- 3,516
- 1
- 22
- 28
12
votes
0 answers
How do I show (collection) associations in Visual Studio's generated class diagrams?
Visual studio doesn't seem to recognize c++ STL classes properly when it comes to generating class diagrams.
There are two options when right-clicking class elements in the generated diagrams:
- Show as Association
- Show as Collection…
Jvlonden
- 155
- 2
- 8
11
votes
6 answers
extjs 4 XTemplate class associations
I'm testing out extjs 4 and I have stumbled upon something, I can't seem to figure out.
I have simple object association: Snapshot - hasMany -> Model
Now, I am trying to use XTemplate to show this association in View component, so I have my…
Greg
- 2,413
- 5
- 22
- 23