问题
I just finished the Michael Hartl Rails Tutorial. Trying to make something of my own.
I am having trouble with getting rails to understand the relationships I'm trying to create. I'll try to simplify this as much as possible. A tree with branches, twigs and leaves would be apt, but...
I'll use the parent child format as an example. So naturally I have users, and let's say users create families.
So:
Class User < ActiveRecord::Base
has_many :families
has_many :parents
has_many :children
end
Class Family < ActiveRecord::Base
belongs_to :user
has_many :parents
end
Class Parent < ActiveRecord::Base
belongs_to: :user
belongs_to: :family
has_many: :children
end
Class Child < ActiveRecord::Base
belongs_to :user
belongs_to :parent
end
As you can see, I want a child to belong to the parent which belongs to the family, but the child itself does not belong to a family except through the parent. Sad if this weren't a metaphor, but true in this particular case. ;)
I have tried under Parent:
has_many :children, through: :parent
and
has_many :children, through: :family
But that didn't work.
When I try to use:
User.family.new
or
User.child.new
...it says the method doesn't exist. I take that to mean that it isn't understanding the relationships.
What am I doing wrong?
If it's relevant, the only thing in the family, parent, child tables for now are these columns:
t.string :content
t.integer :user_id
回答1:
You don't have these methods:
User.family.new
User.child.new
When you define has_many association, you just have these methods to create new object associated:
collection.build(attributes = {}, …)
collection.create(attributes = {})
Follow Rails guide:
collection is replaced with the symbol passed as the first argument to has_many
You can look at this has_many association reference for more info.
So, If User want create new family or child, you need to use these methods:
user = User.create(name: "ABC") # create new user and save to database.
user.families.build # create new family belongs to user
user.children.build # create new children belongs to user
user.families.create # create new family belongs to user and save it to database.
user.children.create # create new child belongs to user and save it to database.
If you want to get children belongs to parent which belongs to family, you can modify your association:
Class Family < ActiveRecord::Base
belongs_to :user
has_many :parents
has_many :children, through: :parents # Get children through parents
end
Class Parent < ActiveRecord::Base
belongs_to: :user
belongs_to: :family
has_many: :children
end
Class Child < ActiveRecord::Base
belongs_to :user
belongs_to :parent
end
Now, you can get all children belongs to parents which belongs to a family ( I suppost family have id = 1) with:
f = Family.find(1) # Find a family with id = 1
f.children # Get all children in family.
来源：https://stackoverflow.com/questions/13614063/rails-belongs-to-multiple-methods