Rails - check if record exists in has_many association

问题

I'm not sure if my question is worded correctly.

I have three models: User, Item, and UserItem.

user has_many :user_items
user has_many :items, through :user_items

item has_many :user_items
item has_many :users -> {uniq}, through :user_items
item belongs_to :user

user_item belongs_to :user
user_item belongs_to :item

I need a way to see if a user has an item to make if statements in my item views But here's the catch, user_items have enum status: [ :pending, approved]. So I need to see if a current_user has a certain :pending item.

For example when a user visits item1's view page I have the item_controller's show action declare @item = Item.find_by_id(params[:id]). But then what can I do with this @item to see if a user has this item?

回答1:

Try:

current_user.items.exists?(params[:id])

current_user.items.exists?(@item.id)

回答2:

But then what can I do with this @item to see if a user has this item?

I think what you are missing here is model methods. For example, if you added a method to the Item model called belongs_to_user_in_pending_state, you'd be able to call @item.belongs_to_user_in_pending_state(current_user) anywhere you need it.

def belongs_to_user_in_pending_state(user)
  if self.user_items.pending.select {|s| s.user == user}.count > 0 
    return true
  else
    return false
  end
end

回答3:

Extending @lei-liu's answer here. One can find if the record exists among the many or not, through: current_user.items.exists?(params[:id])

At the same time, exists? allows one to filter through the columns besides id, and also allows for more complicated conditions, like the following:

current_user.items.exists?('id > 3')
current_user.items.exists?(name: 'some_name')

回答4:

1) Add a scope to User_item class

scope :pending, -> {where status: 'pending'}

2) Use that scope in an instance method of Item class:

def is_pending_with_someone?
  self.user_items.pending.count > 0
end

Then you can use

if @item.is_pending_with_someone? 
  ...

来源：https://stackoverflow.com/questions/36490579/rails-check-if-record-exists-in-has-many-association

标签

ruby-on-rails

activerecord

associations

has-many