Qiita has many attractive articles, so I tend to refer to many articles. However, since there are various ways of writing depending on the article, if you refer to multiple articles without understanding the contents, it tends to cause an error. Therefore, when implementing one function, only one article should be referred to.
For example, if you want to create a DM function https://qiita.com/tenitiumai/items/3d9466d7a24197f690bb　 Let's assume that you referred to.
model/message.rb
class Message < ApplicationRecord
belongs_to :user
belongs_to :room
end
Suppose you had code like this in user.rb in the above article. However, because I referred to another article, in reality
model/message.rb
class User < ApplicationRecord
validate :messages, presence: true
has_many :messages, dependent: :destroy
has_many :entries, dependent: :destroy
end
Suppose it was described as.
Even if this one does not work, if you keep writing multiple unnecessary codes, it will cause an unexpected error. It is not necessary to bind messages with validate here. This is because it is strange to write code that always requests a message even though it is a message model.
models/user.rb
has_many :comments, dependent: :destroy
has_many :entries, dependent: :destroy
has_many :messages, dependent: :destroy
has_many :rooms, dependent: :destroy
This also has an unnecessary part. In the DM function, user arrives at room via the intermediate table entries, so there is no need to write has_many: rooms. As mentioned above, when the code piles up unnecessarily You will get an error like this. In particular, the model part is the basis for creating controllers and acitons, so it is safe to refrain from writing unnecessary code on the model page as much as possible.
This error is caused by not understanding the basics properly. It's easy for beginners to do it, so it's safe to keep it as one as possible when referring to the article (if you can understand the basics, you can refer to more than one ...).
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