Ruby and Rail link two tables?

Question

Ruby on Rails

Hey, I'm making categories. But I just can not understand one chip.
Below is what I do.
As you can see, I have created a posts_category table for the categories.
And on the posts/new page,
I get an error about the absence of the categories table in the database.
Where does it come from? How to make him eat exactly posts_category?

class CreatePostsCategory < ActiveRecord::Migration
  def change
    create_table :posts_category do |t|
      t.string :name
      t.integer :user_id

      t.timestamps
    end
  end
end

class CreatePosts < ActiveRecord::Migration
  def change
    create_table :posts do |t|
      t.integer :user_id
      t.string :title
      t.text :description
      t.belongs_to :category

      t.timestamps
    end
  end
end

class Posts < ActiveRecord::Base
  belongs_to :category
end

To template

<%= f.collection_select :category_id, Category.order(:name), :id, :name %>

Answer 1

according to rails convention there can't be a label named posts_category
it can be post_categories - when one category has many posts, 1-to-many relationship and there can be categories and posts_categories tables - many-to-many relationship
That is, in your case, there should most likely be a post_categories label and belongs_to :post_category everywhere

Answer 2

Try replacing t.belongs_to :category with t.belongs_to :category, references: :posts_categories.
Naturally, you will have to specify the correct foreign_key and class_name in the models themselves, otherwise it will not work (despite the successful migration). Remember that Rails is Convention Over Configuration, deviating from conventions - be kind enough to specify a bunch of parameters (which you might not even know existed).