Adding data to a database in ruby

I am in quite the pickle , I think I overreach with my current ruby knowledge but I don't want to give up. I currently have a tweeter that can post and people can follow other people thanks to https://www.railstutorial.org/book/ . I do want to add hashtags to this tutorial tweeter. In order to do I created 2 tables since tweet and hashtag is a many to many relationship . The tables are :

  class CreateHashrelations < ActiveRecord::Migration
  def change
    create_table :hashrelations do |t|
      t.integer :tweet_id
      t.integer :hashtag_id

      t.timestamps null: false
    end
    add_index :hashrelations, [:tweet_id, :hashtag_id], unique: true
  end
end

which is the extra table you need to keep the keys of the tweet and hashtag . And the other table is the hashtag table where I have the id and the name of the hastag

class CreateHashtags < ActiveRecord::Migration
  def change
    create_table :hashtags do |t|
      t.string :name

      t.timestamps null: false
    end
  end
end

In the models I put the following relathipships:

class Hashtag < ActiveRecord::Base
    has_many :hashtagrelations, dependent: :destroy
    has_many :tweets, through: :hashtagrelations
    validates :name, presence: true
end

class Hashrelation < ActiveRecord::Base
    belongs_to :tweet
    belongs_to :hashtag
    validates :tweet_id, presence: true
    validates :hashtag_id, presence: true
end

class Tweet < ActiveRecord::Base
.....
  has_many :hashtagrelations, dependent: :destroy
  has_many :hashtags, through: :hashtagrelations
....

end

When a tweet is submited I save it and if it is saved I want to see if it has hashtags and if it does I want to add the necessary data in the Hashtagrelations and Hashtags tables. I try to do this this way :

class TweetsController < ApplicationController
......


  def create
    @tweet = current_user.tweets.build(tweet_params)
    if @tweet.save
      add_hashtags(@tweet)
      flash[:success] = "Tweet created!"
      redirect_to root_url
    else
      @feed_items = []
      render 'static_pages/home'
    end
  end

......

  private

........

    def add_hashtags(tweet)
      tweet.content.scan(/(?:\s|^)(?:#(?!(?:\d+|\w+?_|_\w+?)(?:\s|$)))(\w+)(?=\s|$)/){ |tag|
        newhash[:new] = tag
        @hashtag = Hashtag.new(new_hash[:new])
        @hashtag.save
        data[:new] = [tweet.id,@hashtag.id]
        @hashrel = Hashtagrel.new(data[:new])
        @hashrel.save
      }
    end

end

Which is not the right way. I tried to add the newhash and data because if I only did tag there I would get

When assigning attributes, you must pass a hash as an argument.

I realise that this is kind of a silly question but I have found no tutorial that teaches me how should I add this data to my tables. I would be grateful for your help