Relational database in ruby on rails

I'm trying to add a player to someone's personal team but I feel like it's not working because of the table design

ob264 is somewhat right:

#app/models/user.rb
Class User < ActiveRecord::Base
   has_many :teams
   has_many :players, through: :teams
end

#app/models/team.rb
Class Team < ActiveRecord::Base
   #fields id | user_id | other | team | details | created_at | updated_at
   belongs_to :user

   has_many :player_teams
   has_many :players, through: :player_teams
end

#app/models/player.rb
Class Player < ActiveRecord::Base
   #fields id | team_id | other | team | details | created_at | updated_at
   has_many :player_teams
   has_many :teams, through: :player_teams
end

#app/models/player_team.rb
Class PlayerTeam < ActiveRecord::Base
    belongs_to :team
    belongs_to :player
end

This will allow you to create the following setup:

#config/routes.rb
resources :teams #-> domain.com/teams/5/edit

#app/controllers/players_controller.rb
Class TeamsController < ApplicationController
   def edit
       @team = Team.find params[:id]
       @team.player_teams.build
   end

   def update
       @team = Team.find params[:id]
       @team.update(team_params)
   end

   private

   def team_params
      params.require(:team).permit(:team, :params, player_teams_attributes: [:player_id, :team_id])
   end
end

Although this will need tweaking, it will basically give you the ability to do this:

#app/views/teams/edit.html.erb
<%= form_for @team do |f| %>
   <%= f.fields_for :player_teams do |pt| %>
      <%= pf.collection_select :player_id, Player.all, :id, :name %> #-> adds a player to your team
   <% end %>
   <%= f.submit %>
<% end %>

--

ActiveRecord Associations

To answer your question more deeply, you have to appreciate the role of ActiveRecord associations that Rails uses. ActiveRecord is an "ORM" (Object Relational Mapper) layer for data-driven applications, allowing the application-layer to build associated objects together.

The difference here is that if you want to create "relations" / "associations" in your dataset, you have to do several important things:

1. You need to appreciate the role of foreign_keys in your data tables
2. You need to associate your models correctly
3. You need to work at object level

Firstly, you need to appreciate that ActiveRecord is not magic - it build objects based off the foreign_key in your data tables. This is typically a reference to the primary_key of the parent object:

This means that every time you build an association in Rails, you need to back it up with the data table foreign_keys it needs to find the respective data.

Secondly, you need to then ensure your models are associated correctly. The examples provided are a sufficient demonstration of how this should work (simple once you get your head around it!)

Thirdly, you need to the appreciate working at object level. This is very important - Rails (as it's built on Ruby) is an object orientated framework, meaning that everything you do is based around objects (which are constructed through the Models, from the database)

I am saying this because the way I built the methodology for you above is object orientated -- you're wanting to update a user's "Team" object by adding / removing players from the association. This is a very important pattern to realize within Rails - it will help you profusely if you appreciate how it works