Narrow elements in a join table by a dropdown menu. (Rails 4) - ruby-on-rails

Question

for one of my join tables, I'd like to filter results based on a dropdown menu selection. Before I explain further, I will provide the relevant code.
I have 3 models in question:
class Scoreboard
has_many :teams, has_many :team_matches
end
class Team
belongs_to Scoreboard
#self reference with the teams to create team_matches.
has_many :first_team, class_name: "TeamMatch", foreign_key: "team_a_id", dependent: :destroy
has_many :team_a, through: :first_team, source: :team_a
has_many :second_team, class_name: "TeamMatch", foreign_key: "team_b_id", dependent: :destroy
has_many :team_b, through: :second_teams, source: :team_b
end
And the final Model which is a join table of teams:
class Team_Match
belongs_to :team_a, class_name: "Team"
belongs_to :team_b, class_name: "Team"
belongs_to :scoreboard
end
Team Matches Controller Code for the Index View:
class TeamMatchesController < ApplicationController
require 'will_paginate/array'
def index
#selected = true
#scoreboard = Scoreboard.find(params[:scoreboard_id])
#teams = #scoreboard.teams
#matches = #scoreboard.team_matches.order("match_date DESC").paginate(page: params[:page], per_page: 5)
end
end
The Index Page View:
<h2 class="team-matches-header">TEAM MATCHES</h2>
<% if manager_or_owner?(#scoreboard, current_user) %>
<%= link_to "Add Matches", new_scoreboard_team_match_path(#scoreboard), class: "btn btn-primary" %>
<%= link_to "Clear Matches", deletematches_scoreboard_path(#scoreboard),method: :delete, class: "btn btn-danger", :data => {:confirm => "Are you absolutely sure you want to delete all matches?"} %>
<% end %>
<%= form_tag(scoreboard_team_matches_path, :method => "get", id: "match-search-form", autocomplete: "off") do %>
<div class="row new-member-field">
<div class="col-xs-12 col-sm-6">
<%= select_tag "teams", options_from_collection_for_select(#teams, "id", "name"), prompt: "Select something", class:"form-control" %>
<%= submit_tag 'Filter' %>
</div>
</div>
<% end %>
<div class="match-list">
<%= render 'match_list' %>
</div>
The Match List Partial
<% if #matches.present? %>
<% #matches.each do |game| %>
<div class="row match-div clearfix" id="match_<%= game.id %>">
<div class="col-xs-12 match-column">
<div class="facing-teams">
<div class="first-team">
<%= game.team_a.name %>
</div>
<div class="second-team">
<%= game.team_b.name %>
</div>
</div>
</div>
</div>
<% end %>
<% end %>
<div class="row">
<div class="col-xs-12 new-member-pages">
<%= will_paginate #matches %>
</div>
</div>
So far on the team matches index page, I have been able to put a dropdown menu selection with a list of teams. The trouble I'm having is how to make it functional. Upon submission of a team from the dropdown selection, I would like to display a list of Match objects(#matches) whose :team_a_id or :team_b_id matches the selected Team's id. How would I go about doing that?

Answer 1

I would use scopes to achieve what you want. Scopes are reusable filters that you can apply to an association to find exactly the records that you want.
This is how you would create a scope that finds the matches for a particular team:
class Team_Match
scope :has_team, ->(team_id) {
team_a = arel_table[:team_a_id].eq(team_id)
team_b = arel_table[:team_b_id].eq(team_id)
team_a_or_b = team_a.or(team_b)
where(team_a_or_b)
}
end
This uses arel (which ActiveRecord uses under the hood to create SQL queries) in order to find a match in either the team_a_id or team_b_id columns. If you have no idea what's going on with the above code, take a quick trip to Mastering AR and Arel to get up to speed.
You use the scope like this:
matches = Team_Match.has_team(team_id)
You can also use the scope on any relationship that joins to Team_Match:
matches = #scoreboard.team_matches.has_team(team_id)
Scopes can also be chained together:
matches = #scoreboard.team_matches.has_team(team_id).where(match_date: today)
The scope allows you to pass in the team id from the select box to find the matches:
def index
#selected = true
#scoreboard = Scoreboard.find(params[:scoreboard_id])
#teams = #scoreboard.teams
#matches = #scoreboard.team_matches.order("match_date DESC")
#matches = #matches.paginate(page: params[:page], per_page: 5)
# we apply the scope (if present) to only show the matches for the selected team
if (team_id = params[:selected_team_id])
#matches = #matches.has_team(team_id)
end
end
The only change you would need to make to the above code is working out what the actual name is of the param variable that holds the selected team id.