Rails table display and database design?

Question

I have two tables, Beacon belongs to Category and Category has many beacons, in beacon table, I add a foreign key: category_id, but when i want display in table, i need the category_name in the category table, now I use a stupid way as following:

...
<% @beacons.each do |beacon| %>
            <tr>
              <td><%= beacon.beacon_uuid %></td>
              <% @category_name = Category.find(beacon.category_id).category_name %>
              <td><%= @category_name %></td>
...

but when beacon data get bigger, request get bigger, how to change my code to defence this stupid question?can someone give me some suggestion or reference? Thanks a lot.

Hristo Georgiev · Accepted Answer · 2015-08-23 01:29:05Z

2

It sounds like you're referring to an N+1 query, wherein the number of queries executed is equal to the number of beacons + 1. If so, your queries look similar those below.

select beacons.* from beacons;
select categories.* from categories where categories.id = 1;
select categories.* from categories where categories.id = 2;
select categories.* from categories where categories.id = 3;

Assuming your beacon model has the belongs_to :category relation declared, this can be avoided by using includes to eager load the association in the controller

def index
  @beacons = Beacon.all.includes(:category)
end

The view can then be changed to take advantage of this, instead of pulling a fresh copy of the category from the database for each beacon

<%= beacon.category.category_name %>

edited Aug 23, 2015 at 1:29

Hristo Georgiev

2,5191 gold badge19 silver badges23 bronze badges

answered Aug 23, 2015 at 1:13

Alexa Y

1,8541 gold badge11 silver badges13 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Hristo Georgiev · Accepted Answer · 2015-08-23 01:19:32Z

0

There is a helper of the category and its attributes in the beacon itself.

In Rails, you can go both ways:

Category.beacons will return an array of all the beacons the category has and their attributes Beacon.category will return the attributes of its category.

Following the same logic, you just need this:

  <%= beacon.category.category_name %>

answered Aug 23, 2015 at 1:19

Hristo Georgiev

2,5191 gold badge19 silver badges23 bronze badges

1 Comment

John Over a year ago

Thanks...I tried, but in this case, when I have 10 beacon, it's still send 10 request to get category_name, this way is more clearly than before, but do the same thing... can I use only 1 request to get what I want?

Collectives™ on Stack Overflow

Rails table display and database design?

2 Answers 2

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related