I have two models, Items and Calibrations. Items has many calibrations, meaning that every year the instruments have to be calibrated. Fields, date_calibration and date_expired, are located in the "calibrations" table. (Items: has_many :calibrations, calibration: belongs_to item)
I need list/show all the items that are expiring. I can list all the items without problem of course but, I don't know how to add date_expired to the list.
In the Items controller:
#items = Item.all.order("created_at DESC")
In the Index:
<% #items.each do |item| %>
<tr>
<td><%= item.cod %></td>
<td><%= item.number %></td>
<td><%= item.den_cont %></td>
<td><%= item.branch %></td>
<td><%= item.model %></td>
</tr>
<% end %>
I'm using Aptana and PostgreSQL version 9.1, Ruby 2.1 and Rails 4.1.
Can anyone of you suggest any solution or point me to the right direction?
UPDATE
What should I change to show the item using the sentence below..
Item_controller
Item.includes(:calibrations).where('calibrations.date_expired <= ?' , 2014/07/12)
Index
<% #items.each do |item| %>
Return undefined method each.
ALSO
Any idea on how to show a traffic light depending on how many days left to calibration_date ?? Tks again!
As long you have your relations properly defined in your models I do believe something similar to the following should do the trick!
Item.joins(:calibrations).where(date_expired <whatever condition>)
The equivalent SQL being:
SELECT Items.*
FROM Items
LEFT OUTER JOIN Calibrations
ON Calibrations.item_id = Items.item_id
WHERE date_expired <whatever condition>
With the equivalent SQL of the above statement being (using the includes method):
SELECT *
FROM Items
LEFT OUTER JOIN Calibrations
ON Calibrations.item_id = Items.item_id
WHERE date_expired <whatever condition>
Hope this helps!
Also, if you're not wanting to return any data related to the calibrations table (which it looks like this is the case), I would go with the joins method, however if you are, the includes method would be the way to go (http://tomdallimore.com/blog/includes-vs-joins-in-rails-when-and-where/)
Also, the following may be of interest: http://guides.rubyonrails.org/active_record_querying.html (particularly section 12)!
#items = Item.includes(:calibrations)
.where('calibrations.date_expired <= ?', some_date)
include will join the two tables and allow you to specify conditions on items based on columns from the calibrations table. I think that's what you wanted isn't it?
Related
There are multiple calculations I'd like to be able to perform on my database, all centred around a user id, but I don't know how to recombine them after.
Let's say I have three tables for User, Purchases, and DiscountUsage. I want to find the last date a user made a purchase and the total number of discounts used. I would run two separate commands:
User.joins(:purchases).group("users.id").select("users.id", "MAX(purchases.purchase_date)")
User.joins(:discount_usages).group("users.id").select("users.id", "COUNT(*)")
I want my final output to be one table though, joined on users.id, but the output from select isn't the right data type to work on with Rails functions. How can I represent that the users.id values from both calls are the same and thus join them based on those columns?
I assume a User may not have any purchases and not all purchases use discount codes.
However, you want a full listing of each user with their last purchase date and total discount usages over all purchases. You may need to use a right join.
Something like:
query = User.select('users.id AS user_id', 'MAX(purchases.purchase_date) AS last_purchase_date', 'COUNT(discount_usages.id) AS total_discount_usages')
.joins('LEFT JOIN purchases ON purchases.user_id = users.id')
.joins('LEFT JOIN discount_usages ON discount_usages.user_id = purchases.user_id')
.group('users.id')
.to_sql
Then in order to grab the fields you could use:
rows = ApplicationRecord.connection.select_all(query).to_hash
https://guides.rubyonrails.org/active_record_querying.html#select-all
This will give you an array of hashes with keys: 'user_id', 'last_purchase_date', 'total_discount_usages'.
...
<% rows.each do |row| %>
<% row.symbolize_keys! %>
<tr>
<td><%= row[:user_id] %></td>
<td><%= row[:last_purchase_date] %></td>
<td><%= row[:total_discount_usages] %></td>
<tr>
...
You can select aggregates from joined tables and access them in the model by using aliases:
#users = User.joins(:purchases, :discount_usages)
.select(
"users.id",
"MAX(purchases.purchase_date) AS latest_purchase",
"COUNT(discount_usages.*) AS discount_usages_count"
)
.group("users.id")
If you want to hydrate the other attributes of the records select users.* instead of just users.id.
<table>
<thead>
<tr>
<th>Id</th>
<th>Latest Purchase</th>
<th>Discount usages</th>
</tr>
</thead>
<tbody>
<% #users.each do |user| %>
<tr>
<td><%= user.id %></td>
<td><%= user.latest_purchase %></td>
<td><%= user.discount_usages_count %></td>
</tr>
<% end %>
</tbody>
</table>
I want my final output to be one table though, joined on users.id, but
the output from select isn't the right data type to work on with Rails
functions.
Not sure quite what you mean here. This example will return a collection of user records just like a normal query.
If you want a "raw" result with just an array of arrays use .pluck instead of .select.
I have a model Schools and a model PerformanceStats.
PerformanceStat
belongs_to :school
School
has_one :performance_stat
the index page for PerformanceStat shows all 2,000 performance stats, and also the school.name, school.score, and school.city, and I need access to the school.id and school.slug.
Controller:
def index
#performance_stats=PerformanceStat.all
end
My view code:
<tbody>
<% #performance_stats.each do |stat| %>
<% school = School.find(stat.school_id)%>
<tr>
<td><%= link_to school.name, school_path(city: school.city.parameterize.truncate(80, omission: ''), slug: school.slug) %></td>
<td><%= number_with_precision(school.score, precision: 2)%></td>
then the view goes on to display the performance stats.
This view load very slowly....10-20 seconds. How can I speed things up? I've tried PerformanceStats.scoped, and plucking school stats and selecting from an array, but these don't seem to help. Is there a way for me to access the school attributes without finding a School for every PerformanceStat? I believe the School.find bit is slowing things down considerably.
I have indexes on :school_id in PerformanceStat, and :score, :slug in the School model.
UPDATE:
The suggestion in the selected answer to add a cache resulted in this line of code in the index action of the SchoolsController:
fresh_when etag: #performance_stats
The load time dropped to 18ms. This solution works great for me because the content of the index action does not change often. This data gets updated once a year. This link has other suggested cache solutions for data that changes frequently.
PerformanceStat.all is a heavy query if you've a lot of data in this table and it'll be finding school for each performance stat.
What I can understand from your code is that you're facing (N + 1) problem over here.
NOTE: you should not fire queries from your views or helpers and let the controller do all the action.
For instance in your code:
<% #performance_stats.each do |stat| %>
<% school = School.find(stat.school_id)%> <- #THIS IS WRONG & LET THE ASSOCIATIONS DO ALL THE ACTION ON ITS OWN
<tr>
<td><%= link_to school.name, school_path(city: school.city.parameterize.truncate(80, omission: ''), slug: school.slug) %></td>
<td><%= number_with_precision(school.score, precision: 2)%></td>
you can use includes, PerformanceStat.includes(:school) it will fetch all the schools for each PerformanceStat.
your controller code should be:
#performance_stats = PerformanceStat.includes(:school)
instead of : #performance_stats = PerformanceStat.all
and your view code will now be:
<% #performance_stats.each do |stat| %>
<% school = stat.school %> #make sure all stats have a school assigned to them otherwise you can put a check below whether the school is nil or not
<tr>
<td><%= link_to school.name, school_path(city: school.city.parameterize.truncate(80, omission: ''), slug: school.slug) %></td>
<td><%= number_with_precision(school.score, precision: 2)%></td>
Quite a few things here. First of all change your controller method to this one, otherwise you will run into n+1 queries
def index
#performance_stats=PerformanceStat.includes(:school)
end
Since you have eagerly loaded the school, now you can access it directly in your view as
<% stat.school %>
Secondly loading almost 2000 records in one go is not optimal at all, it's gonna take a while to load all records. For this you must add pagination by using following gems
kaminari
will_paginate
This is related to this previously asked question
I have a has_and_belongs_to_many in place between Product and Supplier.
In my view I use:
<td><%= product.suppliers.map {|supplier| supplier.NAME }.join(', ') %></td>
To show list of suppliers comma separated on each row for each product in my table.
I now need to show the same list on invoices index view. Invoices table has a column PRODUCT. I have already set belongs_to :product on Invoice model.
I tried in my invoices index view:
<td><%= invoice.product.suppliers.map {|supplier| product.supplier.NAME }.join(', ') %></td>
but it returns
error undefined local variable or method `product'
Why isn't that working? How can I fix it? Thanks in advance.
you build wrong .map, try
invoice.product.suppliers.pluck(:NAME).join(', ')
BTW
it's bad practice use logic in view, you should move your logic to models, and in view use something like:
<%= invoice.suppliers_names %>
what should return # => 'Name_1, Name_2, etc'
I get that one should not ping the database in the view... but wondering about the right solution. In one of my views, I need to pull info on an #order, it's child items, and also Amount, another model, based on each child item. Something like this:
<% #order.items.each do |item| %>
<td><%= item.name %></td>
<td><%= Refund.where(item_id:item.id).first.amount %></td>
<td><%= Amount.where(item_id: item.id).first.amount %></td>
<% end %>
For the sake of avoiding the db hits in the view, the only solution I've thought of is to create a huge hash of all the relevant data in the controller, which is then accessed from the view. So it would be something like this:
# controller (writing quickly, code may not be totally right, hopefully you get gist
data = Hash.new
data["items"] = []
#order.items.each do |item|
item_hash = {
"name" => item.name,
"amount" => Amount.where(item_id: item.id).first.amount,
"refund" => Refund.where(item_id:item.id).first.amount
}
data["items"] << item_hash
end
# view code
<% data["items"].each do |item| %>
<td><%= item["name"] %></td>
<td><%= item["refund"] %></td>
<td><%= item["amount"] %></td>
<% end %>
And I know SO hates this type of question... but I really need to know... is that the best solution? Or are there are best practices? The reason I ask is because it seems very clean in the view, but very bulky in the controller, and also it gets quite unwieldy when you have a much more complex set of nested tables, which is what I actually have (i.e., the data hash would be quite funky to put together)
First of I would use associations between item and the 2 other classes, so that you can do
item.refund
item.amount
Instead of Refund.where(...). You could further define methods such as
def refund_amount
refund.amount
end
And similarly for the other one (and hopefully come up with a better name than amount_amount.
This keeps both your view and controller clean but it won't be any faster. So far all of the approaches involve running 2 database queries per item which is the real issue as far as I'm concerned - whether those excess queries happen in the view or the controller is of lesser concern.
However you can avoid this with Active Record's include mechanism:
Item.include(:amount,:refund).where("your conditions here")
Will load the named associations in bulk rather than loaded them one at a time as each item is accessed.
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.
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 %>
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 %>