I have a model, lets say Ad, which I plan to fetch 2 datasets from, then merge them into 1. Is this possible:
ads = Ad.where(etc).limit(5)
if ads.length < 5
merge = Ad.where(etc).limit(remainder)
// merge both here
ActiveRecord allows you to do chaining. Try this out, it will execute only one query.
ads = Ad.where(etc).limit(5)
ads = ads.where(etc).limit(remainder)
But in your case, you call the length method so it will execute two queries. However, you can still do chaining. User count method is better than length method because count will send a COUNT(*) to your database (faster). length will load all records based on the where conditions and do a count on array (slower).
ads = Ad.where(etc).limit(5)
if ads.count < 5
ads = ads.where(etc).limit(remainder)
end
Related
I'm working with a Rails 5 API. I have a simple model of a store, with:
order has_one checkout
checkout has_one transaction
checkout belong_to order
transactions belongs_to checkout
checkout has_many items
1 1 1 1
order -----> checkout ------> transaction
1 *
------> item
I want and endpoint that given an amount of the transactions, it returns a json with data from the transactions.
I have this code that works but it takes a lot of time. For example, a month worth of transactions it's taking 1 minute.
def get_all_transactions
transactions = Transaction.where.not(status: 'error')
data = transactions.map do |transaction|
checkout = transaction.checkout
order = Order.find(checkout.order_id)
checkout.items.map do |item|
{
checkout_id: checkout.id,
order_id: checkout.order_id,
item_id: item.id,
client_name: checkout.client.full_name,
order_created_at: order.created_at
}
end
end
data.flatten!
end
How can I improve this code to have a better performance?
I have also notice that removing for example, the checkout.client.full_name it takes like 20 seconds off.
With full_name being in the client model:
def full_name
"#{first_name} #{last_name}".strip
end
Why would that take 20 seconds?
The problems here is that you have layers upon layers of N+1 queries. Every time you call an association that hasn't been eager loaded you're causing another round trip to the database. Even if you add includes or eager_loads then the next issue is that you're loading tons off data of the tables that you're not using and creating model instances in memory just to use a single attribute off them.
The most efficient way to do this is most likely going to be to simply perform a join and just select the columns you're actually interested in:
sql = Item.joins(order: { checkout: :client })
.select(
Item.arel_table[:id].as('item_id'),
Order.arel_table[:id].as('order_id'),
"TRIM(CONCAT(clients.first_name, ' ', clients.last_name)) AS client_name",
Order.arel_table[:created_at ].as('order_created_at')
)
result = Item.connection.select_all(sql.arel).map(&:to_h)
This avoids creating entire models instances in memory in multiple levels when all you need is a single column.
However its very unclear what the actual expected result is here or why you're basing the query off the Transaction model when you're actually getting an array of items in the result.
I have 2 tables contractPoint and contractPointHistory
ContractPointHistory
ContractPoint
I would like to get contractPoint where point will be subtracted by pointChange. For example: ContractPoint -> id: 3, point: 5
ContractPointHistory has contractPointId: 3 and pointChange: -5. So after manipulating point in contractPoint should be 0
I wrote this code, but it works just for getRawMany(), not for getMany()
const contractPoints = await getRepository(ContractPoint).createQueryBuilder('contractPoint')
.addSelect('"contractPoint".point + COALESCE((SELECT SUM(cpHistory.point_change) FROM contract_point_history AS cpHistory WHERE cpHistory.contract_point_id = contractPoint.id), 0) AS points')
.andWhere('EXTRACT(YEAR FROM contractPoint.validFrom) = :year', { year })
.andWhere('contractPoint.contractId = :contractId', { contractId })
.orderBy('contractPoint.grantedAt', OrderByDirection.Desc)
.getMany();
The method getMany can be used to select all attributes of an entity. However, if one wants to select some specific attributes of an entity then one needs to use getRawMany.
As per the documentation -
There are two types of results you can get using select query builder:
entities or raw results. Most of the time, you need to select real
entities from your database, for example, users. For this purpose, you
use getOne and getMany. But sometimes you need to select some specific
data, let's say the sum of all user photos. This data is not an
entity, it's called raw data. To get raw data, you use getRawOne and
getRawMany
From this, we can conclude that the query which you want to generate can not be made using getMany method.
I am currently trying to filter out from selected data in Ruby on Rails those where the attribute "amount_available" is greater than zero. This would be no problem via #events.where(ticket_categories.amount_available > 0), but ticket_categories is an array with not a fixed length, because there can be multiple categories. How can you easily iterate through the array in the where clause and do this comparison?
I only need the events in the output where at least one associated category has the amount_available > 0.
This is my code:
#upcoming_events = #events.where("date >=?", Date.current)
#available_events = #upcoming_events.where(ticket_categories[0].amount_available > 0)
json_response(#available_events)
You can chain where conditions and you can add conditions that are based on associated models with joins:
available_events = #events
.where('date >= ?', Date.current)
.joins(:ticket_categories).where('ticket_categories.amount > 0')
.group(:id)
render json: available_events
Note: Database joins might return duplicate records (depending on your database structure and the condition) therefore the need to group the result set by id.
It is only a representation because the Events table is linked to TicketCategories via has_many. I use PostgresSQL and could now solve it with the following code:
#upcoming_events = #close_events.where("date >=?", Date.current)
available_events = []
#upcoming_events.each do |event|
event.ticket_categories.each do|category|
if category.amount_available > 0
available_events.push(event)
break;
end
end
end
render json: available_events
I am trying to construct a site which ranks performances for a selection of athletes in a particular event - I have previously posted a question which received a few good responses which me to identify the key problem with my code currently.
I have 2 models - Athlete and Result (Athlete HAS MANY Results)
Each athlete can have a number of recorded times for a particular event, i want to identify the quickest time for each athlete and rank these quickest times across all athletes.
I use the following code:
<% #filtered_names = Result.where(:event_name => params[:justevent]).joins(:athlete).order('performance_time_hours ASC').order('performance_time_mins ASC').order('performance_time_secs ASC').order('performance_time_msecs ASC') %>
This successfully ranks ALL the results across ALL athletes for the event (i.e. one athlete can appear a number of times in different places depending on the times they have recorded).
I now wish to just pull out the best result for each athlete and include them in the rankings. I can select the time corresponding to the best result using:
<% #currentathleteperformance = Result.where(:event_name => params[:justevent]).where(:athlete_id => filtered_name.athlete_id).order('performance_time_hours ASC').order('performance_time_mins ASC').order('performance_time_secs ASC').order('performance_time_msecs ASC').first() %>
However, my problem comes when I try to identify the distinct athlete names listed in #filtered_names. I tried using <% #filtered_names = #filtered_names.select('distinct athlete_id') %> but this doesn't behave how I expected it to and on occasions it gets the rankings in the wrong order.
I have discovered that as it stands my code essentially looks for a difference between the distinct athlete results, starting with the hours time and progressing through to mins, secs and msec. As soon as it has found a difference between a result for each of the distinct athletes it orders them accordingly.
For example, if I have 2 athletes:
Time for Athlete 1 = 0:0:10:5
Time for Athlete 2 = 0:0:10:3
This will yield the order, Athlete 2, Athlete1
However, if i have:
Time for Athlete 1 = 0:0:10:5
Time for Athlete 2 = 0:0:10:3
Time for Athlete 2 = 0:1:11:5
Then the order is given as Athlete 1, Athlete 2 as the first difference is in the mins digit and Athlete 2 is slower...
Can anyone suggest a way to get around this problem and essentially go down the entries in #filtered_names pulling out each name the first time it appears (i.e. keeping the names in the order they first appear in #filtered_names
Thanks for your time
If you're on Ruby 1.9.2+, you can use Array#uniq and pass a block specifying how to determine uniqueness. For example:
#unique_results = #filtered_names.uniq { |result| result.athlete_id }
That should return only one result per athlete, and that one result should be the first in the array, which in turn will be the quickest time since you've already ordered the results.
One caveat: #filtered_names might still be an ActiveRecord::Relation, which has its own #uniq method. You may first need to call #all to return an Array of the results:
#unique_results = #filtered_names.all.uniq { ... }
You should use DB to perform the max calculation, not the ruby code. Add a new column to the results table called total_time_in_msecs and set the value for it every time you change the Results table.
class Result < ActiveRecord::Base
before_save :init_data
def init_data
self.total_time_in_msecs = performance_time_hours * MSEC_IN_HOUR +
performance_time_mins * MSEC_IN_MIN +
performance_time_secs * MSEC_IN_SEC +
performance_time_msecs
end
MSEC_IN_SEC = 1000
MSEC_IN_MIN = 60 * MSEC_IN_SEC
MSEC_IN_HOUR = 60 * MSEC_IN_MIN
end
Now you can write your query as follows:
athletes = Athlete.joins(:results).
select("athletes.id,athletes.name,max(results.total_time_in_msecs) best_time").
where("results.event_name = ?", params[:justevent])
group("athletes.id, athletes.name").
orde("best_time DESC")
athletes.first.best_time # prints a number
Write a simple helper to break down the the number time parts:
def human_time time_in_msecs
"%d:%02d:%02d:%03d" %
[Result::MSEC_IN_HOUR, Result::MSEC_IN_MIN,
Result::MSEC_IN_SEC, 1 ].map do |interval|
r = time_in_msecs/interval
time_in_msecs = time_in_msecs % interval
r
end
end
Use the helper in your views to display the broken down time.
I have a database table called Event which in CakePHP has its relationships coded to like so:
var $belongsTo = array('Sport');
var $hasOne = array('Result', 'Point', 'Writeup', 'Timetable', 'Photo');
Now am doing a query and only want to pull out Sport, Point, and Timetable
Which would result in me retrieving Sports, Events, Points, and Timetable.
Reason for not pulling everything is due the results having 17000+ rows.
Is there a way to only select those tables using:
$this->Event->find('all');
I have had a look at the API but can't see how its done.
You should set recursive to -1 in your app_model and only pull the things you require. never use recursive of 2 and http://book.cakephp.org/view/1323/Containable is awesome.
just $this->Event->find('all', array('contain' => array()));
if you do the trick of recursive as -1 in app_model, this is not needed, if would just be find('all') like you have