I have a Rails application that holds user data (in an aptly named user_data object). I want to display a summary table that shows me the count of total users and the count of users who are still active (status = 'Active'), created each month for the past 12 months.
In SQL against my Postgres database, I can get the result I want with the following query (the date I use in there is calculated by the application, so you can ignore that aspect):
SELECT total.creation_month,
total.user_count AS total_count,
active.user_count AS active_count
FROM
(SELECT date_trunc('month',"creationDate") AS creation_month,
COUNT("userId") AS user_count
FROM user_data
WHERE "creationDate" >= to_date('2015 12 21', 'YYYY MM DD')
GROUP BY creation_month) AS total
LEFT JOIN
(SELECT date_trunc('month',"creationDate") AS creation_month,
COUNT("userId") AS user_count
FROM user_data
WHERE "creationDate" >= to_date('2015 12 21', 'YYYY MM DD')
AND status = 'Active'
GROUP BY creation_month) AS active
ON total.creation_month = active.creation_month
ORDER BY creation_month ASC
How do I write this query with ActiveRecord?
I previously had just the total user count grouped by month in my display, but I am struggling with how to add in the additional column of active user counts.
My application is on Ruby 2.1.4 and Rails 4.1.6.
I gave up on trying to do this the ActiveRecord way. Instead I just constructed my query into a string and passed the string into
ActiveRecord::Base.connection.execute(sql_string)
This had the side effect that my result set came out as a array instead of a set of objects. So getting at the values went from a syntax (where user_data is the name assigned to a single record from the result set) like
user_data.total_count
to
user_data['total_count']
But that's a minor issue. Not worth the hassle.
Related
I have a single logs table which contains entries for users. I want to (prune) delete all but the last 100 for each user. I'd like to do this in the most efficient way (one statement using ActiveRecord if possible).
I know I can use the following:
.order(created_at: :desc) to get the records sorted
.offset(100) to get all records except the ones I want to keep
.ids to pluck the record ids
select(:user_id).distinct to get a list of all users in the table
The table has id, user_id, created_at columns (and others not pertinent to this question).
Each user should have at least the last 100 log entries remaining the logs table.
Not really sure how to do this using ruby syntax with my Log model. If it can't be done efficiently using ruby then I'll resort to using the SQL equivalent.
Any help much appreciated.
In SQL, you could do this:
DELETE FROM logs
USING (SELECT id
FROM (SELECT id,
row_number()
OVER (PARTITION BY user_id
ORDER BY created_at DESC)
AS rownr
FROM logs
) AS a
WHERE rownr > 100
) AS b
WHERE logs.id = b.id;
If the table is large, this will be slow.
I have written a Rails 4 app that accepts and plots sensor data. Sometimes there are 10 points per hour (but this number is not fixed). I'm plotting the data and doing a simple query of Points.all to get all the data points.
In order to reduce the query size, I would like to only return one record per hour. It doesn't matter which record is returned. The first record each hour using the created_at field would be fine.
How do I construct a query to do this?
You can get first one, but maybe average value is better. All you need to do is to group it by hour. I am not 100% about sqlite syntax but something in this sense:
connection.execute("SELECT AVG(READING_VALUE) FROM POINTS GROUP BY STRFTIME('%Y%m%d%H0', CREATED_AT)")
Inspired from this answer, here is an alternative which retrieves the latest record in that hour (if you don't want to average):
Point.from(
Point.select("max(unix_timestamp(created_at)) as max_timestamp")
.group("HOUR(created_at)") # subquery
)
.joins("INNER JOIN points ON subquery.max_timestamp = unix_timestamp(created_at)")
This will result in the following query:
SELECT `points`.*
FROM (
SELECT max(unix_timestamp(created_at)) as max_timestamp
FROM `points`
GROUP BY HOUR(created_at)
) subquery
INNER JOIN points ON subquery.max_timestamp = unix_timestamp(created_at)
You can also use MIN instead to get the first record of the hour, if you like, as well.
I am trying to generate a report to screen of accounting transaction history. In most situations it is one display row per record in the AccountingTransaction table. But occasionally there are transactions that I wish to display to the end user as one transaction which are really, behind the scenes, two accounting transactions. This is caused by deferral of revenues and fund splitting since this app is a fund accounting app.
If I display all rows one by one, those double entries look odd to the user since the fund splitting and deferral is "behind the scenes". So I want to roll up all the related transactions into one display row on screen.
I have my query now using group by to group the related transactions
#history = AccountingTransaction.where("customer_id in (?) AND no_download <> 1", customers_in_account).group(:transaction_type_id, :reference_id).order(:created_at)
as I loop through I get the transactions grouped as I want but I am struggling with how to display the total sum of the 'credit' field for all records in the group. (It is only showing the credit for the first record of the group) If I add a .sum(:credit) to my query, of course, it returns the sums just as I want but not all the other data.
Is there a way for me to group these records like in my #history query and also get the sum of the credit field for each respective group?
* Addition *
What I really want is what the following SQL query would give me.
SELECT transaction_type_id, reference_id, sum(credit)
WHERE customer_id in (21,22,23,24) AND no_download <> 1
GROUP BY reference_id, transaction_type_id ORDER BY created_at
I'm not sure you can do "ORDER BY created_at" and not include it in the select fields, but here is an example.
#history = AccountingTransaction.
select([:reference_id, :transaction_type_id, :created_at]).
select(AccountingTransaction.arel_table[:credit].sum.as("credit_sum")).
where("customer_id in (?) AND no_download <> 1", customers_in_account).
group(:transaction_type_id, :reference_id).
order(:created_at)
To access the credit_sum you could do:
#history[0].attributes["credit_sum"]
I guess if you'd like, you could create a method:
def credit_sum
attributes["credit_sum"]
end
EDIT *
As stated in comments you can access the attribute directly:
#history[0].credit_sum
I'm trying to figure out how to do a query where created_at.year == a given year, and created_at.month equals a given month.
However I can't figure out what I'm doing wrong.
Model.where("'created_at.month' = ? AND 'created_at.year' = ?", 7,2013)
results in nothing being shown.
However when I try Model.first.created_at.month ==7 and
Model.first.created_at.year ==2013 I get true for both.
Therefore theoretically my query should be at least be returning my first record.
Anyone know what I'm doing wrong or any alternative way to find records created on specific months?
Note that in my views the month / year will be parameters but for the purposes of this example I used actual values.
using ruby 1.9.3
rails 3.2.13
You can use the extract SQL function, that will extract the month and year of the timestamp:
Model.where('extract(year from created_at) = ? and extract(month from created_at) = ?', '2013','7')
This query should give you the desired result.
created_at is a timestamp; it is not a set of discrete fields in the database. created_at.year and such don't exist in your DB; it's simply a single timestamp field. When you call #model.created_at.year, Rails is loading the created_at field from the database, and creating a Time object from it, which has a #year method you can call.
What you want is to query on a range of dates:
Model.where("created_at >= ? and created_at < ?", Time.mktime(2013, 7), Time.mktime(2013, 8))
This will find any Model with a created_at timestamp in July 2013.
In one of my models I have a country column. How would I go about selecting the top 3 countries based on how many models have that country?
Without any further information you can try this out:
YourModel.group('country').order('count_country DESC').limit(3).count('country')
when you call count on a field rails automatically adds an AS count_field_name field to your query.
Count must be called at the end of the query because it returns an ordered hash.