I have 2 tables (relationships many-to-many with sqlite3) :
-User
-Credit(with user_id & score)
And I try to compute the rank of the user.
To compute the rank of this user I need to find the SUM of all the credits of this user.
But I don't know how do this :(
I have tried something like this but it don't work :
User.all.join(:credits).order(sum(:score)).index(#user)
I get this error :
TypeError in UsersController#index
can't convert Symbol into String
Thank !
To sum (or count) you should use sum with group (that is converted in "group by"),
because you need to group the users in some way to be able to sum their score.
I did not try the following code, but it should be something like this:
User.select("users.name, sum(credits.score)").joins(:credits).group("credits.user_id")
I hope this helps you
Related
First question ever on here, and pretty new to coding full apps/Rails.
I was creating a method to get the counts for titles by author, and noticed that if the author is cased differently, it would count as different authors. I wanted to place some sort of validation/check to disregard the casing and count it together. I don't care about the casing of the book titles in this particular case.
So I have table like this:
Author Book Title Year Condition
William Shakespeare Hamlet 1599 Poor
Stephen King The Shining 1977 New
Edgar Allen Poe The Raven 1845 Good
JK Rowling Harry Potter and the Sorcerer's Stone 2001 New
edgar allen poe The Tell-Tale Heart 1843 Good
JK Rowling Fantastic Beasts and Where to Find Them 2001 New
I want to output this:
Author Count
William Shakespeare 1
Stephen King 1
Edgar Allen Poe 2
JK Rowling 2
My method was originally something like this:
def self.book_counts
distinct_counts = []
Book.group(:author).count.each do |count|
distinct_counts << count
end
distinct_counts
end
To ignore casing, I referenced this page and came up with these, which didn't end up working out, unfortunately:
1) With this one I get "undefined method lower":
Book.group(lower('author')).count.each do |count|
distinct_counts << count
2) This runs, but with the select method in general, I get a bunch of ActiveRecord results/Record id: nil. I am using Rails 6 and it additionally notes "DEPRECATION WARNING: Dangerous query method (method whose arguments are used as raw SQL) called with non-attribute argument(s) ... Non-attribute arguments will be disallowed in Rails 6.1. This method should not be called with user-provided values, such as request parameters or model attributes. Known-safe values can be passed by wrapping them in Arel.sql(). (called from irb_binding at (irb):579)":
Book.select("lower(author) as dc_auth, count(*) as book_count").group("dc_auth").order("book_count desc")
3) I even tried to test a different, simplified function to see if it'd work, but I got "ActiveRecord::StatementInvalid (PG::GroupingError: ERROR: column "books.author" must appear in the GROUP BY clause or be used in an aggregate function)":
Book.pluck('lower(author) as dc_auth, count(*) as book_count')
4) I've tried various other ways, with additional different errors, e.g. "undefined local variable or method 'dc_auth'", "undefined method 'group' did you mean group_by?", and "wrong number of arguments (given 1, expected 0)" (with group_by), etc.
This query works exactly how I want it to in postgresql. The syntax actually populates in the terminal when I run #2, but as mentioned, unfortunately due to ActiveRecord doesn't output properly in Rails.
SELECT lower(author) as dc_auth, count(*) as book_count FROM books GROUP BY dc_auth;
Is there even a way to run what I want through Rails??
Maybe you can try
Book.group("LOWER(author)").count
You can execute your query using ActiveRecord. And I will suggest to go with SQL block
book_count_query = <<-SQL
SELECT lower(author) as dc_auth, count(*) as book_count
FROM books
GROUP BY dc_auth;
SQL
1- result = ActiveRecord::Base.connection.execute(book_count_query)
or
2- result = ActiveRecord::Base.connection.exec_query(book_count_query)
What difference between line 1 and line 2?
exec_query it returns an ActiveRecords::Result object which has handy methods like .columns and .rows to access headers and values.
The array of hashes from .execute can be troublesome to deal with and gave me redundant results when I ran with a SUM GROUP BY clause.
If you need read more about this topic
example of exec_query in api.rubyonrails
active_record_querying in Rails Documentation
This Resource have example for query and output .
Why you store authors in the same table with books. The better solution is to add a separate table for authors and add a foreign key to author_id to books table. With counter_cache you can easily count the number of books for each author.
Here is a guide with books and authors examples https://guides.rubyonrails.org/association_basics.html
I have several records with several attributes (A, B, C, D).
I want to be able to find which record has the higher value for a given attribute, such as D.
Team.of_city(seller_lead.city).with_access_to(seller_lead.state).max_by{ |team| team.rank }
For example, The above code gives me only one city but there are multiple cities with the same maximum rank. How do I get them all?
I would solve this with a subquery in the database:
Team.where(rank: Team.maximum(:rank)).
of_city(seller_lead.city).
with_access_to(seller_lead.state)
I have a model with following columns
Charges Model
Date
fee
discount
Data
1/1/15, 1, 1
1/1/15, 2, 1
2/2/15, 3, 3
I have a few named scopes like this_year
I want to do something like Charges.this_year.summed_up
How do I make a named scope for this.
The returned response then should be:
1/1/15, 3, 2
2/2/15, 3, 3
Assuming you have a model with a date field(eg. published_at) and 2 integer fields(eg. fee, discount). You can use "group" method to run GROUP BY on published_at. Then just use sum method if you want only sum of one fields. If you want more than one field, you have to run a select with SQL SUMs inside, to get multiple column sums. Here is an example.
Charge..group(published_at)
.select("published_at, SUM(fee) AS sum_fee, SUM(discount) AS sum_discount")
.order("published_at")
Note: Summarized fields won't show up in rails console return value prompt. But they are there for you to use.
Depending upon what end result you want, you may want to look at .group(:attribute) rather than .group_by:
Charge.group(:date).each do |charge|
charge.where('date = ?', charge.date).sum(:fee)
charge.where('date = ?', charge.date).sum(:discount)
end
I found this approach easier, especially if setting multiple conditions on the data you want to extract from the table.
In any case, I had an accounting model that presented this kind of issue where I needed credit and debit plus type of payment info on a single table and spent a fruitful few hours learning all about group_by before realizing that .group() offered a simple solution.
I'm having some problems with my Ruby on Rails website. Let me explain.
I have a user model, it has many credits
In order to count, the credits for a user I do:
#user.credits.sum(:score)
This works fine.
Now have a model team, that has many users, and I want to find out the total number of credits, I found on another StackOverflow post this:
array.inject{|sum,x| sum + x }
So I thought for me it should look like that:
#team.users.inject{|sum,x| sum + x.credits.sum(:score)}
But this returns
#<User:0x00000101a7c180>
instead of the sum. Guess I'm doing something wrong. Don't hesitate if you have an idea.
Thanks
You have to set the initial value:
#team.users.inject(0){ |sum,x| sum + x.credits.sum(:score) }
You could also do:
#team.users.sum{ |x| x.credits.sum(:score) }
Does it possible to have an order by "property" with a where clause and now the "index/position" of the result?
I mean, when using order for sorting we need to be able to know the position of the result in the sort.
Imagine a scoreboard with 1 million user node, i do an order by on user node.score with a where "name = user_name" and i wan't to know the current rank of the user. I do not find how to do this using order by ...
start game=node(1)
match game-[:has_child_user]->user
with user
order by user.score
with user
where user.name = "my_user"
return user , "the position in the sort";
the expected result would be :
node_user | rank
(i don't want to fetch one million entries at client side to know the current rank/position of a node in the ORDER BY!)
This functionality does not exist today in Cypher. Do you have an example of what this would look like in SQL? Would the below be something that fits the bill? (just a sketch, not working!)
(your code)
start game=node(1)
match game-[:has_child_user]->user
with user
order by user.score
(+ this code)
with user, index() as rank
return user.name, rank;
If you have more thoughts or want to start hacking on this please open an issue at https://github.com/neo4j/neo4j/issues
For the time being there is a work around that you can do:
start n=node(0),rank_node=node(1)
match n-[r:rank]->rn
where rn.score <= rank_node.score
return rank_node,count(*) as pos;
For live example see: http://console.neo4j.org/?id=bela20