Just wanted an opinion on this in terms of design and efficiency.
Let's say you have a social network for liking music.
If you have query like music.users and out of those users you want to identify your friends. Visually you want to add a feature to identify these friends, maybe all your friends have a star on their profile and non friends are left alone.
Is it really inefficient/expensive to be checking each user to see if they are a friend? Alternate methods?
result = music.users(:user)
.optional(:friends, :friend)
.where(neo_id: current_user.neo_id)
.pluck(:user, is_friend: 'friend IS NOT NULL')
This would return an array of tuples: Each user from the association, and a boolean stating if they are friends of the current user
The .optional(:friends, :friend) is like calling .friends(:friend), but is uses an OPTIONAL MATCH instead of a MATCH in cypher for querying the association.
For the is_friend part, that translates to RETURN friend IS NOT NULL AS is_friend. Actually, since this is a pluck, the AS isn't necessary, so it could just be .pluck(:user, 'friend IS NOT NULL'). Since it's doing an OPTIONAL MATCH, the friend variable in the query (which is the current_user) will only be there if the user from the result row is friends with the current_user.
One thing that you can do to help with understanding of what the query chain would do is to call to_cypher to see what query would be generated. In this case, that would be:
puts music.users(:user)
.optional(:friends, :friend)
.where(neo_id: current_user.neo_id)
.return(:user, is_friend: 'friend IS NOT NULL')
.to_cypher
The pluck is a method that returns an array instead of a query chain object, so I replaced it with return in this case.
Related
I have a model called lists, which has a column called item_ids. item_ids is a JSON column (MySQL) and the column contains array of UUIDs, each referring to one item.
Now when someone creates a new list, I need to search whether there is an existing list with same set of UUIDs, and I want to do this search using query itself for faster response. Also use ActiveRecord querying as much as possible.
How do i achieve this?
item_ids = ["11E85378-CFE8-39F8-89DC-7086913CFD4B", "11E85354-304C-0664-9E81-0A281BE2CA42"]
v = List.new(item_ids: item_ids)
v.save!
Now, how do I check whether a list exists which has item ids exactly matches with that mentioned in query ? Following wont work.
list_count = List.where(item_ids: item_ids).count
Edit 1
List.where("JSON_CONTAINS(item_ids, ?) ", item_ids.to_json).count
This statement works, but it counts even if only one of the item matches. Looking for exact number of items.
Edit 2
List.where("JSON_CONTAINS( item_ids, ?) and JSON_LENGTH(item_ids) = ?", item_ids.to_json, item_ids.size).count
Looks like this is working
You can implement a has many relation between lists and items and then access like this.
List.includes(:item).where('items.id in (?)',item_ids)
To implement has_many relation:
http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association
So I have this website where people can report some tracks. People can do so even tho they're not member of said website and if they're not members, the system will assign them a random "pseudo member number" (pmn from here on) in the style of "not_a_member_XXXX".
$query_claimed = "SELECT * FROM claims_archive WHERE t20pctID=:t20pctID AND member_name=:member_name AND member_email=:member_email AND (member_number=:member_number OR member_number LIKE '%not_a_member_%')";
$stmt = $con->prepare($query_claimed);
$stmt->bindParam(':t20pctID', $t20pctID);
$stmt->bindParam(':member_name', $member_name);
$stmt->bindParam(':member_number', $member_number);
$stmt->bindParam(':member_email', $member_email);
$stmt->execute();
In the testing period we have had some songs have been reported by the same person with a pseudo-number and some with a member number. My problem is that if I make a query with a pmn and the song exists with the same member name and e-mail but with another member number, the code will insert it instead of displaying a message in the style of "You have already claimed this song".
But if I do the query with the member number, then it will display the above message even if the record has it reported with a pmn.
I thought there was something wrong with my logic, but running the above query on phpMyAdmin, it does show the record if there is any matches. I have read about precedence, in case it applies here, and in case there's some operator order I should know about. What am I doing wrong?
Thanks in advance and I hope I made myself understood (English isn't my first or second language).
EDIT to add some info: although I haven't been able to identify a specific pattern for this issue, I have identified that it happens with this particular record.
Here is my story:
I'm writting a script that permits to see every users in an array of group (I mean, you select 2 group, it show every users in one of these two groups). It also do some other treatment. But it's OK for this part.
Everything seems to work correcly. Except for only one user.
The idea is, I have to get the e-mail of a user, to then compare users'e-mail got in a former group, to see if this user is (or not) already listed ( in order to avoid duplicate).
The user (this one only) won't use my function. I supposed it was a group, but it really is a user.. I'm pretty sure it is an option to select ( or not) in the user's preference, but which one?
PS: here is the error quote
TypeError: Fonction getEmail introuvable dans l'objet
(TypeError: getEmail function not found in object)
And here is the code I use in order to get e-mails:
for(var i in objuser){
for(var j in objuser[i])
{
objuser[i][j]=objuser[i][j].getEmail();
}
}
Objuser is a list of User Object. First dimension (I) is the group, second dimension (j), is users of the "I" group.
PROBLEM NOT SOLVED:
the reason:
I have 2 functions that do treatments. Theses Two function need an array, that another function create (which is long to execute). My code is done in such a way, if i execute consecutively these 2 treatment functions with the same array, the second to be played use an incorrect array.
So i clone it with :
var groupsUser2 = JSON.parse(JSON.stringify(groupsUser));
but, now that i dont use anymore email adresses ( i mean String), but direct Users (i mean Object), the former code don't clone correctly:
array1 : user's array (Objects)
array2 = JSON.parse(JSON.stringify(array1))
log(array1) :[blabla1#...com,blabla2#...com,blabla3#...com, .....]
log(array2) :[{},{},{}………]
SO.... Here is the new question: Is there a simple way to copy an Object's array ?
Here is the former question: What rights configuration unallow me to use the getEmail() function for a specific contact?
I need an answer just for one of these two questions, and i'll be able to correct my problem. Any idea guys???????
never use "for x in array" its bad use of javascript on an array because the array has the "length" property which is a number and not the object your loop expects.
instead use " for (i=0;...." or forEach.
Well, I was using getEmail() function in order to compare users got in one group, to others got in another group , so that i can avoid duplicates.
I was checking with IndexOf() if the user adress were in the array of the other group's users.
I don't know why , but now it works even if i don't get the e-mail of the user. So , the problem that was happening for one user can't happen anymore.
Conclusion: Problem solved. Thx mates
I thought about a solution: try .. catch, so that the email which won't be get, will be potentially duplicated because I will not be able to find the user if already displayed or not without his e-mail, but at least the script will not crash.
I have a design problem with SQL request:
I need to return data looking like:
listChannels:
-idChannel
name
listItems:
-data
-data
-idChannel
name
listItems:
-data
-data
The solution I have now is to send a first request:
*"SELECT * FROM Channel WHERE idUser = ..."*
and then in the loop fetching the result, I send for each raw another request to feel the nested list:
"SELECT data FROM Item WHERE idChannel = ..."
It's going to kill the app and obviously not the way to go.
I know how to use the join keyword, but it's not exactly what I want as it would return a row for each data of each listChannels with all the information of the channels.
How to solve this common problem in a clean and efficient way ?
The "SQL" way of doing this produces of table with columns idchannel, channelname, and the columns for item.
select c.idchannel, c.channelname, i.data
from channel c join
item i
on c.idchannel = i.idchannel
order by c.idchannel, i.item;
Remember that a SQL query returns a result set in the form of a table. That means that all the rows have the same columns. If you want a list of columns, then you can do an aggregation and put the items in a list:
select c.idchannel, c.channelname, group_concat(i.data) as items
from channel c join
item i
on c.idchannel = i.idchannel
group by c.idchannel, c.channelname;
The above uses MySQL syntax, but most databases support similar functionality.
SQL is made for accessing two-dimensional data tables. (There are more possibilities, but they are very complex and maybe not standardized)
So the best way to solve your problem is to use multiple requests. Please also consider using transactions, if possible.
TL;DR? See Edit 2
I've got a little Rails application that has a few different sort of games people can play: it's based around sports, so they can pick the winners of each game every week (model PickEm, attribute correct boolean with nil for unfinished games), and predict the outcome of a specific team's game (model Guess, attribute score with integer, nil for unfinished games). Every User has_many PickEms and Guesses. And I'm trying to display standings (correct/total - total being all non-nil, score/total possible).
What I'm finding is that I can gather the users and their associated records, but in trying to display standings I'm discovering that every single User is triggering another query - slow and not sustainable as the user base increases. That's because #user.pick_em_score is pick_ems.where(correct: true).size and #user.guess_Score is guesses.where.not(score: nil).sum(:score). So I call user.pick_em_score and it runs that query. I feel like there should be a way to get every User, as well as these specific counts, at once, rather than buffering a whole bunch of needless extra stuff.
What I need:
User record
User.pick_em_score (calculated by counting correct records)
User.pick_ems count where NOT NULL
User.guesses_score (calculated by guesses.sum(:score))
User.guesses count where NOT NULL
Most of the stuff I find on Rails's ActiveRecord helpers, especially related to calculations, is for retrieving only the calculation. It looks like I'll probably need to delve directly into select() etc. But I can't get it working. Can someone point me in the right direction?
Edit
For clarification: I'm aware that I can write this information to the User model, but this is overly restrictive: next season, I'll need to add a new column to the User for that year's results, etc. In addition, this is a third degree of callback updating related models – the Match model already updates related PickEms and Guesses on save. I'm looking for the simplest ActiveRecord query or queries to be able to work with this information, as indicated by the title. Ideally one query that returns the above information, but if it needs to a few, that's OK.
I used to work directly in MySQL with PHP, but those skills have rusted (in raw MySQL, I imagine, I'd have several sub-select statements to help pull these counts) and I'd also like to be able to use Rails's ActiveRecord helpers and such, and avoid constructing raw SQL as much as possible.
Second Edit:
I seem to have it down to one call that starts to work, but I'm writing a lot of SQL. It's also brittle, IMO, and trying to run with it has failed. It also looks like I'm just pushing the million singular SELECT queries from Rails right into SQL, but that may still be a step up.
User.unscoped.select('users.*',
'(SELECT COUNT(*) FROM pick_ems WHERE pick_ems.user_id = users.id AND pick_ems.correct) AS correct_pick_ems',
'(SELECT COUNT(*) FROM pick_ems WHERE pick_ems.user_id = users.id AND pick_ems.correct IS NOT NULL) AS total_pick_ems',
'(SELECT SUM(guesses.score) FROM guesses WHERE guesses.user_id = users.id AND guesses.score IS NOT NULL) AS guesses_score',
'(SELECT COUNT(*) FROM guesses WHERE guesses.user_id = users.id AND guesses.score IS NOT NULL) AS guesses_count' )
The issue seems to be: is there a way to use Rails, and not raw SQL, to link up users.id that we see there with these subqueries? Or just … a better way to construct this, in general?
In addition, I'm running another set of SELECTs for the WHERE, which would hinge on total_pick_ems and guesses_count being > 0 but since I can't use those aliased columns, I have to call the SELECT one more time.
Welcome to AR. Its really only good for simple CRUD like queries. Once you actually want to query your data in anger it just doesn't have the capababilities to do the queries you want without resorting to wholesale SQL strings and often abandoning the ability to chain as a result.
Its precisely why I moved to Sequel as it does have the features to compose queries using a much fuller SQL feature set, including join conditions, window functions, recursive common table expressions, and advanced eager loading. The author is incredibly responsive and documentation is excellent compared to AR and Arel.
I don't expect you will like this answer but a time will come when you will start to look outside the opinionated components that come with rails which I have to say are hardly best of breed. Sequel also sped my application up many times over what I was able to get with AR as well, it not just developer happiness, it means less servers to run. Yes it will be a learning curve but IMO its better to learn tools that have your back covered.
Joins might work. Smthing like below
User.unscoped.joins(:guesses).joins(:pick_ems).
where("guesses.score IS NOT NULL").
select("users.*,
sum(guesses.score) as guesses_score,
count(guesses.id) as guesses_count,
count(case when pick_ems.correct = True then 1 else null end)
as correct_pick_ems,
count(case when pick_ems.correct != null then 1 else null end)
as total_pick_ems,
").
group("users.id")
If you need this information for a limited number of users at a time then above query or eager loading (User.includes(:guesses, :pick_ems)) with class methods like
def correct_pick_ems
pick_ems.count(&:correct)
end
would work.
However If you need this information for all the users most of the time, cached counters within the users table would be more optimal.
What you need is some sort of custom (smart) counter_cache to count only at certain conditions (e.g correct is true)
You can achive this using conditional after_save & after_destroy triggers to build your own custom counter_cache that looks like this:
class PickEm
belongs_to :user
after_save :increment_finished_counter_cache, if: Proc.new { |pick_em| pick_em.correct }
after_destroy :decrement_finished_counter_cache, if: Proc.new { |pick_em| pick_em.correct }
private
def increment_finished_counter_cache
self.user.update_column(:finished_games_counter, self.user.finished_games_counter + 1) #update_column should not trigger any validations or callbacks
end
def decrement_finished_counter_cache
self.user.update_column(:finished_games_counter, self.user.finished_games_counter - 1) #update_column should not trigger any validations or callbacks
end
end
Notes:
Code not tested (only to show the idea)
Some guys said it's better to avoid naming custom counters as rails name them (foo_counter_cache)
You should benchmark it, but my hunch is that adding all of that data into a single SELECT isn't going to be much faster than breaking it up into separate SELECTs (I've actually had cases where the latter was faster). By breaking it up, you can also stick to more ActiveRecord and less raw SQL, e.g.:
user_ids_to_pick_em_score = User.joins(:pick_ems).where(pick_ems: {correct: true}).group(:user_id).count
user_ids_to_pick_ems_count = User.joins(:pick_ems).where.not(pick_ems: {correct: nil}).group(:user_id).count
user_ids_to_guesses_score = Hash[User.select("users.id, SUM(guesses.score) AS total_score").joins(:guesses).group(:user_id).map{|u| [u.id, u.total_score]}]
user_ids_to_guesses_count = User.joins(:guesses).where.not(guesses: {score: nil}).group(:user_id).count
Edit: To display them, you could do like so:
<%- User.select(:id, :name).find_each do |u| -%>
Name: <%= u.name %>
Picks Correct: <%= user_ids_to_pick_em_score[u.id] %>/<%= user_ids_to_pick_ems_count[u.id] %>
Total Score: <%= user_ids_to_guesses_score[u.id] %>/<%= user_ids_to_guesses_count[u.id] %>
<%- end -%>