In our rails 3.2 app, we need to retrieve all customer records out of customer table and assign them to a variable customers and do query (such as .where(:active => true) on variable customers late on. There are 2 questions here:
what's the better way to retrieve all records?
Customer.all works. However according to rails document, it may have performance issue when Customer table gets large. We tried Customer.find_each and it has error "no block given (yield)".
How to make the variable customers query_able?
When performing query on variable customers (like customers.where(:active => true)), there is an error: undefined methodwhere' for #. It seems that thecustomersis an array object and can't takewhere. How can we retrievecustomers` in such a way it can be query-able?
Thanks for help.
In Rails < 4 .all makes database call immediately, loads records and returns array. Instead use "lazy" scoped method which returns chainable ActiveRecord::Relation object. E.g.:
customers = Customer.scoped
...
customers = customers.where(:active => true)
customers = customers.where(...)
etc...
And at the moment when you will need to load records and iterate over them you can call find_each:
customers.find_each do |customer|
...
end
Related
I'm not sure if this is just a lacking of the Rails language, or if I am searching all the wrong things here on Stack Overflow, but I cannot find out how to add an attribute to each record in an array.
Here is an example of what I'm trying to do:
#news_stories.each do |individual_news_story|
#user_for_record = User.where(:id => individual_news_story[:user_id]).pluck('name', 'profile_image_url');
individual_news_story.attributes(:author_name) = #user_for_record[0][0]
individual_news_story.attributes(:author_avatar) = #user_for_record[0][1]
end
Any ideas?
If the NewsStory model (or whatever its name is) has a belongs_to relationship to User, then you don't have to do any of this. You can access the attributes of the associated User directly:
#news_stories.each do |news_story|
news_story.user.name # gives you the name of the associated user
news_story.user.profile_image_url # same for the avatar
end
To avoid an N+1 query, you can preload the associated user record for every news story at once by using includes in the NewsStory query:
NewsStory.includes(:user)... # rest of the query
If you do this, you won't need the #user_for_record query — Rails will do the heavy lifting for you, and you could even see a performance improvement, thanks to not issuing a separate pluck query for every single news story in the collection.
If you need to have those extra attributes there regardless:
You can select them as extra attributes in your NewsStory query:
NewsStory.
includes(:user).
joins(:user).
select([
NewsStory.arel_table[Arel.star],
User.arel_table[:name].as("author_name"),
User.arel_table[:profile_image_url].as("author_avatar"),
]).
where(...) # rest of the query
It looks like you're trying to cache the name and avatar of the user on the NewsStory model, in which case, what you want is this:
#news_stories.each do |individual_news_story|
user_for_record = User.find(individual_news_story.user_id)
individual_news_story.author_name = user_for_record.name
individual_news_story.author_avatar = user_for_record.profile_image_url
end
A couple of notes.
I've used find instead of where. find returns a single record identified by it's primary key (id); where returns an array of records. There are definitely more efficient ways to do this -- eager-loading, for one -- but since you're just starting out, I think it's more important to learn the basics before you dig into the advanced stuff to make things more performant.
I've gotten rid of the pluck call, because here again, you're just learning and pluck is a performance optimization useful when you're working with large amounts of data, and if that's what you're doing then activerecord has a batch api you should look into.
I've changed #user_for_record to user_for_record. The # denote instance variables in ruby. Instance variables are shared and accessible from any instance method in an instance of a class. In this case, all you need is a local variable.
I’m using Rails 4.2.7. How do I mass update a field of an array of my models without actually saving that information to the database? I tried
my_objcts_arr.update_all(my_object: my_object)
but this results in the error
NoMethodError: undefined method `update_all' for #<Array:0x007f80a81cae50>
I realize I could iteraet over the array and update each object individually, but I figure there's a slicker, one-line way in Ruby taht I'm not aware of.
update_all needs to be called on a class level active record model/relation, ie User or TaxReturn. Here is one somewhat related SO post showing some examples, and here is the api doc for update_all. It will send the UPDATE directly to the db (it is an active record method, after all), so it is not what you want.
You're best off iterating and updating the value yourself with collect or something similar, which is only one line.
foo = [{:a=>"a", :b=>"b"}, {:a=>"A", :b=>"B:}]
// => [{:a=>"a", :b=>"b"}, {:a=>"A", :b=>"B"}]
foo.collect{|x| x[:a]="C"}
// => ["C", "C"]
foo
// => [{:a=>"C", :b=>"b"}, {:a=>"C", :b=>"B"}]
I'm a rails newbie and am building an app. My current problem is trying to find the average time since the last purchase for each customer of an online store using the app, where we have data about their orders and their customers. The problem is that I'm getting an error that says "undefined method `src_created_at' for nil:NilClass." Right now I'm trying to do this only for customers that have purchased once, and leaving aside those that purchased multiple times.
Here's my code:
#customers = Customer.where(:identity_id => #identity.id)
#single_order_customers = #customers.where("orders_count = ?", 1)
days_since_array = []
#single_order_customers.each do |s|
one_order = Order.where(:identity_id => #identity.id, :src_customer_id => s.src_id)
the_date = one_order[0].src_created_at
purchase_date = the_date.to_date
days_between = (Date.today - purchase_date)
days_since_array << days_between
end
days = days_since_array.inject(:+)
#adslp = days / days_since_array.count
Thanks in advance. I can provide what customer and order data looks like if necessary. Any advice would help, even though I know this question is somewhat vague. I've tried some kind if and unless statements validating presence or nil values and they're not working.
Edit:
Here's what's run in the console:
Order Load (123.0ms) SELECT "orders".* FROM "orders" WHERE "orders"."identity_id" = 2 AND "orders"."src_customer_id" = '114863554'
NoMethodError: undefined method `src_created_at' for nil:NilClass
(The above is several orders successfully run and then breaking on the last I've shown.)
Last point: when I try, specifically, to find nil values for this purpose I don't find any.
Order.where(:identity_id => 2, :src_created_at => nil)
Order Load (209.6ms) SELECT "orders".* FROM "orders" WHERE "orders"."identity_id" = 2 AND "orders"."src_created_at" IS NULL
=> []
For your last point where you tried to find nil values, you are getting an empty array [] because your query returned an empty set (no records matched your query). Trying to access any index on an empty array in rails won't throw an IndexOutOfBoundsException, but will instead just return nil, which is where you are getting your nil from. You are expecting one_order[0] to be an order item, but it is instead nil.
The solution to your problem would be to make sure the Order you are searching for already exists in the database. You might want to check how your orders are being created, e.g. if you use Order.create(params[:order]), do you have any validations that are failing, etc. You can check the orders you have through the rails console; just run Order.all. There should be an Order that has an identity_id of 2 and src_created_at of nil for the last query you wrote to return an actual order in the set.
A quick fix for now would be to remove the extra query to set one_order and just get it from the customer:
...
#single_order_customers.each do |s|
one_order = s.orders.first
the_date = one_order.src_created_at
...
The extra query does not seem to be necessary. You have already filtered #customers by identity_id, and src_customer_id will definitely match s.src_id if you get orders by calling s.orders. Relationships should be set up correctly in the models so that a customer has_many orders. You mentioned that you are just starting with rails; I would highly recommend reading a tutorial for rails first to save yourself headaches like these in the future :)
I'm writing an application that allows users to send one another messages about an 'offer'.
I thought I'd save myself some work and use the Mailboxer gem.
I'm following a test driven development approach with RSpec. I'm writing a test that should ensure that only one Conversation is allowed per offer. An offer belongs_to two different users (the user that made the offer, and the user that received the offer).
Here is my failing test:
describe "after a message is sent to the same user twice" do
before do
2.times { sending_user.message_user_regarding_offer! offer, receiving_user, random_string }
end
specify { sending_user.mailbox.conversations.count.should == 1 }
end
So before the test runs a user sending_user sends a message to the receiving_user twice. The message_user_regarding_offer! looks like this:
def message_user_regarding_offer! offer, receiver, body
conversation = offer.conversation
if conversation.nil?
self.send_message(receiver, body, offer.conversation_subject)
else
self.reply_to_conversation(conversation, body)
# I put a binding.pry here to examine in console
end
offer.create_activity key: PublicActivityKeys.message_received, owner: self, recipient: receiver
end
On the first iteration in the test (when the first message is sent) the conversation variable is nil therefore a message is sent and a conversation is created between the two users.
On the second iteration the conversation created in the first iteration is returned and the user replies to that conversation, but a new conversation isn't created.
This all works, but the test fails and I cannot understand why!
When I place a pry binding in the code in the location specified above I can examine what is going on... now riddle me this:
self.mailbox.conversations[0] returns a Conversation instance
self.mailbox.conversations[1] returns nil
self.mailbox.conversations clearly shows a collection containing ONE object.
self.mailbox.conversations.count returns 2?!
What is going on there? the count method is incorrect and my test is failing...
What am I missing? Or is this a bug?!
EDIT
offer.conversation looks like this:
def conversation
Conversation.where({subject: conversation_subject}).last
end
and offer.conversation_subject:
def conversation_subject
"offer-#{self.id}"
end
EDIT 2 - Showing the first and second iteration in pry
Also...
Conversation.all.count returns 1!
and:
Conversation.all == self.mailbox.conversations returns true
and
Conversation.all.count == self.mailbox.conversations.count returns false
How can that be if the arrays are equal? I don't know what's going on here, blown hours on this now. Think it's a bug?!
EDIT 3
From the source of the Mailboxer gem...
def conversations(options = {})
conv = Conversation.participant(#messageable)
if options[:mailbox_type].present?
case options[:mailbox_type]
when 'inbox'
conv = Conversation.inbox(#messageable)
when 'sentbox'
conv = Conversation.sentbox(#messageable)
when 'trash'
conv = Conversation.trash(#messageable)
when 'not_trash'
conv = Conversation.not_trash(#messageable)
end
end
if (options.has_key?(:read) && options[:read]==false) || (options.has_key?(:unread) && options[:unread]==true)
conv = conv.unread(#messageable)
end
conv
end
The reply_to_convesation code is available here -> http://rubydoc.info/gems/mailboxer/frames.
Just can't see what I'm doing wrong! Might rework my tests to get around this. Or ditch the gem and write my own.
see this Rails 3: Difference between Relation.count and Relation.all.count
In short Rails ignores the select columns (if more than one) when you apply count to the query. This is because
SQL's COUNT allows only one or less columns as parameters.
From Mailbox code
scope :participant, lambda {|participant|
select('DISTINCT conversations.*').
where('notifications.type'=> Message.name).
order("conversations.updated_at DESC").
joins(:receipts).merge(Receipt.recipient(participant))
}
self.mailbox.conversations.count ignores the select('DISTINCT conversations.*') and counts the join table with receipts, essentially counting number of receipts with duplicate conversations in it.
On the other hand, self.mailbox.conversations.all.count first gets the records applying the select, which gets unique conversations and then counts it.
self.mailbox.conversations.all == self.mailbox.conversations since both of them query the db with the select.
To solve your problem you can use sending_user.mailbox.conversations.all.count or sending_user.mailbox.conversations.group('conversations.id').length
I have tended to use the size method in my code. As per the ActiveRecord code, size will use a cached count if available and also returns the correct number when models have been created through relations and have not yet been saved.
# File activerecord/lib/active_record/relation.rb, line 228
def size
loaded? ? #records.length : count
end
There is a blog on this here.
In Ruby, #length and #size are synonyms and both do the same thing: they tell you how many elements are in an array or hash. Technically #length is the method and #size is an alias to it.
In ActiveRecord, there are several ways to find out how many records are in an association, and there are some subtle differences in how they work.
post.comments.count - Determine the number of elements with an SQL COUNT query. You can also specify conditions to count only a subset of the associated elements (e.g. :conditions => {:author_name => "josh"}). If you set up a counter cache on the association, #count will return that cached value instead of executing a new query.
post.comments.length - This always loads the contents of the association into memory, then returns the number of elements loaded. Note that this won't force an update if the association had been previously loaded and then new comments were created through another way (e.g. Comment.create(...) instead of post.comments.create(...)).
post.comments.size - This works as a combination of the two previous options. If the collection has already been loaded, it will return its length just like calling #length. If it hasn't been loaded yet, it's like calling #count.
It is also worth mentioning to be careful if you are not creating models through associations, as the related model will not necessarily have those instances in its association proxy/collection.
# do this
mailbox.conversations.build(attrs)
# or this
mailbox.conversations << Conversation.new(attrs)
# or this
mailbox.conversations.create(attrs)
# or this
mailbox.conversations.create!(attrs)
# NOT this
Conversation.new(mailbox_id: some_id, ....)
I don't know if this explains what's going on, but the ActiveRecord count method queries the database for the number of records stored. The length of the Relation could be different, as discussed in http://archive.railsforum.com/viewtopic.php?id=6255, although in that example, the number of records in the database was less than the number of items in the Rails data structure.
Try
self.mailbox.conversations.reload; self.mailbox.conversations.count
or perhaps
self.mailbox.reload; self.mailbox.conversations.count
or, if neither of those work, just try reloading as many of the objects as possible to see if you can get it to work (self, mailbox, conversations, etc.).
My guess is that something is messed up between memory and the DB. This is definitely a really weird error though, might wanna put in an issue on Rails to see why this would be the case.
The result of mailbox.conversations is cached after the first call. To reload it write mailbox.conversations(true)
I don't know if there's a good answer for this. Let's say I have:
users = User.where(:location => "Utopia") #=> Returns [user1,user2,user3,user4]
I would like do something like:
users.photos #=> Returns all photos this group of users has
And simply get all the photos back without iterating over them. I ask because each iteration is a DB call. Is there any good way that does a single DB call?
The most straightforward way to do this is to use the eager loader:
users = User.where(:location => 'Utopia').includes(:photos)
That will fetch the users in one pass, then the relationships and their associated photos in another. You can wrap it all up into one call if you either use a JOIN or a subselect, it's your call, but it'll look something like this:
photos = Photo.includes(:user).where('users.location' => 'Utopia')
There's more information available in the Active Record Query Interface documentation in section 12.