In my models, I have users (User) and stories (Story), with the relation: user has_many stories.
I've noticed something strange in my shell:
(dev) user.stories.any?
=> true
(dev) user.stories
Story Load (1.6ms) SELECT "stories".* FROM "stories" WHERE "stories"."user_id" = 703 ORDER BY created_at ASC [["user_id", 703]]
=> []
(dev) user.stories.any?
=> false
How does this work? Is this due to my code, or is it a bug of some sort in Rails and the way it queries the database?
A workaround I found (thanks to #house9) is to use:
user.stories.to_a.any?
user.stories.to_a.empty? # also works with empty?
This way, Rails is forced to make the query. And the overhead is quite low since doing to_a.any?several times only does the query once.
Or better, as #Jordan suggested, use:
user.stories.exists?
Related
In Rails 3.2.17, i could have the following:
scope :sorted, -> { joins(:other).order({:other => :code}, :code) }
Which produces the following SQL:
SELECT [things].* FROM [things] INNER JOIN [others] ON [others].[id] = [things].[other_id] ORDER BY [others].[code] ASC, [things].[code] ASC
The same code in Rails 4.0.4 gives the following error, however:
Direction should be :asc or :desc
But, I cannot figure out a way to keep the ordering and specify the direct. The scope below, for example, gives the same error:
scope :sorted, -> { joins(:other).order({:other => {:code => :asc}}, :code => :asc) }
EDIT: To be clear, I want to use the Hash style syntax and do not want to write raw SQL strings
This looks like a bug in Rails 4.0+ (something about order accepting nested hashes)
I found a Github issue for you explaining the issue
They recommend using source:, but that's only for an association declaration. If you find the answer, I will gladly remove this, but hopefully it will help you!
I saw the following code example:
Subscription.where(:created_at.gte => t0)`
To me, this seems a little more ruby/rails-like as opposed to:
Subscription.where("created_at > ?", t0)`
However, attempting to reproduce this in my own code on results in:
undefined method `gte' for :created_at:Symbol
I'm not certain, but I believe this is a MongoDB method. If so is there any way I can extend ActiveRecord to make use of it?
You are correct. This is mongoid query DSL.
Similar way to extend ActiveRecord is achieved using squeel gem. However, it is slightly different.
Subscription.where{ created_at.gte => t0 }
Notice different brackets and created_at is not a symbol.
SQL:
select * from user where room_id not in (select id from rooms);
what is the same equivalent query in rails console with this sql?
ex:
User.all.each { |u| user.room }
(sorry, but this example is not correct.)
You can translate it almost literally:
User.where('room_id not in (select id from rooms)').all
The where clause is quite flexible in what it accepts.
User.where("room_id not in (select id from rooms)")
but you want this since it would be rather faster:
User.where("not exist (select id from rooms where id=users.room_id)")
that's the closest you can get. There appears to be no way to create an Active Record query that translates to SQL NOT(). A search on the subject returns a bunch of SO questions with much the same answer.
You could do something like
User.all.select { |u| !Room.find_by_id(u.room_id) }
But that could be less efficient again.
I don't know if you are familiar with the squeel gem. It allows allows you to build very complex SQL-queries in a pure Ruby code. In your case it should be as simple as the following code (afer adding the gem 'squeel' line in your Gemfile and running bundle install):
room_ids = Room.select{id}; User.where{room_id.not_in room_ids}
Worth trying, isn't it?
Here's the squeel's page.
I'm writing a Rails 3 ActiveRecord query using the "where" syntax, that uses both the SQL IN and the SQL OR operator and can't figure out how to use both of them together.
This code works (in my User model):
Question.where(:user_id => self.friends.ids)
#note: self.friends.ids returns an array of integers
but this code
Question.where(:user_id => self.friends.ids OR :target => self.friends.usernames)
returns this error
syntax error, unexpected tCONSTANT, expecting ')'
...user_id => self.friends.ids OR :target => self.friends.usern...
Any idea how to write this in Rails, or just what the raw SQL query should be?
You don't need to use raw SQL, just provide the pattern as a string, and add named parameters:
Question.where('user_id in (:ids) or target in (:usernames)',
:ids => self.friends.ids, :usernames => self.friends.usernames)
Or positional parameters:
Question.where('user_id in (?) or target in (?)',
self.friends.ids, self.friends.usernames)
You can also use the excellent Squeel gem, as #erroric pointed out on his answer (the my { } block is only needed if you need access to self or instance variables):
Question.where { user_id.in(my { self.friends.ids }) |
target.in(my { self.friends.usernames }) }
Though Rails 3 AR doesn't give you an or operator you can still achieve the same result without going all the way down to SQL and use Arel directly. By that I mean that you can do it like this:
t = Question.arel_table
Question.where(t[:user_id].in(self.friends.ids).or(t[:username].in(self.friends.usernames)))
Some might say it ain't so pretty, some might say it's pretty simply because it includes no SQL. Anyhow it most certainly could be prettier and there's a gem for it too: MetaWhere
For more info see this railscast: http://railscasts.com/episodes/215-advanced-queries-in-rails-3
and MetaWhere site: http://metautonomo.us/projects/metawhere/
UPDATE: Later Ryan Bates has made another railscast about metawhere and metasearch: http://railscasts.com/episodes/251-metawhere-metasearch
Later though Metawhere (and search) have become more or less legacy gems. I.e. they don't even work with Rails 3.1. The author felt they (Metawhere and search) needed drastic rewrite. So much that he actually went for a new gem all together. The successor of Metawhere is Squeel. Read more about the authors announcement here:
http://erniemiller.org/2011/08/31/rails-3-1-and-the-future-of-metawhere-and-metasearch/
and check out the project home page:
http://erniemiller.org/projects/squeel/
"Metasearch 2.0" is called Ransack and you can read something about it from here:
http://erniemiller.org/2011/04/01/ransack-the-library-formerly-known-as-metasearch-2-0/
Alternatively, you could use Squeel. To my eyes, it is simpler. You can accomplish both the IN (>>) and OR (|) operations using the following syntax:
Question.where{(:user_id >> my{friends.id}) | (:target >> my{friends.usernames})}
I generally wrap my conditions in (...) to ensure the appropriate order of operation - both the INs happen before the OR.
The my{...} block executes methods from the self context as defined before the Squeel call - in this case Question. Inside of the Squeel block, self refers to a Squeel object and not the Question object (see the Squeel Readme for more). You get around this by using the my{...} wrapper to restore the original context.
raw SQL
SELECT *
FROM table
WHERE user_id in (LIST OF friend.ids) OR target in (LIST OF friends.usernames)
with each list comma separate. I don't know the Rails ActiveRecord stuff that well. For AND you would just put a comma between those two conditions, but idk about OR
In a Rails app, I have a model, Machine, that contains the following named scope:
named_scope :needs_updates, lambda {
{ :select => self.column_names.collect{|c| "\"machines\".\"#{c}\""}.join(','),
:group => self.column_names.collect{|c| "\"machines\".\"#{c}\""}.join(','),
:joins => 'LEFT JOIN "machine_updates" ON "machine_updates"."machine_id" = "machines"."id"',
:having => ['"machines"."manual_updates" = ? AND "machines"."in_use" = ? AND (MAX("machine_updates"."date") IS NULL OR MAX("machine_updates"."date") < ?)', true, true, UPDATE_THRESHOLD.days.ago]
}
}
This named scope works fine in development mode. In production mode, however, it returns the 2 models as expected, but the models are empty or uninitialized; that is, actual objects are returned (not nil), but all the fields are nil. For example, when inspecting the return value of the named scope in the console, the following is returned:
[#<Machine >, #<Machine >]
But, as you can see, all the fields of the objects returned are set to nil.
The production and development environments are essentially the same. Both are using a SQLite database. Here is the SQL statement that is generated for the query:
SELECT
"machines"."id",
"machines"."machine_name",
"machines"."hostname",
"machines"."mac_address",
"machines"."ip_address",
"machines"."hard_drive",
"machines"."ram",
"machines"."machine_type",
"machines"."use",
"machines"."comments",
"machines"."in_use",
"machines"."model",
"machines"."vendor_id",
"machines"."operating_system_id",
"machines"."location",
"machines"."acquisition_date",
"machines"."rpi_tag",
"machines"."processor",
"machines"."processor_speed",
"machines"."manual_updates",
"machines"."serial_number",
"machines"."owner"
FROM
"machines"
LEFT JOIN
"machine_updates" ON "machine_updates"."machine_id" = "machines"."id"
GROUP BY
"machines"."id",
"machines"."machine_name",
"machines"."hostname",
"machines"."mac_address",
"machines"."ip_address",
"machines"."hard_drive",
"machines"."ram",
"machines"."machine_type",
"machines"."use",
"machines"."comments",
"machines"."in_use",
"machines"."model",
"machines"."vendor_id",
"machines"."operating_system_id",
"machines"."location",
"machines"."acquisition_date",
"machines"."rpi_tag",
"machines"."processor",
"machines"."processor_speed",
"machines"."manual_updates",
"machines"."serial_number",
"machines"."owner"
HAVING
"machines"."manual_updates" = 't'
AND "machines"."in_use" = 't'
AND (MAX("machine_updates"."date") IS NULL
OR MAX("machine_updates"."date") < '2010-03-26 13:46:28')
Any ideas what's going wrong?
This might not be related to what is happening to you, but it sounds similar enough, so here it goes: are you using the rails cache for anything?
I got nearly the same results as you when I tried to cache the results of a query (as explained on railscast #115).
I tracked down the issue to a still open rails bug that makes cached ActiveRecords unusable - you have to choose between not using cached AR or applying a patch and getting memory leaks.
The cache works ok with non-AR objects, so I ended up "translating" the stuff I needed to integers and arrays, and cached that.
Hope this helps!
Seems like the grouping may be causing the problem. Is the data also identical in both dev & production?
Um, I'm not sure you're having the problem you think you're having.
[#<Machine >, #<Machine >]
implies that you have called "inspect" on the array... but not on each of the individual machine-objects inside it. This may be a silly question, but have you actually tried calling inspect on the individual Machine objects returned to really see if they have nil in the columns?
Machine.needs_updates.each do |m|
p m.inspect
end
?
If that does in fact result in nil-column data. My next suggestion is that you copy the generated SQL and go into the standard mysql interface and see what you get when you run that SQL... and then paste it into your question above so we can see.