I have this use case where I get the symbolized deep associations from a certain model, and I have to perform certain queries that involve using outer joins. How can one do it WITHOUT resorting to write the full SQL by hand?
Answers I don't want:
- using includes (doesn't solve deep associations very well ( .includes(:cars => [:windows, :engine => [:ignition]..... works unexpectedly ) and I don't want its side-effects)
- writing the SQL myself (sorry, it's 2013, cross-db support, etc etc..., and the objects I fetch are read_only, more side-effects)
I'd like to have an Arel solution. I know that using the arel_table's from the models I can construct SQL expressions, there's also a DSL for the joins, but somehow i cannot use it in the joins method from the model:
car = Car.arel_table
engine = Engine.arel_table
eng_exp = car.join(engine).on(car[:engine_id].eq(engine[:id]))
eng_exp.to_sql #=> GOOD! very nice!
Car.joins(eng_exp) #=> Breaks!!
Why this doesn't work is beyond me. I don't know exactly what is missing. But it's the closest thing to a solution I have now. If somebody could help me completing my example or provide me with a nice work-around or tell me when will Rails include such an obviously necessary feature will have my everlasting gratitude.
This is an old question, but for the benefit of anyone finding it through search engines:
If you want something you can pass into .joins, you can either use .create_join and .create_on:
join_on = car.create_on(car[:engine_id].eq(engine[:id]))
eng_join = car.create_join(engine, join_on, Arel::Nodes::OuterJoin)
Car.joins(eng_join)
OR
use the .join_sources from your constructed join object:
eng_exp = car.join(engine, Arel::Nodes::OuterJoin).on(car[:engine_id].eq(engine[:id]))
Car.joins(eng_exp.join_sources)
I found a blog post that purports to address this problem: http://blog.donwilson.net/2011/11/constructing-a-less-than-simple-query-with-rails-and-arel/
Based on this (and my own testing), the following should work for your situation:
car = Car.arel_table
engine = Engine.arel_table
sql = car.project(car[Arel.star])
.join(engine, Arel::Nodes::OuterJoin).on(car[:engine_id].eq(engine[:id]))
Car.find_by_sql(sql)
If you don't mind adding a dependency and skipping AREL altogether, you could use Ernie Miller's excellent Squeel gem. It would be something like
Car.joins{engine.outer}.where(...)
This would require that the Car model be associated with Engine like so:
belongs_to :engine
Related
I have updated this question
I have the following SQL scope in a RAILS 4 app, it works, but has a couple of issues.
1) Its really RAW SQL and not the rails way
2) The string interpolation opens up risks with SQL injection
here is what I have:
scope :not_complete -> (user_id) { joins("WHERE id NOT IN
(SELECT modyule_id FROM completions WHERE user_id = #{user_id})")}
The relationship is many to many, using a join table called completions for matching id(s) on relationships between users and modyules.
any help with making this Rails(y) and how to set this up to take the arg of user_id with out the risk, so I can call it like:
Modyule.not_complete("1")
Thanks!
You should have added few info about the models and their assocciation, anyways here's my trial, might have some errors because I don't know if the assocciation is one to many or many to many.
scope :not_complete, lambda do |user_id|
joins(:completion).where.not( # or :completions ?
id: Completion.where(user_id: user_id).pluck(modyule_id)
)
end
PS: I turned it into multi line just for readability, you can change it back to a oneline if you like.
I'm wondering if anyone has experience using Ransack with HABTM relationships. My app has photos which have a habtm relationship with terms (terms are like tags). Here's a simplified explanation of what I'm experiencing:
I have two photos: Photo 1 and Photo 2. They have the following terms:
Photo 1: A, B, C
Photo 2: A, B, D
I built a ransack form, and I make checkboxes in the search form for all the terms, like so:
- terms.each do |t|
= check_box_tag 'q[terms_id_in][]', t.id
If I use: q[terms_id_in][] and I check "A, C" my results are Photo 1 and Photo 2. I only want Photo 1, because I asked for A and C, in this query I don't care about B or D but I want both A and C to be present on a given result.
If I use q[terms_id_in_all][] my results are nil, because neither photo includes only A and C. Or, perhaps, because there's only one term per join, so no join matches both A and C. Regardless, I want just Photo 1 to be returned.
If I use any variety of q[terms_id_eq][] I never get any results, so I don't think that works in this case.
So, given a habtm join, how do you search for models that match the given values while ignoring not given values?
Or, for any rails/sql gurus not familiar with Ransack, how else might you go about creating a search form like I'm describing for a model with a habtm join?
Update: per the answer to related question, I've now gotten as far as constructing an Arel query that correctly matches this. Somehow you're supposed to be able to use Arel nodes as ransackers, or as cdesrosiers pointed out, as custom predicates, but thus far I haven't gotten that working.
Per that answer, I setup the following ransack initializer:
Ransack.configure do |config|
config.add_predicate 'has_terms',
:arel_predicate => 'in',
:formatter => proc {|term_ids| Photo.terms_subquery(term_ids)},
:validator => proc {|v| v.present?},
:compounds => true
end
... and then setup the following method on Photo:
def self.terms_subquery(term_ids)
photos = Arel::Table.new(:photos)
terms = Arel::Table.new(:terms)
photos_terms = Arel::Table.new(:photos_terms)
photos[:id].in(
photos.project(photos[:id])
.join(photos_terms).on(photos[:id].eq(photos_terms[:photo_id]))
.join(terms).on(photos_terms[:term_id].eq(terms[:id]))
.where(terms[:id].in(term_ids))
.group(photos.columns)
.having(terms[:id].count.eq(term_ids.length))
).to_sql
end
Unfortunately this doesn't seem to work. While terms_subquery produces the correct SQL, the result of Photo.search(:has_terms => [2,5]).result.to_sql is just "SELECT \"photos\".* FROM \"photos\" "
With a custom ransack predicate defined as in my answer to your related question, this should work with a simple change to your markup:
- terms.each do |t|
= check_box_tag 'q[id_has_terms][]', t.id
UPDATE
The :formatter doesn't do what I thought, and seeing as how the Ransack repo makes not a single mention of "subquery," you may not be able to use it for what you're trying to do, after all. All available options seem to be exhausted, so there would be nothing left to do but monkey patch.
Why not just skip ransack and query the "photos" table as you normally would with active record (or even with the Arel query you now have)? You already know the query works. Is there a specific benefit you hoped to reap from using Ransack?
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.
This is just a quick question on performance in an sql query using ruby and rails.
Basically I have a parent model and a bunch of children which have the variable of parent_ID.
I first gather all the parents with a specific condition and then I cycle through each parent finding any children that match.
Unfortunately this is incredibly slow and I was wondering if theres any help going in optimizing it.
#parents = Parent.where(:parent_id => 3) #This is passed in from params
#childrenArray =[]
#parents.each_with_index do |parent, index|
#TOOSLOW
#childrenArray[index] = Child.find(:all,:order=>"id",:conditions =>{:parent_ID=> parent.id})
end
One thing I thought is perhaps I should make an array of all the parent Ids to be searched and then do something like
child.find_by_parent_ID(myarrayofnumbershere)
However I don't know if this would be any better.
Any help or advice appreciated.
I'm very new to SQL and ruby. I'm aware a table joins would have been ideal here but I think I'm a bit late in my development to try it now. Also I need to serve up 2 seperate arrays. one of the parents and one of the children.
Try using the include method, like so:
#parents = Parent.where(:parent_id => 3).include(:children)
Now rails will have fetched the associated children and you should be able to loop over #parents and access their children without additional queries, like so:
#parents.each do |p|
puts "#{p}'s children: #{p.children}"
end
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