Student has_many :enrollments
With this query I see those students that have true enrollments, but also those that have both, true and false enrollments:
#students = Student.joins(:enrollments).where(enrollments: { is_active: false })
Is there some "only" attribute that I can add to see students that have only active enrollments?
One way straightforward would be to find the students that inactive enrolments and then explicitly exclude them. Something like:
have_inactives = Enrollment.where(is_active: false).select(:student_id)
#students = Student.joins(:enrollments).where.not(id: have_inactives)
The joins(:enrollments) will filter out Student entries that don't have any enrolments and the where.not(...) will exclude all those students that have inactive enrolments (using a subquery so all the work will still be inside the database where it belongs).
BTW, you might want to fix your spelling of "enrolment", the double-l misspelling will probably end up driving you or someone other programmer crazy.
Related
I can disable STI for a complete model but I'd like to just disable it when doing certain queries. Things were working swell in Rails 3.2, but I've upgraded to Rails 4.1.13 and a new thing is happening that's breaking the query.
I have a base class called Person with a fairly complex scope.
class Person < ActiveRecord::Base
include ActiveRecord::Sanitization
has_many :approvals, :dependent => :destroy
has_many :years, through: :approvals
scope :for_current_or_last_year, lambda {
joins(:approvals).merge(Approval.for_current_or_last_year) }
scope :for_current_or_last_year_latest_only, ->{
approvals_sql = for_current_or_last_year.select('person_id AS ap_person_id, MAX(year_id) AS max_year, year_id AS ap_year_id, status_name AS ap_status_name, active AS ap_active, approved AS ap_approved').group(:id).to_sql
approvals_sql = select("*").from("(#{approvals_sql}) AS ap, approvals AS ap2").where('ap2.person_id = ap.ap_person_id AND ap2.year_id = ap.max_year').to_sql
select("people.id, ap_approved, ap_year_id, ap_status_name, ap_active").
joins("JOIN (#{approvals_sql}) filtered_people ON people.id =
filtered_people.person_id").uniq
}
end
And inheriting classes called Member and Staff. The only thing related to this I had to comment out to get my tests to pass with Rails 4. It may be the problem, but uncommenting it hasn't helped in this case.
class Member < Person
#has_many :approvals, :foreign_key => 'person_id', :dependent => :destroy, :class_name => "MemberApproval"
end
The problem happens when I do the query Member.for_current_or_last_year_latest_only
I get the error unknown column 'people.type'
When I look at the SQL, I can see the problem line but I don't know how to remove it or make it work.
Member.for_current_or_last_year_latest_only.to_sql results in.
SELECT DISTINCT people.id, ap_approved, ap_year_id, ap_status_name, ap_active
FROM `people`
JOIN (SELECT * FROM (SELECT person_id AS ap_person_id, MAX(year_id) AS max_year, year_id AS ap_year_id, status_name AS ap_status_name, active AS ap_active, approved AS ap_approved
FROM `people` INNER JOIN `approvals` ON `approvals`.`person_id` = `people`.`id`
WHERE `people`.`type` IN ('Member') AND ((`approvals`.`year_id` = 9 OR `approvals`.`year_id` = 8))
GROUP BY `people`.`id`) AS ap, approvals AS ap2
WHERE `people`.`type` IN ('Member') AND (ap2.person_id = ap.ap_person_id AND ap2.year_id = ap.max_year)) filtered_people ON people.id = filtered_people.person_id
WHERE `people`.`type` IN ('Member')
If I remove people.type IN ('Member') AND from the beginning of the second to last WHERE clause the query runs successfully. And btw, that part isn't in the query generated from the old Rails 3.2 code, neither is the one above it (only the last one matches the Rails 3.2 query). The problem is, that part is being generated from rails Single Table Inheritance I assume, so I can't just delete it from my query. It's not the only place that is getting added into the original query, but that's the only one that is causing it to break.
Does anybody have any idea how I can either disable STI for only certain queries or add something to my query that will make it work? I've tried putting people.type in every one of the SELECT queries to try and make it available but to no avail.
Thanks for taking the time to look at this.
I was apparently making this harder than it really was...I just needed to add unscoped to the front of the two approval_sql sub-queries. Thanks for helping my brain change gears.
I have a has_one condition that I'm trying to access but am having a little trouble
Solicitation belongs_to :lead
Lead has_many :solicitations
My first statement grabs all solicitations for a user
#solicitations = current_user.solicitations.includes(:lead)
I can already access the attribute lead.case_type and could just cycle through the relation and put them in their places manually, but I figure their is an easier way.
What I am trying to do is something similar to
#solicitations.where("lead.case_type = ?", "Civil")
I have tried these and receive an unknown column error lead.case_type
Solicitation.all(:conditions => {:lead => {:case_type => 'Civil'}}, :joins => :lead)
The problem is that you are using lead.case_type, but (if you're following Rails' conventions) your table name is leads. This should work:
#solicitations = current_user.solicitations.includes(:lead).where("leads.case_type = ?", "Civil")
You could also use joins for that:
#solicitations = current_user.solicitations.joins(:lead).where("leads.case_type = ?", "Civil")
includes does an outer join, whereas joins does an inner join. Since you're querying the joined table an inner join would be better here.
In where you always have to use the table name (plural), but in includes and joins it depends on the relationship. In this case solicitation belongs to lead, so you have to use :lead (singular). It's a bit confusing, but I hope this clears it up for you.
I'm working on a Rails 3.2 app that uses Datamapper as its ORM. I'm looking for a way to sort a result set by an attribute of the associated model. Specifically I have the following models:
class Vehicle
include DataMapper::Resource
belongs_to :user
end
class User
include DataMapper::Resource
has n, :vehicles
end
Now I want to be able to query the vehicles and sort them by the name of the driver. I tried the following but neither seems to work with Datamapper:
> Vehicle.all( :order => 'users.name' )
ArgumentError: +options[:order]+ entry "users.name" does not map to a property in Vehicle
> Vehicle.all( :order => { :users => 'name' } )
ArgumentError: +options[:order]+ entry [:users, "name"] of an unsupported object Array
Right now I'm using Ruby to sort the result set post-query but obviously that's not helping performance any, also it stops me from further chaining on other scopes.
I spent some more time digging around and finally turned up an old blog which has a solution to this problem. It involves manually building the ordering query in DataMapper.
From: http://rhnh.net/2010/12/01/ordering-by-a-field-in-a-join-model-with-datamapper
def self.ordered_by_vehicle_name direction = :asc
order = DataMapper::Query::Direction.new(vehicle.name, direction)
query = all.query
query.instance_variable_set("#order", [order])
query.instance_variable_set("#links", [relationships['vehicle'].inverse])
all(query)
end
This will let you order by association and still chain on other scopes, e.g.:
User.ordered_by_vehicle_name(:desc).all( :name => 'foo' )
It's a bit hacky but it does what I wanted it to do at least ;)
Note: I'm not familiar with DataMapper and my answer might not be within the standards and recommendations of using DataMapper, but it should hopefully give you the result you're looking for.
I've been looking through various Google searches and the DataMapper documentation and I haven't found a way to "order by assocation attribute". The only solution I have thought of is "raw" SQL.
The query would look like this.
SELECT vehicles.* FROM vehicles
LEFT JOIN users ON vehicles.user_id = users.id
ORDER BY users.name
Unfortunately, from my understanding, when you directly query the database you won't get the Vehicle object, but the data from the database.
From the documentation: http://datamapper.org/docs/find.html. It's near the bottom titled "Talking directly to your data-store"
Note that this will not return Zoo objects, rather the raw data straight from the database
Vehicle.joins(:user).order('users.name').all
or in Rails 2.3,
Vehicle.all(:joins => "inner join users on vehicles.user_id = user.id", :order => 'users.name')
I'm trying to find a record by associated username which is included in a belongs_to relation, but it's not working.
Articles belong to Users
Users have many articles
Article.where(user_id: someid) works fine, but I'd like to use the username as reference which is stored in the Users table.
Article.includes(:user).where(:username => "erebus")
Article.includes(:user).where("user.username" => "erebus")
I also have identity_map_enabled: true
Article.includes(:user).inclusions returns the relation details
Doesn't work, what am I not understanding?
You have to keep in mind that there are no joins in mongodb. In relational dbs, includes forms a join query and you can use columns from both the tables in query. However due to absence of joins in mongodb, same is not possible.
In mongoid, includes just saves a bunch of db calls. It fetches and stores the associated records in identity map for fast retrieval, but still while querying, one query can only deal with one collection.
If you need articles based on user names, I would suggest following work around:
user_ids = User.where(username: 'erebus').only(:_id).map(&:_id)
articles = Article.where(:user_id.in => user_ids)
You can make it little shorter from what rubish suggested:
user_ids = User.where(username: 'erebus').pluck(:id)
articles = Article.where(:user_id.in => user_ids)
Or one liner:
articles = Article.where(:user_id.in => User.where(username: 'erebus').pluck(:id))
I am using Rails 3.0. I have two tables: Listings and Offers. A Listing has-many Offers. An offer can have accepted be true or false.
I want to select every Listing that does not have an Offer with accepted being true. I tried
Listing.joins(:offers).where('offers.accepted' => false)
However, since a Listing can have many Offers, this selects every listing that has non-accepted Offers, even if there is an accepted Offer for that Listing.
In case that isn't clear, what I want is the complement of the set:
Listing.joins(:offers).where('offers.accepted' => true)
My current temporary solution is to grab all of them and then do a filter on the array, like so:
class Listing < ActiveRecord::Base
...
def self.open
Listing.all.find_all {|l| l.open? }
end
def open?
!offers.exists?(:accepted => true)
end
end
I would prefer if the solution ran the filtering on the database side.
The first thing that comes to mind is to do essentially the same thing you're doing now, but in the database.
scope :accepted, lambda {
joins(:offers).where('offers.accepted' => true)
}
scope :open, lambda {
# take your accepted scope, but just use it to get at the "accepted" ids
relation = accepted.select("listings.id")
# then use select values to get at those initial ids
ids = connection.select_values(relation.to_sql)
# exclude the "accepted" records, or return an unchanged scope if there are none
ids.empty? ? scoped : where(arel_table[:id].not_in(ids))
}
I'm sure this could be done more cleanly using an outer join and grouping, but it's not coming to me immediately :-)