There's a way to condition something to an associative table of ActiveRecord?
I retrieve segments this way:
#segments = Segment.all
But, a Segment has_many products. See:
models/product.rb:
class Product < ActiveRecord::Base
belongs_to :segment, dependent: :destroy
end
models/segment.rb:
class Segment < ActiveRecord::Base
has_many :products
end
The problem is: I just want to retrieve products whose its status is equals to 1. I can condition something like this using where on Segment model, but how can I achieve this for products?
What I already tried
I found a solution. Take a look:
#segments = Segment.find(:all, include: :products, conditions: {products: {status: 1}})
It worked, but I think the code can be better.
Why I think the code can be better
Well, why should I use include: :products if the association is already live within the models? We're associating things through the model and I'm sure that is something near to enough.
Ideas?
Segment.joins(:products).where("products.status = 1")
You can also use includes instead of joins. But rails will convert it into a join internally since you are using the products table attribute in the query
A few tips, that might help you.
For easy naming purposes, I am considering the status==1 as being active. Of course I have no idea what it means in your specific case.
class Product
ACTIVE=1
def self.active
where(status: ACTIVE)
end
end
Now you write something like:
segment.products.active
and this will return only the active products for the given segment.
The solution you found, which will retrieve all segments with (active) products, could be written differently as follows:
Segment.includes(:products).where(products: {status: 1})
Now, why so elaborate: this actually translates to a sql query, so you have to be a little more explicit about it.
If you only ever want those with a status of 1
class Segment < ActiveRecord::Base
has_many :products, :conditions => { :status => 1 }
end
In rails 3 or
class Segment < ActiveRecord::Base
has_many :products, -> { where status: 1 }
end
In rails 4
Obviously can use status: true if it's a boolean
Then
#segments = Segment.includes(:products)
The association has_many :products makes it possible to use include: :products in your scope. Therefore you shouldn't doubt in your solution. It is right, and it is just the same as solutions presented in the other answers but by other syntacsis.
This should do the job - and it's compatibile with AREL syntax:
#segments = Segment.joins(:products).where(products: {status: 1})
It's quite different that solution with include (or includes, as it would be Rails 3/4), because it generates query with INNER JOIN, while includes generates LEFT OUTER JOIN. Also, includes is usually used for eager loading associated records, not for queries with JOIN.
Related
Here are the models I created in my Rails app:
class Pet < ActiveRecord::Base
belongs_to :shelter
belongs_to :type
end
class Shelter < ActiveRecord::Base
has_many :pets
end
class Type < ActiveRecord::Base
has_many :pets
end
I'm trying to find shelters that don't have any exotic pets in them but am stuck joining the tables in the way where I can retrieve that information! Here is my latest attempt where I believe I'm at least reaching the Types table. Any help and explanation on joins would be much appreciated!
Shelter.joins(:pet => :type).where(:types => {exotic => false})
I believe it is impossible to get the results you want using just JOINS. Instead you need to find which shelters do have exotic pets and then negate that.
One way to accomplish that is through a subquery:
Shelter.where(<<~SQL)
NOT EXISTS (
SELECT 1 FROM pets
INNER JOIN types ON types.id = pets.type_id
WHERE shelters.id = pets.shelter_id
AND types.exotic IS TRUE
)
SQL
Of course that involves a lot of explicit SQL, something I don't mind, but others do not like it.
You can also do something similar using just the ActiveRecord query interface.
shelters_with_exotics = Shelter.joins(pets: :type).where(types: { exotic: true })
Shelter.where.not(id: shelters_with_exotics)
NOTE: The queries for the two examples are different. If it mattered you would need to benchmark both of them to determine which one performed best.
I have a product model setup like the following:
class Product < ActiveRecord::Base
has_many :product_atts, :dependent => :destroy
has_many :atts, :through => :product_atts
has_many :variants, :class_name => "Product", :foreign_key => "parent_id", :dependent => :destroy
end
And I want to search for products that have associations with multiple attributes.
I thought maybe this would work:
Product.joins(:product_atts).where(parent_id: params[:product_id]).where(product_atts: {att_id: [5,7]})
But this does not seem to do what I am looking for. This does where ID or ID.
So I tried the following:
Product.joins(:product_atts).where(parent_id: 3).where(product_atts: {att_id: 5}).where(product_atts: {att_id: 7})
But this doesn't work either, it returns 0 results.
So my question is how do I look for a model by passing in attributes of multiple join models of the same model type?
SOLUTION:
att_ids = params[:att_ids] #This is an array of attribute ids
product = Product.find(params[:product_id]) #This is the parent product
scope = att_ids.reduce(product.variants) do |relation, att_id|
relation.where('EXISTS (SELECT 1 FROM product_atts WHERE product_id=products.id AND att_id=?)', att_id)
end
product_variant = scope.first
This is a seemingly-simple request made actually pretty tricky by how SQL works. Joins are always just joining rows together, and your WHERE clauses are only going to be looking at one row at a time (hence why your expectations are not working like you expect -- it's not possible for one row to have two values for the same column.
There are a bunch of ways to solve this when dealing with raw SQL, but in Rails, I've found the simplest (not most efficient) way is to embed subqueries using the EXISTS keyword. Wrapping that up in a solution which handles arbitrary number of desired att_ids, you get:
scope = att_ids_to_find.reduce(Product) do |relation, att_id|
relation.where('EXISTS (SELECT 1 FROM product_atts WHERE parent_id=products.id AND att_id=?)', att_id)
end
products = scope.all
If you're not familiar with reduce, what's going on is it's taking Product, then adding one additional where clause for each att_id. The end result is something like Product.where(...).where(...).where(...), but you don't need to worry about that too much. This solution also works well when mixed with scopes and other joins.
I'm trying to list all the user's products with a probable association where a flag 'notification' is set to zero.
user.probable_associations.where(:notified => 0).collect{|a| Product.where(:id => a.product_id).collect{|p| p.name}}.to_sentence
It seems like using a where and collect method twice within the statement isn't very good. Is there a better way to go about this?
Also, the result is something like
"[\"Product A\"] and [\"Product B\"]"
which is pretty ugly...and I still need to remove the extra punctuation "[\" \"]
instead of something clean like
"Product A and Product B"
EDIT based on Rich's Answer, still have issues because notified is a field in associations NOT product:
has_many :probable_associations, -> { where "associations.category = 3"}, class_name: 'Association', before_add: :set_probable_category
has_many :probable_products, class_name: 'Product', through: :probable_associations, source: :product do
def not_notified
select(:name).where(notified: 0)
end
end
I'd use an ActiveRecord Association extension:
#app/models/user.rb
Class User < ActiveRecord::Base
has_many :products do
def not_notified
select(:name).where(notified: 0)
end
end
end
#-> #user.products.not_notified
That's my contribution, but you could then use #spickermann & #tompave's controbutions and use .flatten.to_sentence
Without knowing what probable_associations does would I rewrite the code to something like this:
product_ids = user.probable_associations.where(:notified => 0).map(&:product_id)
Product.where(:id => product_ids).map(&:name).to_sentence
Assuming that probable_associations is just an ActiveRecord has_many association, and that you want to end up with a list of titles for Product records, you can use this:
ids = user.probable_associations
.where(notified: 0)
.pluck(:product_id)
result = Product.where(id: ids).pluck(:name).to_sentence
It's similar to #spikermann's answer, but pluck(:column_name) is faster than using a block and only extracts the required column from the DB.
Also, the reason your code produces that string is that, by the time you call to_sentence, you have an Array of sub-arrays. Each sub-array contains a single element: a product name.
That's because the second collect is sent to an ActiveRecord::Relation containing just one record.
You could have solved that problem with flatten, but the whole operation could just be refactored.
I have the following models, each a related child of the previous one (I excluded other model methods and declarations for brevity):
class Course < ActiveRecord::Base
has_many :questions
scope :most_answered, joins(:questions).order('questions.answers_count DESC') #this is the query causing issues
end
class Question < ActiveRecord::Base
belongs_to :course, :counter_cache => true
has_many: :answers
end
class Answer < ActiveRecord::Base
belongs_to :question, :counter_cache => true
end
Right now I only have one Course populated (so when I run in console Course.all.count, I get 1). The first Course currently has three questions populated, but when I run Course.most_answered.count (most_answered is my scope method written in Course as seen above), I get 3 as the result in console, which is incorrect. I have tried various iterations of the query, as well as consulting the Rails guide on queries, but can't seem to figure out what Im doing wrong. Thanks in advance.
From what I can gather, your most_answered scope is attempting to order by the sum of questions.answer_count.
As it is there is no sum, and since there are three answers for the first course, your join on to that table will produce three results.
What you will need to do is something like the following:
scope :most_answered, joins(:questions).order('questions.answers_count DESC')
.select("courses.id, courses.name, ..., SUM(questions.answers_count) as answers_count")
.group("courses.id, courses.name, ...")
.order("answers_count DESC")
You'll need to explicitely specify the courses fields you want to select so that you can use them in the group by clause.
Edit:
Both places where I mention courses.id, courses.name, ... (in the select and the group), you'll need to replace this with the actual columns you want to select. Since this is a scope it would be best to select all fields in the courses table, but you will need to specify them individually.
I have a polymorphic association like this -
class Image < ActiveRecord::Base
has_one :approval, :as => :approvable
end
class Page < ActiveRecord::Base
has_one :approval, :as => :approvable
end
class Site < ActiveRecord::Base
has_one :approval, :as => :approvable
end
class Approval < ActiveRecord::Base
belongs_to :approvable, :polymorphic => true
end
I need to find approvals where approval.apporvable.deleted = false
I have tried something like this -
#approvals = Approval.find(:all,
:include => [:approvable],
:conditions => [":approvable.deleted = ?", false ])
This gives "Can not eagerly load the polymorphic association :approvable" error
How can the condition be given correctly so that I get a result set with approvals who's approvable item is not deleted ?
Thanks for any help in advance
This is not possible, since all "approvables" reside in different tables. Instead you will have to fetch all approvals, and then use the normal array methods.
#approvals = Approval.all.select { |approval| !approval.approvable.deleted? }
What your asking, in terms of SQL, is projecting data from different tables for different rows in the resultset. It is not possible to my knowledge.
So you'll have to be content with:
#approvals = Approval.all.reject{|a| a.approvable.deleted? }
# I assume you have a deleted? method in all the approvables
I would recommend either of the answers already presented here (they are the same thing) but I would also recommend putting that deleted flag into the Approval model if you really care to do it all in a single query.
With a polymorphic relationship rails can use eager fetching on the polys, but you can't join to them because yet again, the relationships are not known so the query is actually multiple queried intersected.
So in the end if you REALLY need to, drop into sql and intersect all the possible joins you can do to all the types of approvables in a single query, but you will have to do lots of joining manually. (manually meaning not using rails' built-in mechanisms...)
thanks for your answers
I was pretty sure that this couldn't be done. I wanted some more confirmation
besides that I was hoping for some other soln than looping thru the result set
to avoid performance related issues later
Although for the time being both reject/select are fine but in the long run I
will have to do those sql joins manually.
Thanks again for your help!!
M