class Event
has_many :keywords, :through => :event_keywords
end
class User
has_many :keywords, :through => :user_keywords
end
I have a User method that calculates an event's relevance based on the keywords it shares with a specific user:
User.rb
def calculate_event_relevance(event_id)
event_keywords = event.keywords
event_keywords.each do |kw|
user_keyword_match = self.keywords.where(id: kw.id).first
if user_keyword_match
## do some stuff
end
end
end
Right now, I am looping through each keyword. In the loop, I make a query to see if the user also has that keyword.
Is there a way instead to make one single query (and save it to event_keywords) that only returns the event.keywords that a user also has so that I don't need to loop through all of them?
Is there a query that can find which keywords a user and event have in common?
Assuming that event_keywords and user_keywords are both arrays, you can use the & on the array to get the values that are present in both.
For example,
[1,2,3,4,5,9] & [5,6,7,8,9] #=> [5, 9]
In this case, 5 and 9 are present in both arrays so they are returned as a result.
In your case, you can do something like
share_keywords = event.keywords & self.keywords
To return an array with all the keywords shared between event and user. Then you can iterate through that and do what you need to do.
Related
Let's say I have a User model. User has 2 has_many associations, that is User has many pencils and has many cars. Cars and Pencils table has same attribute, :date, and separate such as :speed(car) and :length(pencil). I want to join a user's pencils and cars on their common attribute, :date, so that I have an array/relation [:date, :speed, :length]. How do I achieve that, I tried joins and merge but they were no use.
I'd definitely recommend getting this into a query rather than a loop, for efficiency's sake. I think this will work:
Car.joins(:user => :pencils).where("pencils.date = cars.date")
And if you want to reduce it to the array immediately:
Car.joins(:user => :pencils).where("pencils.date = cars.date").pluck("cars.date", "cars.speed", "pencils.length")
If you need to include matches where date is nil, you might need to add:
Car.joins(:user => :pencils).where("(pencils.date = cars.date) OR (pencils.date IS NULL AND cars.date IS NULL)")
Many more efficient options exist, but here is one possible approach:
class User < ActiveRecord::Base
def get_merged_array
dates = (cars.map(&:date) & pencils.map(&:date))
results = []
dates.each do |date|
cars.where(date: date).each do |car|
pencils.where(date: date).each do |pencil|
results << [date, car.speed, pencil.length]
end
end
end
results
end
end
I have a program i am making changes to for my work. I know what i must do but i am having problems getting the code to work. I come from a Java and C background.
i have two tables one table called customprojecschedule_lines has a project_id,workorder_base_id, and other various columns column.
The other table called customschedule has an id, workorder column and various other columns.
I have a method and variable called work order.
I am trying to get an SQL statement that will do that like this:
class Customschedule < ActiveRecord::Base
set_table_name "customschedules"
after_create :build_customprojectschedule_lines
has_many :customprojectschedule_lines, :dependent => :destroy
has_one :projectschedule_cost
delegate :est_cost, :act_cost, :to => :projectschedule_cost, :allow_nil => true
attr_accessor :workorder_base, :lots
def workorder
customschedule.where(:id => customprojectschedule_lines.product_id)
end
def workorder=(wo)
#workorder_base = wo
customprojectschedule_lines.each do |pl|
pl.update_attributes({:workorder_base_id => wo})
end
end
def build_customprojectschedule_lines
lines = #lots.split(',').inject([]) do |lines, lot_id|
line = customprojectschedule_lines.find_or_initialize_by_workorder_lot_id(lot_id)
if line.new_record?
p workorder_base
line.workorder_base_id = #workorder_base
line.line_no = lot_id
line.workorder_split_id = 0
end
lines << line
end
customprojectschedule_lines.replace(lines)
end
Basically what i would like is that whenever a user enters a workorder on the form number goes into the database gets the stored values with that record and then retrieves the ID(from that record) and puts that same id in my other table.
However, i keep getting this error:
undefined local variable or method `customschedule' for #
<Customschedule:0x00000005542040>
Before when i was trying things i kept getting a weird looking select statement saying that Customschedule ID was null.
We use oracle here.
This is my first time posting on here so please let me know if i need anything else.
Any help is greatly appreciated.
I think all you need is to upcase the first letter in this line
customschedule.where(:id => customprojectschedule_lines.product_id)
change it to
Customschedule.where(:id => customprojectschedule_lines.product_id)
How do I convert to JSON and back and keep the relationships? It thinks they don't exist when I un-parcel the object!
irb(main):106:0* p = Post.last
=> #<Post ...
irb(main):107:0> p.tags
=> #<ActiveRecord::Associations::CollectionProxy [#<Tag id: 41, ...
irb(main):109:0* p.tags.count
=> 2 #### !!!!!!!!!!!!
irb(main):110:0> json = p.to_json
=> "{\"id\":113,\"title\":... }"
irb(main):111:0> p2 = Post.new( JSON.parse(json) )
=> #<Post id: 113, title: ...
irb(main):112:0> p2.tags
=> #<ActiveRecord::Associations::CollectionProxy []>
irb(main):113:0> p2.tags.count
=> 0 #### !!!!!!!!!!!!
Here is the model
class Post < ActiveRecord::Base
has_many :taggings, :dependent => :destroy
has_many :tags, :through => :taggings
What someone suggested, but doesn't work
irb(main):206:0* Post.new.from_json p.to_json(include: :tags)
ActiveRecord::AssociationTypeMismatch: Tag(#60747984) expected, got Hash(#15487524)
I simulated the exact same scenario like yours and found out:
Whenever a model(Post) has a has_many through association then upon creating an instance of that Model i.e., Post passing a Hash for eg: Post.new( JSON.parse(json) ) or Post.new(id: 113) seems like Rails treats them differently although they are pointing to the same record.
I ran the following commands in the sequence as given below:
p = Post.last
p.tags
p.tags.count
json = p.to_json
p2 = Post.new( JSON.parse(json) )
p2.tags
p2.tags.count ## Gives incorrect count
p3 = Post.find(JSON.parse(json)["id"]) ### See notes below
p3.tags
p3.tags.count ## Gives the correct count
Instead of creating a new instance of Post using Hash directly, I fetched the record from database using the id obtained from deserializing json. In this case, the instance p3 and instance p2 refer to the same Post but Rails is interpreting them differently.
Disclaimer: This is not, in any way, an ideal solution (and I would call it down-right cheesy), but its about the only thing I've been able to come up with for your scenario.
What Kirti Thorat said is correct; when you have a dependent object, Rails expects the association in the hash to be of that specific class (in your case, a Tag object). Hence the error you're getting: Tag expected...got Hash.
Here comes the cheesy part: One way to properly deserialize a complex object is to leverage the accepts_nested_attributes_for method. By using this method, you'll allow your Post class to properly deserialize the dependent Tag key-value pairs to proper Tag objects. Start with this:
class Post < ActiveRecord::Base
accepts_nested_attributes_for :tags
# rest of class
end
Since accepts_nested_attributes_for searches for a key with the word _attributes for the given association, you'll have to alter the JSON when it is rendered to accommodate this by overriding the as_json method in your Post class, like so:
def as_json(options={})
json_hash = super.as_json(options)
unless json_hash["tags"].nil?
json_hash["tags_attributes"] = json_hash["tags"] # Renaming the key
json_hash.delete("tags") # remove the now unnecessary "tags" key
end
json_hash # don't forget to return this at the end
end
Side note: There are lots of json building gems such as acts_as_api that will allow you to remove this as_json overriding business
So now your rendered JSON has all the Post attributes, plus an array of tag attribute key-value pairs under the key tags_attributes.
Technically speaking, if you were to deserialize this rendered JSON in the manner suggested by Kirti, it would work and you would get back a properly populated active record object. However, unfortunately, the presence of the id attributes in both the parent Post object, and the dependent tag objects means that active record will fire off at least one SQL query. It will do a quick lookup for the tags to determine if anything needs to be added or deleted, as per the specifications of the has_many relationship (specifically, the collection=objects part).
Since you said you'd like to avoid hitting the database, the only solution I've been able to find is to render to JSON in the same way leesungchul suggested, but specifically excluding the id fields:
p_json = p.to_json(except: [:id], include: {tags: {except: :id}})
If you then do:
p2 = Post.new(JSON.parse(p_json))
You should get back a fully rendered Post object without any DB calls.
This, of course, assumes you don't need those id fields. In the event you do...frankly I'm not certain of a better solution other than to rename the id fields in the as_json method.
Also note: With this method, because of the lack of id fields, you won't be able to use p2.tags.count; it will return zero. You'll have to use .length instead.
You can try
p2.as_json( :include => :tags )
When you call
p2.tags
you get correct tags but p2 is not saved in the database yet. This seems the reason for
p2.tags.count
giving a 0 all the time.
If you actually do something like:
p2.id = Post.maximum(:id) + 1
p2.tags #Edit: This needs to be done to fetch the tags mapped to p from the database.
p2.save
p2.tags.count
You get the correct count
Really been struggling trying to get a group by to work when I have to join to another table. I can get the group by to work when I don't join, but when I want to group by a column on the other table I start having problems.
Tables:
Book
id, category_id
Category
id, name
ActiveRecord schema:
class Category < ActiveRecord::Base
has_many :books
end
class Book < ActiveRecord::Base
belongs_to :category
end
I am trying to get a group by on a count of categories. I.E. I want to know how many books are in each category.
I have tried numerous things, here is the latest,
books = Book.joins(:category).where(:select => 'count(books.id), Category.name', :group => 'Category.name')
I am looking to get something back like
[{:name => fiction, :count => 12}, {:name => non-fiction, :count => 4}]
Any ideas?
Thanks in advance!
How about this:
Category.joins(:books).group("categories.id").count
It should return an array of key/value pairs, where the key represents the category id, and the value represents the count of books associated with that category.
If you're just after the count of books in each category, the association methods you get from the has_many association may be enough (check out the Association Basics guide). You can get the number of books that belong to a particular category using
#category.books.size
If you wanted to build the array you described, you could build it yourself with something like:
array = Categories.all.map { |cat| { name: cat.name, count: cat.books.size } }
As an extra point, if you're likely to be looking up the number of books in a category frequently, you may also want to consider using a counter cache so getting the count of books in a category doesn't require an additional trip to the database. To do that, you'd need to make the following change in your books model:
# books.rb
belongs_to :category, counter_cache: true
And create a migration to add and initialize the column to be used by the counter cache:
class AddBooksCountToCategories < ActiveRecord::Migration
def change
add_column :categories, :books_count, :integer, default: 0, null: false
Category.all.each do |cat|
Category.reset_counters(cat.id, :books)
end
end
end
EDIT: After some experimentation, the following should give you close to what you want:
counts = Category.joins(:books).count(group: 'categories.name')
That will return a hash with the category name as keys and the counts as values. You could use .map { |k, v| { name: k, count: v } } to then get it to exactly the format you specified in your question.
I would keep an eye on something like that though -- once you have a large enough number of books, the join could slow things down somewhat. Using counter_cache will always be the most performant, and for a large enough number of books eager loading with two separate queries may also give you better performance (which was the reason eager loading using includes changed from using a joins to multiple queries in Rails 2.1).
How can I write an AR find query to have the results ordered by the number of records in a has_many association?
class User < ActiveRecord::Base
has_many :photos
end
I want to do something like...
User.find(:all, :order => photos.count)
I realize my find is not valid code. Say I have the following data.
User 1, which has 3 photos
User 2, which has 5 photos
User 3, which has 2 photos
I want my find to bring me back the users in the order of...
User 2,
User 1,
User 3
based on the count of of the users photos
The easiest way to achieve this is probably to add a counter cache to that model and then sort by that column.
class Photo < ActiveRecord::Base
belongs_to :user, :counter_cache => true
end
And be sure to add a column to your users table called photos_count.
Then you will be able to...
User.find(:all, :order => 'photos_count')
If you don't want an extra column, you could always ask for an extra column in the returned result set:
User.all(:select => "#{User.table_name}.*, COUNT(#{Photo.table_name}.id) number_of_photos",
:joins => :photos,
:order => "number_of_photos")
This generates the following SQL:
SELECT users.*, COUNT(photos.id) number_of_photos
FROM `users` INNER JOIN `photos` ON photos.user_id = users.id
ORDER BY number_of_photos
If you don't want to add a counter cache column, your only option is to sort after the find. If you :include the association in your find, you won't incur any additional database work.
users = User.find(:all, :include => :photos).sort_by { |u| -u.photos.size }
Note the negative sign in the sort_by block to sort from high to low.
I would advise you not to write direct SQL, since implementations of it may vary from store to store. Fortunately, you have arel:
User.joins(:photos).group(Photo.arel_table[:user_id]).
order(Photo.arel_table[:user_id].count)
Counter cache will help, but you'll need an extra column in the db.
I'd add this as a comment on the top answer, but I can't for some reason. According to this post:
http://m.onkey.org/active-record-query-interface
The User.all(options) method will be deprecated after Rails 3.0.3, and replaced with a bunch of other (handy, chainable) active record type stuff, but it makes it very hard to figure out how to put together the same kind of query.
As a result, I've gone ahead and implemented the counter cache method. This was pretty easy and painless with the exception that you need to remember to update the column information in your migration, otherwise all existing records will have "0."
Here's what I used in my migration:
class AddUserCountToCollections < ActiveRecord::Migration
def self.up
add_column :collections, :collectionusers_count, :integer, :default => 0
Collection.reset_column_information
Collection.all.each do |c|
Collection.update_counters c.id, :collectionusers_count => c.collectionusers.count
end
end
def self.down
remove_column :collections, :collectionusers_count
end
end
In theory this should be faster, too. Hope that's helpful going forward.
Your question doesn't make sense. The :order parameter specifies a column name and an optional ordering direction i.e. asc(ending) or desc(ending).
What is the result that you're trying to achieve?