In my rails app, I have a user model and a linkedin_connection model. Linkedin_connection belongs to user and user has_many linkedin_connections.
What's the best way to create a crossover array of connections between user1 and user2?
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I realized that this is sort of a different problem than I originally thought. I have 2 arrays of hashes. Each hash has an id element. How can I find the intersection of two hashes by their ids?
Example
user1.linkedin_connections => [{id: "123xyz", name: "John Doe"}, {id: "789abc", name: "Alexander Supertramp"}]
user2.linkedin_connections => [{id: "456ijk", name: "Darth Vader"}, {id: "123xyz", name: "John Doe"}]
cross_connections => [{id: "123xyz", name: "John Doe"}]
How can I calculate "cross_connections?"
Thanks!
What you want is the intersection of the two arrays. In ruby, that's easy, using the & operator:
crossover_connections = user1.linkedin_connections.to_a & user2.linkedin_connections.to_a
Related
Is there a way to count how many specific string value from the database column using Active Record (Using PostgreSQL as my database)?
If I wanted to show in my view the how many taco lovers there are in the world.
For example:
# Where the number "2" was an ActiveRecord count in the Persons table
# reading from the column named "favorite_food"
<div class="notice">
<p>There are 2 burrito lovers online</p>
</div>
From looking around the ActiveRecord documentation I got to this:
# == Schema Information
#
# Table name: Persons
#
# id :integer not null, primary key
# name :string default(""), not null
# age :integer default(""), not null
# favorite_food :string
# Data
# Person id: 1, name: "John", age: "18", favorite_food: "taco"
# Person id: 2, name: "Jane", age: "19", favorite_food: "taco"
# Person id: 3, name: "Bill", age: "20", favorite_food: "burrito"
# Person id: 4, name: "Beth", age: "21", favorite_food: "nacho"
# This will record total unique foods
Person.count(:favorite_food)
=> 3
# This will return a hash with total name of distinct foods
Person.group(:favorite_food).count
=> {taco=>"2", "burrito"=>1, "nacho"=>1}
I think the last bit is closer but I wanted to query a specific food type, how would I do this with ActiveRecord if this is possible? I was thinking I could iterate using enum but this would be not the best way to tackle this situation.
Thanks for taking the time to take a look at my question.
try this
Person.where(favorite_food: 'burrito').count
How do I fetch multiple attributes from a model instance, e.g.
Resource.first.attributes(:foo, :bar, :baz)
# or
Resource.where(foo: 1).fetch(:foo, :bar, :baz)
rather than returning all the attributes and selecting them manually.
You will use the method slice.
Slice a hash to include only the given keys. Returns a hash containing the given keys.
Your code will be.
Resource.first.attributes.slice("foo", "bar", "baz")
# with .where
Resource.where(foo: 1).select("foo, bar, baz").map(&:attributes)
How about pluck:
Resource.where(something: 1).pluck(:foo, :bar, :baz)
Which translates to the following SQL:
SELECT "resources"."foo", "resources"."bar" FROM, "resources"."baz" FROM "resources"
And returns an array of the specified column values for each of the records in the relation:
[["anc", 1, "M2JjZGY"], ["Idk", 2, "ZTc1NjY"]]
http://guides.rubyonrails.org/active_record_querying.html#pluck
Couple of notes:
Multiple value pluck is supported starting from Rails 4, so if you're using Rails 3 it won't work.
pluck is defined on ActiveRelation, not on a single instnce.
If you want the result to be a hash of attribute name => value for each record you can zip the results by doing something like the following:
attrs = [:foo, :bar, :baz]
Resource.where(something: 1).pluck(*attrs).map{ |vals| attrs.zip(vals).to_h }
To Fetch Multiple has_one or belongs_to Relationships, Not Just Static Attributes.
To fetch multiple relationships, such as has_one or belongs_to, you can use slice directly on the instance, use values to obtain just the values and then manipulate them with a map or collect.
For example, to get the category and author of a book, you could do something like this:
book.slice( :category, :author ).values
#=> #<Category id: 1, name: "Science Fiction", ...>, #<Author id: 1, name: "Aldous Huxley", ...>
If you want to show the String values of these, you could use to_s, like:
book.slice( :category, :author ).values.map( &:to_s )
#=> [ "Science Fiction", "Aldous Huxley" ]
And you can further manipulate them using a join, like:
book.slice( :category, :author ).values.map( &:to_s ).join( "➝" )
#=> "Science Fiction ➝ Aldous Huxley"
When I am creating multiple object of Factory using method create_list, the order and where method don't work on it because create_list creates the array of factory objects.
users = FactoryGirl.create_list(:user, 5)
users.order('name ASC')
It gives undefined method order for Array
So, what should I do to create the multiple factory objects inside the ActiveRecord Collection?
The order and where methods are not defined on Array but on ActiveRecord::Relation. It's the kind of thing that gets passed around by the ActiveRecord query interface. You simply cannot run a query on an array. To run a query you need to start from scratch:
create_list, :user, 5
users = User.where(...).order(name: :asc)
But you might as well directly pass your arguments to create_list so that the condition is satisfied without needing to re-select the users. I also often find myself writing arrays explicitly when I need to alter values in each row e. g.
users = [
create(:user, name: 'Alfred'),
create(:user, name: 'Bob'),
create(:user, name: 'Charlie'),
create(:user, name: 'David'),
create(:user, name: 'Egon')
]
The users are already ordered by name and you're good to go. If you have some condition in the where clause that for example separates the users in two groups, you can just go ahead and separate these users directly. For example imagine we have an admin flag in the users table and you want to create many users, some being admins and some not. Then you'd do
admins = [
create(:user, name: 'Alfred', admin: true),
create(:user, name: 'Charlie', admin: true),
create(:user, name: 'Egon', admin: true)
]
visitors = [
create(:user, name: 'Bob'),
create(:user, name: 'David')
]
No need to query at all. Of course you can also do that in let syntax if you like.
I have used code in a controller to update all records for a different model using an array of ids:
Expense.update_all({reimbursed: true}, {id: params[:expense_ids]})
Is there a way to new/build/create records?
Something like:
Expense.new_all({reimbursed: true}, {expense_id: params[:expense_ids]})
Thanks for your help!
You can pass multiple attribute hashes to create to create multiple instances of the model. From the docs:
# Create an Array of new objects
User.create([{ first_name: 'Jamie' }, { first_name: 'Jeremy' }])
Suppose I have Users data that store array of pet in String datatype
[
#<User id: 1, name: "John", pets: "---\n- cat\n- dog\n- bunny\n- ''\n">,
#<User id: 2, name: "Pete", pets: "---\n- dog\n- bunny\n- ''\n">,
#<User id: 3, name: "Jack", pets: "---\n- cat\n- ''\n">,
#<User id: 4, name: "Kurt", pets: "---\n- cat\n- bunny\n- ''\n">
]
Can i get all users that has a cat? Maybe something like User.find_all_by... or User.where(....) or anything that return as a relation? So i can order with active record query.
I know i can get all users that has a cat with
User.all.select{|s| YAML.load(s.pets).include?'cat'}
, but it convert to array that cannot be ordered with active record query.
thx for helping.
You could use simple SQL to see if 'cat' shows up in the serialized column.
User.where('pets LIKE "%cat%"').all
You need to normalize your data, add Pet model and set has_and_belongs_to_many association between theese models.