This question is based on this: Rails, why joins returns array with non-uniq values?
Let say I get non uniq array by .joins() method:
City.joins(:locations)
# => [#<City id: 5, name: "moscow", created_at: "2010-07-02 15:09:16", updated_at: "2010-07-02 15:09:16">, #<City id: 5, name: "moscow", created_at: "2010-07-02 15:09:16", updated_at: "2010-07-02 15:09:16">, #<City id: 5, name: "moscow", created_at: "2010-07-02 15:09:16", updated_at: "2010-07-02 15:09:16">, #<City id: 5, name: "moscow", created_at: "2010-07-02 15:09:16", updated_at: "2010-07-02 15:09:16">]
I can make records uniq by using
City.joins(:locations).group('cities.id') # or simpler
City.joins(:locations).uniq
# => [#<City id: 5, name: "moscow", created_at: "2010-07-02 15:09:16", updated_at: "2010-07-02 15:09:16">]
How can I make .joins() method returns uniq records by default?
You could try overriding the .joins method for the models you need, but I would suggest just writing a scope, e.g.
scope :unique_locations, -> { joins(:locations).uniq }
Then just call City.unique_locations. It's cleaner and more readable that way.
Generally overwriting methods should be done only when you're sure you won't need it 'the old way', and it makes sense. Plus, when you say City.joins(:locations) the reader expects default behaviour, and returning something else will cause chaos and confusion.
You can define has_many macro, with the stubby lambda as an argument:
has_many :locations, -> { joins(:locations).uniq }
Also you can define own AR relation method, it stil use a simple has_many macro.
has_many :locations do
def only_uniq
joins(:locations).uniq
end
end
Now use it:
c = City.find(123)
c.locations.only_uniq
It does the same thing as scope or lambda in has_many.
Related
I'm new in ruby rails and face some difficult to achieve something.
Now I have a product model:
class Product < ApplicationRecord
belongs_to :category
And category model:
class Category < ApplicationRecord
has_many :products
When I call the product like so: #products.inspect i wan to see the category belongs to the product. My output now looks like so:
<ActiveRecord::Relation [#<Product id: 1, name: "Adidas", description: "Adidas is a Dutch multinational corporation that i...", price: 100, created_at: "2022-08-23 10:02:11.110159000 +0000", updated_at: "2022-08-23 10:02:11.114384000 +0000", category_id: 1>, #<Product id: 2, name: "asd", description: "12easd", price: 12, created_at: "2022-08-24 09:35:38.839809000 +0000", updated_at: "2022-08-24 09:35:38.847999000 +0000", category_id: 1>]>
Getting the product.category working fine, but, I need also the name of the category attached to this output. I need this because the product is sent to a JavaScript function and I need to call the category name from there.
What I already try is the follow:
def index
#products = Product.includes(:category).all
end
Thanks in advance.
I found it!
#product.to_json(include: :category)
And now I get the related category model
The following tag in a nested form
<%= check_box_tag "friend_ids[]", ff.id, #contentrestrictions.friends.include?(ff.id) %>
is handling the following array of records
>> #contentrestrictions
[
#<Contentrestriction id: 29, usercontent_id: nil, friend_id: nil, created_at: "2019-04-28 10:55:32", updated_at: "2019-04-28 10:55:32">,
#<Contentrestriction id: 30, usercontent_id: nil, friend_id: 2, created_at: "2019-04-28 10:55:32", updated_at: "2019-04-28 10:55:32">,
#<Contentrestriction id: 31, usercontent_id: nil, friend_id: 4, created_at: "2019-04-28 10:55:32", updated_at: "2019-04-28 10:55:32">]
Even though
class Contentrestriction < ApplicationRecord
belongs_to :friend, optional: true
#contentrestrictions. followed by any of friend_id, friend_ids both appended with or without [] all lead to NoMethodError: undefined method for Array.
how can this include function get a proper array to work with?
the issue is in this line:
#contentrestrictions.friends.include?(ff.id)
you are comparing a friend object with a friend id, you could use pluck to get the friend ids, or you could just compare the objects:
#contentrestrictions.friends.include?(ff)
this will make a query for the .friends and you could remove this query by pre-loading the friends association, e.g. eager_load(:friends) or includes(:friends)
Let's work with these classes:
class User < ActiveRecord::Base
has_many :project_participations
has_many :projects, through: :project_participations, inverse_of: :users
end
class ProjectParticipation < ActiveRecord::Base
belongs_to :user
belongs_to :project
enum role: { member: 0, manager: 1 }
end
class Project < ActiveRecord::Base
has_many :project_participations
has_many :users, through: :project_participations, inverse_of: :projects
end
A user can participate in many projects with a role as a member or a manager. The connecting model is called ProjectParticipation.
I now have a problem using the associations on unsaved objects. The following commands work like I think they should work:
# first example
u = User.new
p = Project.new
u.projects << p
u.projects
=> #<ActiveRecord::Associations::CollectionProxy [#<Project id: nil>]>
u.project_participations
=> #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil>]>
So far so good - AR created the ProjectParticipation by itself and I can access the projects of a user with u.projects.
But it does not work if I create the ProjectParticipation by myself:
# second example
u = User.new
pp = ProjectParticipation.new
p = Project.new
pp.project = p # assign project to project_participation
u.project_participations << pp # assign project_participation to user
u.project_participations
=> #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil>]>
u.projects
=> #<ActiveRecord::Associations::CollectionProxy []>
Why are the projects empty? I cannot access the projects by u.projects like before.
But if I go through the participations directly, the project shows up:
u.project_participations.map(&:project)
=> [#<Project id: nil>]
Shouldn't it work like the first example directly: u.projects returning me all projects not depending on whether I create the join object by myself or not? Or how can I make AR aware of this?
Short answer: No, second example won't work the way it worked in first example. You must use first example's way of creating intermediate associations directly with user and project objects.
Long answer:
Before we start, we should know how has_many :through is being handled in ActiveRecord::Base. So, let's start with has_many(name, scope = nil, options = {}, &extension) method which calls its association builder here, at the end of method the returned reflection and then add reflection to a hash as a cache with key-value pair here.
Now question is, how do these associations gets activated?!?!
It's because of association(name) method. Which calls association_class method, which actually calls and return this constant: Associations::HasManyThroughAssociation, that makes this line to autoload active_record/associations/has_many_through_association.rb and instantiate its instance here. This is where owner and reflection are saved when the association is being created and in the next reset method is being called which gets invoked in the subclass ActiveRecord::Associations::CollectionAssociation here.
Why this reset call was important? Because, it sets #target as an array. This #target is the array where all associated objects are stored when you make a query and then used as cache when you reuse it in your code instead of making a new query. That's why calling user.projects(where user and projects persists in db, i.e. calling: user = User.find(1) and then user.projects) will make a db query and calling it again won't.
So, when you make a reader call on an association, e.g.: user.projects, it invokes the collectionProxy, before populating the #target from load_target.
This is barely scratching the surface. But, you get the idea how associations are being build using builders(which creates different reflection based on the condition) and creates proxies for reading data in the target variable.
tl;dr
The difference between your first and second examples is the way their association builders are being invoked for creating associations' reflection(based on macro), proxy and target instance variables.
First example:
u = User.new
p = Project.new
u.projects << p
u.association(:projects)
#=> ActiveRecord::Associations::HasManyThroughAssociation object
#=> #proxy = #<ActiveRecord::Associations::CollectionProxy [#<Project id: nil, name: nil, created_at: nil, updated_at: nil>]>
#=> #target = [#<Project id: nil, name: nil, created_at: nil, updated_at: nil>]
u.association(:project_participations)
#=> ActiveRecord::Associations::HasManyAssociation object
#=> #proxy = #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil, created_at: nil, updated_at: nil>]>
#=> #target = [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil, created_at: nil, updated_at: nil>]
u.project_participations.first.association(:project)
#=> ActiveRecord::Associations::BelongsToAssociation object
#=> #target = #<Project id: nil, name: nil, created_at: nil, updated_at: nil>
Second example:
u = User.new
pp = ProjectParticipation.new
p = Project.new
pp.project = p # assign project to project_participation
u.project_participations << pp # assign project_participation to user
u.association(:projects)
#=> ActiveRecord::Associations::HasManyThroughAssociation object
#=> #proxy = nil
#=> #target = []
u.association(:project_participations)
#=> ActiveRecord::Associations::HasManyAssociation object
#=> #proxy = #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil, created_at: nil, updated_at: nil>
#=> #target = [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil, created_at: nil, updated_at: nil>]
u.project_participations.first.association(:project)
#=> ActiveRecord::Associations::BelongsToAssociation object
#=> #target = #<Project id: nil, name: nil, created_at: nil, updated_at: nil>
There's no proxy for BelongsToAssociation, it has just target and owner.
However, if you are really inclined to make your second example work, you will just have to do this:
u.association(:projects).instance_variable_set('#target', [p])
And now:
u.projects
#=> #<ActiveRecord::Associations::CollectionProxy [#<Project id: nil, name: nil, created_at: nil, updated_at: nil>]>
In my opinion which is a very bad way of creating/saving associations. So, stick with the first example itself.
This is more of a rails structure thing at the level of the ruby data structures.
To simplify it lets put it this way.
First of all imagine User as a data structure contains:
project_participations Array
projects Array
And Project
users Array
project_participations Array
Now when you mark a relation to be :through another (user.projects through user.project_participations)
Rails implies that when you add a record to that first relation (user.projects) it will have to create another one in the second realation (user.project_participations) that is all the effect of the 'through' hook
So in this case,
user.projects << project
#will proc the 'through'
#user.project_participations << new_entry
Keep in mind that the project.users is still not updated because its a completely different data structure and you have no reference to it.
So lets take a look what will happen with the second example
u.project_participations << pp
#this has nothing hooked to it so it operates like a normal array
So In conclusion, this acts like a one way binding on a ruby data structure level and whenever you save and refresh your objects, this will behave the way you wanted.
At the risk of some serious oversimplification let me try to explain what is going on
What Most of the other answers are trying to tell you is that these objects have not been linked yet by active record until they are persisted in the DB. Consequently the association behavior that you are expecting is not fully wired up.
Notice that this line from your first example
u.project_participations
=> #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil>]>
Is identical to the result from your second example
u.project_participations
=> #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil>]>
This statement from your analysis of what you think rails is doing is inaccurate:
So far so good - AR created the ProjectParticipation by itself and I
can access the projects of a user with u.projects.
AR record has not created the ProjectParticipation. You have declared this relationship in your model. AR is just returning proxy for the collection that it will have at some point in the future, which when populated assigned, etc, you will be be able to iterate over and query its members etc.
The reason that this works:
u.projects << p
u.projects
=> #<ActiveRecord::Associations::CollectionProxy [#<Project id: nil>]>
But this doesn't
pp.project = p # assign project to project_participation
u.project_participations << pp # assign project_participation to user
u.project_participations
=> #<ActiveRecord::Associations::CollectionProxy [#<ProjectParticipation id: nil, user_id: nil, project_id: nil, role: nil>]>
u.projects
=> #<ActiveRecord::Associations::CollectionProxy []>
Is that in the first case you are just adding objects to an array that your user instance has direct access to. In the second example the has_many_through relationship reflects a relationship that happens at the database level. In the second example in order for the your projects to be accessible through your user, AR has to actually run a query that joins the tables and returns the data you are looking for. Since none of these objects is persisted yet that database query can't happen yet so all you get back are the proxies.
The last bit of code is misleading because it is not actually doing what you think.
u.project_participations.map(&:project)
=> [#<Project id: nil>]
In this case you have a user which is directly holding an array of ProjectParticipations one of which is directly holding a project so it works. It is not actually using the has_many_through mechanism in they way you think.
Again this is a bit of an oversimplification but that is the general idea.
Associations are defined on database level and make use of database table's primary key (and in polymorphic cases, class name). In case of has_many :through the lookup on association (say, User's Projects) is:
Fetch all User-Project pairs, whose user_id is a certain value (primary key of an existing User in the database)
Fetch all project_id (primary keys of projects) from these pairs
Fetch all Projects by resulting keys
Of course, these are simple terms, in database terms it's much shorter and uses more complicated abstractions, such as an inner join, but the essence is the same.
When you create a new object via new, it is not yet saved in the database, and therefore has no primary key (it's nil). That said, if the object is not in a database yet, you have no way of referencing it from any ActiveRecord's association.
Side note:
There is a possibility, however, that a newly created (and not saved yet) object will act as if something is associated with it: it might show entries belonging to NULL. This usually means you have an error in your database schema that allows such things to happen, but hypothetically, one could design his database to make use of this.
I'm trying to do something fairly simple. I have two models, User and Group. For simplicity's sake, let's say they look like this:
class User < ActiveRecord::Base
has_and_belongs_to_many :groups
end
and
class Group < ActiveRecord::Base
has_and_belongs_to_many :users
end
Now, for some reason, I have a user that has the same group twice. In the Rails Console:
user = User.find(1000)
=> #<User id: 1000, first_name: "John", last_name: "Doe", active: true, created_at:
"2013-01-02 16:52:36", updated_at: "2013-06-17 16:21:09">
groups = user.groups
=> [#<Group id: 1, name: "student", is_active: true, created_at: "2012-12-24 15:08:59",
updated_at: "2012-12-24 15:08:59">, #<Group id: 1, name: "student", is_active: true,
created_at: "2012-12-24 15:08:59", updated_at: "2012-12-24 15:08:59">]
user.groups = groups.uniq
=> [#<Group id: 1, name: "student", is_active: true, created_at: "2012-12-24 15:08:59",
updated_at: "2012-12-24 15:08:59">]
user.save
=> true
And there is some SQL output that I've silenced. I would think that everything should be all set, but it's not. The groups aren't updated, and that user still has both. I could go into the join table and manually remove the duplicates, but that seems cludgy and gross and unnecessary. What am I doing wrong here?
I'm running Rails 3.2.11 and Ruby 1.9.3p392
Additional note: I've tried this many different ways, including using user.update_attributes, and using group_ids instead of the groups themselves, to no avail.
The reason this doesn't work is because ActiveRecord isn't handling the invalid state of duplicates in the habtm association (or any CollectionAssociation for that matter). Any ids not included in the newly assigned array are deleted - but there aren't any in this case. The relevant code:
# From lib/active_record/associations/collection_association.rb
def replace_records(new_target, original_target)
delete(target - new_target)
unless concat(new_target - target)
#target = original_target
raise RecordNotSaved, "Failed to replace #{reflection.name} because one or more of the " \
"new records could not be saved."
end
target
end
The 'targets' being passed around are Arrays of assigned records. Note the call to delete(target - new_target) is equivalent in your case to delete(user.groups - user.groups.uniq) which results in an empty Array passed (since comparison is based on the id attribute of each record).
Instead, you'll need to clear out the association and then reassign the single group again:
group = user.groups.first
user.groups.clear
user.groups << group
This might be a way to cleanup those duplicates (it handles any number of groups of duplicate associations):
user = User.find(1000)
user.groups << user.groups.group_by(&:id).values.find_all {|v| v.size > 1}.each {|duplicates| duplicates.uniq_by! {|obj| obj.id}}.flatten.each {|duplicate| user.groups.delete(duplicate)}
I have a ActiveRecord query for example like this:
#result = stuff.limit(10)
where stuff is a active record query with where clauses, order by, etc...
Now I thought why to pass magic numbers like that to the controller? So do you think is it a good practice to define a scope for "limit(10)" and use that instead? and how would the syntax look like?
There are indeed multiple ways of doing such, class methods are one as pointed out by #Dave Newton. If you'd like to use scopes, here's how:
scope :max_records, lambda { |record_limit|
limit(record_limit)
}
Or with the Ruby 1.9 "stabby" lambda syntax and multiple arguments:
scope :max_records, ->(record_limit, foo_name) { # No space between "->" and "("
where(:foo => foo_name).limit(record_limit)
}
If you'd like to know the deeper differences between scopes and class methods, check out this blog post.
Hope it helps. Cheers!
Well Scopes are meant for this
Scoping allows you to specify commonly-used Arel queries which can be referenced as method calls on the association objects or models. With these scopes, you can use every method previously covered such as where, joins and includes. All scope methods will return an ActiveRecord::Relation object which will allow for further methods (such as other scopes) to be called on it.
Source: http://guides.rubyonrails.org/active_record_querying.html#scopes
So if you feel that there are some common queries which you have, or you need some kind of chaining in your queries which are common to many. Then i will suggest you to go for scopes to prevent repetition.
Now to answer how the scope will look like in your case
class YourModel < ActiveRecord::Base
scope :my_limit, ->(num) { limit(num)}
scope :your_where_condition, ->(num) { where("age > 10").mylimit(num) }
end
Pass parameters in Rails scope
Definition of scope
scope :name_of_scope, ->(parameter_name) {condition whatever you want to put in scope}
Calling Method
name_of_scope(parameter_name)
The scope would look like any other (although you may prefer a class method), e.g.,
class Stuff < ActiveRecord::Base
def self.lim
limit(3)
end
end
> Stuff.lim.all
=> [#<Stuff id: 1, name: "foo", created_at: "2013-03-01 17:58:32", updated_at: "2013-03-01 17:58:32">,
#<Stuff id: 2, name: "bnar", created_at: "2013-03-01 17:58:32", updated_at: "2013-03-01 17:58:32">,
#<Stuff id: 3, name: "baz", created_at: "2013-03-01 17:58:32", updated_at: "2013-03-01 17:58:32">]
> Stuff.all.length
=> 8
If you always (or "almost" always) want that limit, use a default scope:
class Stuff < ActiveRecord::Base
attr_accessible :name, :hdfs_file
default_scope limit(3)
end
> Stuff.all
=> [#<Stuff id: 1, name: "foo", created_at: "2013-03-01 17:58:32", updated_at: "2013-03-01 17:58:32">,
#<Stuff id: 2, name: "bnar", created_at: "2013-03-01 17:58:32", updated_at: "2013-03-01 17:58:32">,
#<Stuff id: 3, name: "baz", created_at: "2013-03-01 17:58:32", updated_at: "2013-03-01 17:58:32">]
> Stuff.all.length
=> 3
To skip the default scope:
> Stuff.unscoped.all.size
=> 8
Scope in Rails model with parameter:
scope :scope_name, -> (parameter, ...) { where(is_deleted: parameter, ...) }
Or:
scope :scope_name, lambda{|parameter, ...| where(is_deleted:parameter, ...)}