I use rails 4.1 with Postgres and I have a model like this one:
class User < ActiveRecord::Base
has_many :events
has_many :event_memberships
has_many :shared_events, through: :event_memberships, source: event
def all_events
#... code goes here
end
end
I'd like to do an union between events and shared_events associations but I can't make it work.
The only thing I can make it work is this:
def all_events
events + shared_events
end
But it will execute 2 SQL queries instead of one and I won't be able to order or limit the results.
I have also tried something like this:
def all_events
User.find_by_sql("(#{events.to_sql}) UNION (#{shared_events.to_sql})")
end
Or this method https://coderwall.com/p/9hohaa
But both methods throw this error:
PG::UndefinedParameter: ERROR: there is no parameter $1
That seems to be known bug in rails 4+ and it won't be resolved https://github.com/rails/rails/issues/13686
So my only option here seems to write plain old SQL.
Anyone with a better idea ?
Related
In my application I have models Post & Slides & I have:
class Post < ActiveRecord::Base
has_many :slides, inverse_of: :post
accepts_nested_attributes_for :slides, reject_if: :all_blank, allow_destroy: true
Everything works fine, only thing I need (because of how my application will work), is when a slide is created, I need to assign it to current_user or user that is creating the record.
I already have user_id in my slides table and:
class User < ActiveRecord::Base
has_many :posts
has_many :slide
end
class Slide < ActiveRecord::Base
belongs_to :user
belongs_to :post
end
My PostsController looks like this:
def new
#post = current_user.posts.build
// This is for adding a slide without user needing to click on link_to_add_association when they enter new page/action
#post.slides.build
end
def create
#post = current_user.posts.build(post_params)
respond_to do |format|
if #post.save
format.html { redirect_to #post, notice: 'Was successfully created.' }
else
format.html { render :new }
end
end
end
Any help is appreciated!
There are two ways to accomplish this:
First option: when saving the slide, fill in the user-id, but this will get pretty messy quickly. You either do it in the model in a before_save, but how do you know the current-user-id? Or do it in the controller and change the user-id if not set before saving/after saving.
There is, however, an easier option :) Using the :wrap_object option of the link_to_add_association (see doc) you can prefill the user_id in the form! So something like:
= link_to_add_association ('add slide', #form_obj, :slides,
wrap_object: Proc.new {|slide| slide.user_id = current_user.id; slide })
To be completely correct, you would also have to change your new method as follows
#post.slides.build(user_id: current_user.id)
Then of course, we have to add the user_id to the form, as a hidden field, so it is sent back to the controller, and do not forget to fix your strong parameters clause to allow setting the user_id as well :)
When I'm looking at this I see three ways to go about it, but since you're on cocoon already, I would drop the connection between user & slides - as it kind of violates good database practices (until you hit a point where you page is so popular you have to optimize of course, but that would be done differently).
You are using cocoon, but you're not utilizing the nesting of the relationship fully yet ...
The best practice would be to have cocoon's nesting create both & instead of trying to assign to current_user you call something like:
#slides = current_user.posts.find_first(param[:id]).slides
The #slides saves all the results, the .Post.find(param[:id]) finds a specific post for current_user.
Note: this is not the most optimized way & I haven't tested this, but it shows you the format of one way you can think about the relationships. You will need to hit rails console and run some tests like ...
(rails console)> #user = User.first
Next we test that there are posts available, as it's frustrating to test blanks & not get the results ...
(rails console)> #posts = #user.posts
Then we use the find method & I'm going to use Post.first just to get a working id, you can easily put "1" or any number you know is valid ...
(rails console)> #post = #posts.find(Post.first)
Finally, we go with either all slides to make sure its a valid dataset
(rails console)> #post.slides
If you want a specific slide later & have a has_many relationship just tag that find method on the .slides after.
Also one last thing - when you state earlier in there you need the current_user to be related, you can use an entry in your model.rb to create a method or a scope to get the data & allow you to link it to the current_user more easily & even drop some directed SQL query with the .where method to pull that information up if performance is an issue.
I spotted a second optimization in there ... if everything really is working - don't worry about this!
And don't forget about the strong_parameters nesting to do this fully ... Strong Param white listing
Basic format ... `.permit(:id, :something, slide_attributes: [:id, :name, :whatever, :_destroy])
In my project I have 3 models Assignment, Question and MultipleChoice with the following associations
assignment.rb
has_many :questions, dependent: :destroy
question.rb
belongs_to :assignment, class_name: 'Assignment', foreign_key: :assignment_id
has_many :multiple_choices, dependent: :destroy
multiple_choice.rb
belongs_to :question
Now I want to make a query like below
#assignment = Assignment.find(params[:id])
#questions = #assignment.questions.includes(:multiple_choices)
This is not working as expected.
So, I want all questions that belongs to the assignment for the params[:id] and the associated multiple choices that belongs to a question. My above query do not give any error but it only show questions not multiple choices associated with question. How can I do this? I am learning api development for rails. So I want to send this value as json and probably I will need serialization. How can I do this? I am working on rails 4.
Edit
well the output for
#questions = #assignment.questions.includes(:multiple_choices) and
#questions = #assignment.questions.eager_load(:multiple_choices) and
#questions = #assignment.questions are all same.
I dont understand why the output do not include any value from multiple choices table
Output of the command
#assignment.questions.eager_load(:multiple_choices).to_sql id
=> "SELECT \"questions\".\"id\" AS t0_r0, \"questions\".\"content\" AS t0_r1, \"questions\".\"q_type\" AS t0_r2, \"quest
ions\".\"created_at\" AS t0_r3, \"questions\".\"updated_at\" AS t0_r4, \"questions\".\"assignment_id\" AS t0_r5, \"multi
ple_choices\".\"id\" AS t1_r0, \"multiple_choices\".\"content\" AS t1_r1, \"multiple_choices\".\"created_at\" AS t1_r2,
\"multiple_choices\".\"updated_at\" AS t1_r3, \"multiple_choices\".\"question_id\" AS t1_r4 FROM \"questions\" LEFT OUTE
R JOIN \"multiple_choices\" ON \"multiple_choices\".\"question_id\" = \"questions\".\"id\" WHERE \"questions\".\"assignm
ent_id\" = $1"
The behaviour for includes function changed in Rails 4. You can find more details here:
http://blog.arkency.com/2013/12/rails4-preloading/
I also suppose, that if you will use eager_load instead of includes, you will get the result you need.
#assignment is an object from which you are getting the questions.
But with #questions = #assignment.questions.includes(:multiple_choices) how can you get the multiple_choices without calling this on an object?
Try this->
#assignment = Assignment.includes(:questions).find(params[:id])
#assignment.questions.includes(:multiple_choices).collect {|question| question.multiple_choices }
This also includes eager loading.
Hope you'll get what you expect.
I am connecting to one of my company's SQL Server databases, and trying to set up ActiveRecord so I can treat them just the same as Rails objects.
I have these two models:
class Change < ActiveRecord::Base
belongs_to :affected_contact, class_name: "Contact"
end
class Contact
# Contact's primary key is a binary UUID; I can't change this
end
I am trying to get the affected contact of one particular change. Normally, this would be a simple case, but:
Change.first.affected_contact
Change Load (52.6ms) EXEC sp_executesql N'SELECT TOP (1) [chg].* FROM [chg] ORDER BY [chg].[id] ASC'
Contact Load (28.0ms) EXEC sp_executesql N'SELECT TOP (1) [ca_contact].* FROM [ca_contact] WHERE [ca_contact].[contact_uuid] = #0', N'#0 binary', #0 = 0xfcf9a8ac6381aa4386c9b10ee382e10b [["contact_uuid", "<16 bytes of binary data>"]]
=> nil
... that's not what I want! And yet, if I eager-load the join first, it works:
Change.eager_load(:affected_contact).first.affected_contact
SQL (34.4ms) EXEC sp_executesql N'SELECT TOP (1) holy_crap_theres_a_lot_of_columns FROM [chg] LEFT OUTER JOIN [ca_contact] ON [ca_contact].[contact_uuid] = [chg].[affected_contact] ORDER BY [chg].[id] ASC'
=> #<Contact contact_uuid: "\xFC\xF9\xA8\xACc\x81\xAAC\x86\xC9\xB1\x0E\xE3\x82\xE1\v", ... >
In fact, if I force the matching to happen in the JOIN clause in any way, it will work, but belongs_to seems to use the WHERE clause instead, and nil is the best response I can get (a lot of the time, there are conversion errors between the string and its binary type).
Is there a way to ensure eager-loading through the JOIN clause happens by default on the belongs_to association?
I found that #find_by_contact_uuid (contact_uuid being the primary key) worked, where #find didn't, for some reason. That led to this being implemented.
I have ended up essentially rewriting the association methods that Active Record supplies:
module AssociationMethods
def self.included(base)
base.reflect_on_all_associations(:belong_to).each do |a|
define_method a.name do
# #find_by_<uuid_pk> seems to work where #find doesn't
a.klass.send "find_by_#{a.association_primary_key}", self[a.foreign_key]
end
end
base.reflect_on_all_associations(:has_many).each do |a|
define_method a.name do
a.klass.where(a.foreign_key => self.send(a.association_primary_key))
end
end
end
end
class Contact
has_many :changes, foreign_key: :affected_contact_id
include AssociationMethods # include *after* all associations are defined
end
class Change
belongs_to :affected_contact, class_name: 'Contact'
include AssociationMethods
end
It doesn't cover everything that Active Record supplies when setting up the associations, but it seems to do the trick.
Using includes should resolve your problem. This is because includes will preload or eager_load depending on your other conditions.
read more here
I have following models :
class Topic < ActiveRecord::Base
has_many :topic_tags
has_many :tags, through: :topic_tags
end
class Tag < ActiveRecord::Base
STATUS_DISABLED = 0
STATUS_ENABLED = 1
has_many :topic_tags
has_many :topics, through: :topic_tags
end
I whant know how get all topics for all tags where status is STATUS_ENABLED.
I would like something like :
Topic.where(tags: {status: Tag::STATUS_ENABLED)
How the best way to do that?
EDIT:
I found fastidious solution:
Tag.includes(:topics).where(status: Tag::STATUS_ENABLED).map(&:topics).flatten
better way?
This should work:
Topic.joins(:tags).where(tags: {status: Tag::STATUS_ENABLED}).group("topics.id")
That applies an inner join. And it's much better than your tags.map(&:topics).flatten solution. The map + flatten queries the database once per enabled tag. This way it's only 1 query.
I really can't get my head around Rails 4 strong parameters, belongs_to association and form with fields_for.
Imagine I have model for quoting some price:
class Quote < ActiveRecord::Base
belongs_to :fee
accepts_nested_attributes_for :fee
Now, I have seeded some fees into the db, and have put some radiobuttons on my form_for #quote using fields_for. The values of the radiobuttons are simply ids of the records.
Here is the troubling part, the controller:
def create
#quote = Quote.new(quote_params)
...
end
def quote_params
params.require(:quote).permit(:amount_from, fee_attributes: [:id])
end
From my understanding, automagically Rails should fetch fee record with some id, but there is some mystic error instead.
params hash is: "quote"=>{"amount_from"=>"1200", "fee_attributes"=>{"id"=>"1"}}
Log tail:
Completed 404 Not Found in 264ms
ActiveRecord::RecordNotFound (Couldn't find Fee with ID=1 for Quote with ID=)
app/controllers/quotes_controller.rb:14:in `create'
I really don't understand what is going on here, have read Rails association guide, googled for hour for all info, but to no avail.
What I want to achieve here is to understand the correct "Rails way" to fetch some associations for new Quote object using some params I've put in the form.
Guess I got nested_attributes_for wrong, somehow thought it would call Fee.find automagically.
I've opted for ditching fields_for helpers from the form and rendering fields manually like
radio_button_tag 'fee[id]', fee.id
Then in controller I have 2 params methods now:
def quote_params
params.require(:quote).permit(:amount_from)
end
def fee_params
params.require(:fee).permit(:id)
end
And my action looks like
def create
#quote = Quote.new(quote_params)
#quote.fee = Fee.find(fee_params[:id])
...
Any additions on best practices when one has to handle lots of different objects with not so straight init logic are welcome.