I have a model Score and a model Adjustment. A Score has many Adjustments.
I also have a list of scores with adjustements that I wish to be able to update without affecting the db. I want to be able to do something like this:
scores.each do |score|
score.adjustments << some_new_adjustment
score.adjustments.delete_all(some_old_adjustments)
end
In the end, the scores array should change, but no query to the db should have been executed. How can I achieve this?
The guide shows no method to do that https://guides.rubyonrails.org/association_basics.html#has-many-association-reference
But you should be able to get the associated elements as an array, remove the one you don't want and then assign the new array. It shouldn't change the database until you save the parent.
current = score.ajustments.to_a
new_adjustments = current + new_adjustment - old_adjustment
score.adjustments = new_adjustments
Related
I have a table called group. I want this method to return just the content of the relevant record's ID field. At the moment it returns an active record object ID.
def get_group_name(group_id)
Group.select([:name]).where("id = ?", group_id)
end
Thanks in advance.
I think you can do easier with find
def get_group_name(group_id)
Group.find(group_id).name
end
This will get you only the name of the group.
def get_group_name(group_id)
Group.where(id: group_id).limit(1).pluck(:name).first
end
It will run this query:
SELECT name
FROM groups
WHERE id = ?
LIMIT 1;
A side note is, be careful of what you’re doing. Any time you have a method to get a single field’s value, while it can be more efficient at times, it can easily be misused. If you’re looping over a collection of group ids trying to grab all of the names, then you’d be better off 1 query up front for all of the names as opposed to 1 per group id on the page. So just keep and eye on your console and pay attention to the queries you’re running.
Also, if you are looking over a collection, you may want to look into includes for your ActiveRecord queries, to include the group data in the previous query. You can benchmark this all to figure out what’s fastest for your use case.
I have a custom model called product, and it has many reviews.
i have a method that calculates the review
def rating
total = 0
reviews_count = reviews.count
return 0 if reviews_count == 0
reviews.each do |review|
total += review.grade
end
total.to_f/reviews_count
end
i would like to know how could i use this method to Order my products.
At products_controller.rb, if i use:
#products = Product.all.order("price")
its easy, it gives me the products list ordered by price. But, if i use, for example:
#products = Product.all.sort_by{|p| p.rating}
it gives me an array and not a "ActiveRecord::Relation"
I would like to know how could i order my product using a custom method that returns a value.
In general, you can't. Ordering happens in your database, which has no knowledge about any method you typed in your application. What you need is a way of translating your method into a valid sql. In your case, you can do:
Product.joins(:reviews).group('products.id').order('AVG(reviews.grade)')
That will give you sorted results and the relation object. However, relations with join are not that nice to work with, especially if you try to add another join. Also this might get quite slow when your database grows.
What you're doing in your example is running the query then using sort_by to sort the result set.
If you want to get back an activerecord collection instead of an array, and potentially chain this with other scopes, you should move the logic from your method into SQL, and put it in a scope.
How do I get records from a table with a specific ID and store these records in an Array?
For better understanding I try to explain it to you more clear:
Imagine a table with the following columns: (ID,FIX_ID,AMOUNT)
where ID is an unique ID which always will auto_incremented by 1.
FIX_ID is an ID which can appear multiple times in the table.
And AMOUNT is just a simple type which represents the amount of some "things".
So all I want to get now is every record from the table which have the FIX_ID that I am looking for.
Remember: The FIX_ID is not unique => it can appear multiple times.
And that's it. So imagine that I want to get all records with the FIX_ID of 10. All these records which I will get should be stored in an Array.
My question to you: Is it possible to realize this "request" to the database with ActiveRecord?
If so, then how?
You can get an ActiveRecord::Relation object like this:
ModelName.where('FIX_ID = ?', 10)
Relation object will perform a database query as soon as you call methods like all, each or any? on it. If you really need an array, call to_a on that Relation:
ModelName.where('FIX_ID = ?', 10).to_a
I am loading data from two models, and once the data are loaded in the variables, then I need to remove those items from the first relation, that are not in the second one.
A sample:
users = User.all
articles = Articles.order('created_at DESC').limit(100)
I have these two variables filled with relational data. Now I would need to remove from articles all items, where user_id value is not included in the users object. So in the articles would stay only items with user_id, that is in the variable users.
I tried it with a loop, but it was very slow. How do I do it effectively?
EDIT:
I know there's a way to avoid doing this by building a better query, but in my case, I cannot do that (although I agree that in the example above it's possible to do that). That thing is that I have in 2 variables loaded data from database and I would need to process them with Ruby. Is there a command for doing that?
Thank you
Assuming you have a belongs_to relation on the Article model:
articles.where.not(users: users)
This would give you at most 100, but probably less. If you want to return 100 with the condition (I haven't tested, but the idea is the same, put the conditions for users in the where statement):
Articles.includes(:users).where.not(users: true).order('created_at DESC').limit(100)
The best way to do this would probably be with a SQL join. Would this work?
Articles.joins(:user).order('created_at DESC').limit(100)
I have a class Question which has a lot of assocated models. On one page on my app i list a summary of all the current questions, with various info from associated records. Ultimately this is a hash of values that i then just print out into a csv-style row (i'll call this the 'row hash' from hereon)
I now have a requirement to only show the changes to questions (or their associated data) over a given period. I'm currently deliberating the best way to do this. Here's some ideas i've had so far, i'd welcome any feedback, thoughts, suggestions etc.
1) Approach 1 - acts_as_audited
This was my first thought as i've used this before in other apps. The porblem with aaa though is that it only tracks changes to the record's data (ie it doesn't care if the associations change). So, i could audit all of the associated records as well but then trying to piece together what had changed by tying different audit records together sounds like a nightmare.
2) Save the old and new hash out into serialized fields: ie
- when someone goes to the question/edit page, i calculate the current row hash and save it in a serialized field "old_data" in the question table. Then after they save the question i calculate the new current row hash and save it into a serialized field "new_data" in the question table. Also, i compare the two serialized hashes and save the differences into another serialized hash field 'changes'. Now to do my report i just look for questions updated in the last x days and output their changes data.
3) make a view
- i make a view which corresponds to the data that i want to output (ie that amalgamates all the data that i pull into my report). Then i track changes to the view - somehow. I'm not sure how exactly i would do that.
I'm leaning towards option 2 right now.
Any other thoughts/comments? grateful for any suggestions - max.
So, like you said, you only want to show changes to the records between time x and time y, right? This would seem perfect to me using the acts_as_audited plugin because you end up with a table of changes, right? So make a has_many_through association from Question to all these related tables, then search it for related changes, where date created is after time X. This would return a list of changes. From there, you could connect this list back to the parent object if you need to, or whatever - but it in the end seems like a more reasonable thing to search. You're not looking for a list of related objects, after all, you're looking for a list of changes, so having a table of changes seems a reasonable way to accomplish that?
Hey I had a similar problem, check this out. If you can, go with Mongoid or Mongomapper, embedded versioned documents are sweet.
Thanks guys. I ended up rolling my own solution because what i really needed to do was to capture changes in the results of various methods called on the object, some of which involved associated objects. I wasn't so much interested in the associated objects as (for example) a text string generated as a result of looking at a few different associated objects. I had methods to do all of this already so i really just needed to track changes in the results of calling these methods.
None of the plugins i saw could really do that simply and effectively, so i ended making a table called states which just holds a serialized hash with results of all of these method calls. This gets saved when the record is altered and saved or when any of the relevant associated objects get altered and saved. Then i have some methods to return the differences between different saved state records. It works well for my needs. Thanks very much for your advice anyway.