In a Rails 3.2 app I have a User model that has many Awards.
The Award class has :type, :level and :image attributes.
On a User's show page I want to show their Awards, but with some criteria. User.awards should be grouped by both type and level, and for each type-level combination I want to display its image, and a count of the awards.
I'm struggling to construct the queries and views to achieve this (and to explain this clearly).
How can I group on two attributes of a child record, and then display both a count and attribute (i.e. image) of those children?
It took me some time to figure this out because of the complicated mix of active record objects, arrays and grouped arrays.
Anyway, incase this is useful for anyone else
Given a User has many Awards, and Award has attributes :type, :level, :image.
for award in #user.awards.group_by{ |award| [award.type,award.level] }.sort_by{|award| [award[0][0], award[0][1]]}
puts "#{(award[0][0]).capitalize} - Level #{award[0][1]}" # e.g. Award_Name - Level 1
puts award[1].first.image #outputs the value of award.image, i.e. the image url
puts award[1].count #counts the number of grouped awards
end
A bit fiddly! Maybe there are ways to optimize this code?
Depending on the database you're using you have to build a custom SQL query using a GROUP BY on type and level:
SELECT * FROM users GROUP BY users.type, users.level
(Postgres has a special interpretation of the GROUP BY so check the document of the database you're using).
To write it in Rails read the documentation: http://guides.rubyonrails.org/active_record_querying.html#group
For the count you'll have to do it in a second step (Ruby could do it using the size method on the Array of ActiveRecord object the query will return you).
Related
So, I need check three fields for uniqueness of an object before creating it (from a form), but I will create the object so long as any of the three fields are unique.
My first thought was to just pass the params from the controller to the model, and then run a query to check if a query with those three fields returns > 0 documents. However, I've since learned that this is a dangerous approach, and should not be used.
So I checked the docs, and based off of this snippet
Or even multiple scope parameters. For example, making sure that a teacher can only be on the schedule once per semester for a particular class.
class TeacherSchedule < ActiveRecord::Base
validates_uniqueness_of :teacher_id, scope: [:semester_id, :class_id]
end
I thought I had found my answer, and implemented:
validates_uniqueness_of :link_to_event, :scope => [:name_of_event, :date_of_event]
which works! But, this dataset is going to get very large (not from this form alone, lol), and I'm under the impression that with this implementation, Rails is going to query for all fields with a link_to_event, and then all fields with a name_of_event, and then all fields with a date_of_event. So, my question(s) is:
A) Am I wrong about how rails will implement this? Is it going to be more efficient out of the box?
B) If this will not be efficient for a table with a couple million entries, is there a better (and still railsy) way to do this?
You can define a method that queries the records with all the fields that you want to be unique as a group:
validate :uniqueness_of_teacher_semester_and_class
def uniqueness_of_teacher_semester_and_class
users = self.class.where(teacher_id: teacher_id, semester_id: semester_id, class_id: class_id)
errors.add :base, 'Record not unique.' if users.exists?
end
To answer your questions:
A) Am I wrong about how rails will implement this? Is it going to be more efficient out of the box?
I think Rails will query for a match on all 3 fields, and you should check the Mongo (or Rails) log to see for sure.
B) If this will not be efficient for a table with a couple million entries, is there a better (and still railsy) way to do this?
This is the Rails way. There are 2 things you can do to make it efficient:
You would need indexes on all 3 fields, or a compound index of the 3 fields. The compound index *might* be faster, but you can benchmark to find out.
You can add a new field with the 3 fields concatenated, and an index on it. But this will take up extra space and may not be faster than the compound index.
These days a couple million documents is not that much, but depends on document size and hardware.
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.
One table, one column ('headline' in an RSS feed reader). On the front end, I want a text area in which I can enter a comma-separated list of search terms, some multi-word, like for 'politics':
rajoy, pp, "popular party", "socialist party", etc
This could either be stored as part of a separate search model or as a keyword column on the 'category' or 'story' models, so they can be edited and improved with different terms from the front end, as a story develops.
In the RSS reader, have a series of links, one for each story or category, that, on being clicked return the headlines that contain one (or more) of the search terms from the stored list.
In a later version, it would be good to find headlines containing several of the terms in the list, but let's start simple.
Have been doing lots of reading about postgres, rails, different types of searches and queries, but can't seem to find what I want, which I understand is basically "search 'headlines' column against this list of search terms".
Sounds like it might be an array thing that's more to do with controllers in Rails than postgres, or cycling through a giant OR query with some multi-word terms, but I'm not sure.
Does anyone have any better pointers about how to start?
Users
If this will be user specific, I would start with a User model that is responsible for persisting each unique set of search terms. Think logon or session.
Assuming you use the Category method mentioned before, and assuming there's a column called name. Each search term would be stored as a separate instance in the database. Think tags.
headlines that contain one (or more) of the search terms from the stored list
Categories
Since each Category has many terms, and all the queries are going to be OR queries, a model that joins the User and Category, storing a search term would be appropriate.
I'm also assuming you have a Story model that contains the actual stories, although this may not be persisted in the database. I'm predicting your story model has a heading and a body.
Terminal Console
rails generage model SearchTerm query:string user:references category:references && rake db:migrate
Models
On your existing User and Category models you would add:
# app/models/user.rb
has_many :search_terms
has_many categories, through: :search_terms
# app/models/category.rb
has_many :search_terms
has_many :stories
Rails Console
This will automatically make it possible for you to do this:
#user = User.last # this is in the console, just to demonstrate
#category = Category.find_by_name("politics")
#user.search_terms.create {query: "rajoy", category: #category}
#user.search_terms.create {query: "pp", category: #category}
#user.search_terms.where(category_id: #category.id).pluck(:query)
-> ['rajoy', 'pp']
Controllers
What you will want to do with your controller (probably the Category controller) is to parse your text field and update the search terms in the database. If you want to require commas and spaces to separate fields, you could do:
#user.search_terms.where(category: #category).delete_all
params[:search_term][:query].split(", ").map{|x| x.gsub("\"", "")}.each do |term|
#user.search_terms.create({category: #category, query: term})
end
Front End
Personally though, I'd make the front end a bit less complicated to use, like either just require commas, no quotes, or just require spaces and quotes.
Search
For the grand finale, for the Stories to be displayed that have search terms in their heading:
Story.where(#user.search_terms.where(category: #category).pluck(:query).map { |term| "heading like '%#{term}%'" }.join(" OR "))
I would recommend using pg_search gem rather than trying to maintain complicated queries like this.
Note: I'm sure there are errors in this, since I wasn't able to actually create the entire app to answer your questions. I hope this helps you get started with what you actually need to do. I encourage you as you work through this to post questions that have some code.
References
Rails guides: choosing habtm or has many through
gem 'pg_search'
Stack Overflow: Search a database based on query
I have a many-to-many :through relationship going.
Users -> Memberships <- Groups
User model has a :country column.
Now I want to find out how many people of the same country are in a specific group and return only the country with the biggest amount of users.
I have this atm in by Group model;
def country
Country.find(users.group(:country_id).count.keys.first)
end
Which does not work, I saw it returns an OrderedHash, where I'm now taking the first key of, which is pointless. Just showing you were I'm lost I guess.
I want to be able to do #group.country and get the biggest country in that group.
Any help on how I would go about this?
This would be a lot easier if you used the :counter_cache feature of ActiveRecord because the numbers would be expressed in a column you could index and sort on. The alternative is to write some custom SQL to get the proper result.
The alternative is to wrangle around with a group like you have:
Country.find(users.group(:country_id).count.first.first)
Given I have a model house and it lives through several states, something like this:
Dreaming —> Planning —> Building —> Living —> Tearing down
If I would want to retrieve let's say ten houses from the databse and order them by the state field, I'd get first all houses in the Building state, then Dreaming, then Living, …
Is it possible to fetch all houses from the database and order them by the state in the order intended before retrieving them? Meaning, first all houses in the Dreaming state, then Planning, etc. E.g. by providing the order in an array for comparison of sorts.
I'd like to avoid doing this in Ruby after having fetched all entries as well as I wouldn't want to use IDs for the states.
After reading up on enum implementations, I guess, if I can make it work, I'll try to combine the enum column plugin with the state_machine plugin to achieve what I'm after. If anyone has done something like this before (especially the combination under Rails 3), I'd be grateful for input!
Here's some information on how to use SQL ENUMs in rails -- they're relatively database portable and do roughly what you want -- http://www.snowgiraffe.com/tech/311/enumeration-columns-with-rails/
If you are using MySQL, then the solution is to do ORDER BY FIELD(state, 'Building', 'Dreaming', 'Living', ...):
House.order("FIELD(state, 'Building', 'Dreaming', 'Living', ...)")
If you want to order the collection after a certain criteria then you must store that criteria somewhere.
I don't know if this goes against your "not in Ruby" criteria but I would probably do something like this:
class House < ActiveRecord::Base
STATES { 0 => "Dreaming",
1 => "Planning",
2 => "Building",
3 => "Living",
4 => "Tearing Down" }
validates_inclusion_of :state, :in => STATES.keys
def state_name
STATES[self.state]
end
end
#houses = House.order("state")
In this case the db field state is an integer instead of a string. It makes it very effective for database storage as well as querying.
Then in your view, you call state_name to get the correct name from the STATES hash stored in the model. This can also be changed to use i18n localization by using labels instead of strings in the hash.