I need to store a pricelist in the database.
What is the best way to store a pricelist?
Example of the pricelist:
I have thinked of 2 solutions.
Create a table named products, with the columns:
name (varchar)
price (integer)
price_2 (integer)
The name would then be example for example be "product_a1" used to refer to the YAML translation file.
And then create all the name of the products. So example in my case there would be about 100.
Solution 2:
Store all the data in one row. So the table columns would be:
product_a1
product_a2
product_a3
product_b1
product_b1_2
product_b2
product_b2_2
and 99 more..
PS: I have only 1 pricelist
Why don't you use the Entity–attribute–value model (EAV), this way you can get as many attributes on your model as you want. It gives you great flexibility, so in the future you can add more attributes dynamically without refactoring your code.
Why not create two tables with a relationship between them:
class Product < ActiveRecord::Base
has_many :prices
end
and
class Price < ActiveRecord::Base
belongs_to: :product
end
This gives you the flexibility to add additional prices in the future if necessary. I'm loath to hardcode databases with fixed limits.
Related
I've got a Match model and a Team model.
I want to count how many goals a Team scores during the league (so I have to sum all the scores of that team, in both home_matches and away_matches).
How can I do that? What columns should I put into the matches and teams database tables?
I'd assume your Match model looks something like this:
belongs_to :home_team, class_name:"Team"
belongs_to :away_team, class_name:"Team"
attr_accessible :home_goal_count, :away_goal_count
If so, you could add a method to extract the number of goals:
def goal_count
home_matches.sum(:home_goal_count) + away_matches.sum(:away_goal_count)
end
Since this could be expensive (especially if you do it often), you might just cache this value into the team model and use an after_save hook on the Match model (and, if matches ever get deleted, then an after_destroy hook as well):
after_save :update_team_goals
def update_team_goals
home_team.update_attribute(:goal_count_cache, home_team.goal_count)
away_team.update_attribute(:goal_count_cache, away_team.goal_count)
end
Since you want to do this for leagues, you probably want to add a belongs_to :league on the Match model, a league parameter to the goal_count method (and its query), and a goal_count_cache_league column if you want to cache the value (only cache the most recently changed with my suggested implementation, but tweak as needed).
You dont put that in any table. Theres a rule for databases: Dont ever store data in your database that could be calculated from other fields.
You can calcuate that easyly using this function:
def total_goals
self.home_matches.collect(&:home_goals).inject(&:+)+self.away_matches.collect(&:away_goals).inject(&:+)
end
that should do it for you. If you want the mathes filtered for a league you can use a scope for that.
Kind of new to Ruby/Rails, coming from c/c++, so I'm doing my baby steps.
I'm trying to find the most elegant solution to the following problem.
Table A, among others has a foreign key to table B (let's call it b_id), and table B contains a name field and a primary (id).
I wish to get a list of object from A, based on some criteria, use this list's b_id to access Table B, and retrieve the names (name field).
I've been trying many things which fail. I guess I'm missing something fundamental here.
I tried:
curr_users = A.Where(condition)
curr_names = B.where(id: curr_users.b_id) # fails
Also tried:
curr_names = B.where(id: curr_users.all().b_id) # fails, doesn't recognize b_id
The following works, but it only handles a single user...
curr_names = B.where(id: curr_users.first().b_id) # ok
I can iterate the curr_users and build an array of foreign keys and use them to access B, but it seems there must be more elegant way to do this.
What do I miss here?
Cheers.
Assuming you have following models:
class Employee
belongs_to :department
end
class Department
has_many :employees
end
Now you can departments based on some employee filter
# departments with employees from California
Department.include(:employees).where(:employees => {:state => "CA"}).pluck(:name)
For simplicity, let's take an example of Article and Comments, instead of A and B.
A Comment has a foreign key article_id pointing at Article, so we can setup a has_many relationship from Article to Comment and a belongs_to relationship from Comment to Article like so:
class Article < ActiveRecord::Base
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :article
end
Once you have that, you will be able do <article>.comments and Rails will spit out an array of all comments that have that article's foreign key. No need to use conditionals unless you are trying to set up a more complicated query (like all comments that were created before a certain date, for example).
To get all the comment titles (names in your example), you can do <article>.comments.map(&:title).
I'm trying to set up a proper database-design, but I'm stuck.
Here is what I'm trying to save.
Every user can define a vote history list from imdb looking like this.
Two users can define the same list.
First I want to be able to save each list as an imdb_vote_history_list - list.
class ImdbVoteHistoryList < ActiveRecord::Base
has_and_belongs_to_many :vote_history_list
has_and_belongs_to_many :movies
# Fields
# id (Integer) - defined by the user
end
Each list should be unique and is being defined by it's ID (given in the link).
Each list has and belongs to many movies, as in the code above.
Each user should be able to pick a name for every list.
So instead of saying
Each imdb_vote_history_list belongs_to user
I create a new relation called vote_history_list.
class VoteHistoryList < ActiveRecord::Base
has_and_belongs_to_many :imdb_vote_history_lists
belongs_to :user
# Fields
# name (String)
end
Here the user can pick any name for the list, without interference with other user's names.
Is this a good way to store the data?
From the theoretical database design view this is the right approach.
For example the entity relationship model describes it this way. You can have relationships between entities and attributes at those relationships. If you map those to a relational model (database tables) you get a table for the relationship containing references to both entites and all additional information.
This is what theory can tell us about it :)
I have situation where a single model needs to have three foreign ids. This table has the information which belongs to three models.
e.g. -
Three models - Keyboard, Mouse, Monitor
Now i have fourth model details - which has information about what will happen for any combination like keyboard1, mouse1 and monitor1.
So what should be good design pattern for this ?
Right now what i use is Detail.find_by_keyboard_id_and_mouse_id_and_monitor_id(keyboard1id, mouse1id, monitor1id) #=> Detail1
Which of course is not a best way to go...
I don't think what you have is a bad design. There probably aren't too many options for how this should be implemented, but you should think about how you want to use it. Personally, I wouldn't call the model Detail since it doesn't tell you anything about what the model really is. Something like HardwareConfiguration is more explicit. Maybe too lengthy, but you could shorten it to HardwareConfig or Configuration, depending on your taste.
This model should have an id and the three foreign keys. You should add database indexes to each foreign key field as well.
class Detail < ActiveRecord::Base
belongs_to :keyboard
belongs_to :mouse
belongs_to :monitor
end
Then each hardware model would have_many :details like:
class Keyboard < ActiveRecord::Base
has_many :details
end
You could look up the detail combo by its ID, or any combination of foreign keys.
Detail.find(id)
Detail.find_all_by_keyboard_id(keyboard_id)
I have a rails app with some nested data that I'd like to export as a CSV file
The models look like:
class ContainerRecord < ActiveRecord::Base
has_many :child_records
and
class ChildRecord < ActiveRecord::Base
belongs_to :container_record
I'd like to be able to export a CSV file with each ContainerRecord on a row with its information in the first few columns and a value from each ChildRecord in the remaining columns.
I can't guarantee the number of ChildRecords associated with each ContainerRecord and I don't care if I have a different number of non-null columns for each row.
I've attempted to use FasterCSV, but I get all of the data for the child records shoved into one column rather than a column for each.
Is this something that I can do with FasterCSV? If not, what method can I use to accomplish my goal?
Not sure about FasterCSV but a quick & dirty solution could be:
class ParentClass < AR::Base
has_many :children
def self.csv
all.map do |object|
( object.attributes.values + object.children.map(&:child_field) ).flatten.join(',')
end.join("\n")
end
end
Replacing "child_field" with the field you want to take from your child model of course.
I ended up finding a nice tutorial on csv_builder that let me do exactly what I wanted to do with minimal effort and allowed me to stick a little more closely to the MVC architecture.