I have 3 tables:
table 1 has column price
tabel 2 has column total
table 3 has column total_price
Question:
I want the column total_price is the result from multiplication of
price and total:
total_price = price * total
im very newbie.
Do it like this:
Table1.all.each_with_index do |el, index|
Table3.create(total_price: el.price * Table2.all[index])
end
I am not going into all the details like relations, but the comments below make the point, but let's assume that these tables might have been just an extraction from Excel table or something like that.
Of course this is only if you want to create the third table. I am assuming that is what you want (?)
Related
I have a table called vehicles, which has a column called vehicle_id and price.
I have a table called sales, which references the vehicles table. It has the columns vehicle_id (references the vehicle table) and sale_status which can equal to 'sold' or 'loan'.
I am trying to calculate the total price of vehicles which equal to 'sold' in the sales table. Help is much appreciated!
This is what I have so far but it returns the wrong number.
vehicle.rb:
def self.vehicles_price_sum
vehicles_sold.sum(:price).to_f
end
def self.vehicles_sold
Vehicle.where(id: Sale.where(sale_status: 'Sold'))
end
You can try with a subquery (which is close to you solution, yet you need to provide a column name explicitly for in clause with select, otherwise sales' id column is going to be provided):
Vehicle.where(id: Sale.where(status: "Sold").select(:vehicle_id)).sum(:price)
# SELECT SUM(`vehicles`.`price`) FROM `vehicles` WHERE `vehicles`.`id` IN (SELECT `sales`.`vehicle_id` FROM `sales` WHERE `sales`.`sale_status` = 'Sold')
I have a table user_keywords which :belongs_to :keywords. user_keywords has a column keyword_id, user_id, and relevance_score (float).
keyword table has a column 'name'.
I want to group all the user_keywords by their keyword_id.
I want to take the average of each of those groups' relevance_score
I want to sort groups by the highest relevance score
I want to return the name of the keyword from the groups, sorted by highest relevance score.
What is the most efficient way to query this?
try this:
Keyword.joins(:user_keywords)
.select('keywords.name, avg(user_keywords.relevance_score) as score')
.group('keywords.name')
.order('score DESC')
.map(&:name)
Say I have an ActiveRecord object that contains a quantity and a price stored in the database.
I have defined a accessor for the total_price:
def total_price
quantity * price
end
Now what if I want to use this dynamic "attribute" in multiple ActiveRecord query contexts? I might to sum on it, compute average, for multiple scope, etc.
What would be the best practices so that I don't have to repeat this quantity * price with ActiveRecord and if I don't want to denormalize by writing it in DB?
Thanks!
Well we wanted to get caption (from join model) to appear on our associated image model (I.E if you called #user.images, you'd be able to call image.caption (even though caption was in the join model)
So we looked at this RailsCast (you'll benefit from around 6:40) which gave us some information about how you can use join to create more dynamic queries. We ended up using this:
has_many :images, -> { select("#{Image.table_name}.*, #{ImageMessage.table_name}.caption AS caption") }
I'm thinking you could use something similar for your request (include some SQL to create the pseudo column in the object). Since it's the origin model, I'm thinking about a scope like this:
default_scope select("(table.quantity * table.price) as total_price")
I assume price is stored in the database. Is quantity stored in the database? If both are stored, why not make total_price a database column as well? You can update total_price whenever you update the record.'
class Order < AR::Base
before_update :update_total_price
def update_total_price
self[:total_price] = quantity * price
end
end
Obviously you can do anything you would with an ordinary column, like Order.where("total_price > 1.0") and what-not.
In Rails 3, how do i select rows based on unique column values, i need to get all the columns for eg:
SELECT COUNT(DISTINCT date) FROM records
This only returns date column, but i want all the columns (name, date , age , created_at) columns not just the date.
Thanks for your help
The issue here is that, by definition, there may be multiple records with the same date. It requires logic in the user space to determine which of the multiple records with the unique date to use. Here's some code to get those rows:
Record.select("distinct date").each do |record|
records = Record.find_by_date record.date
puts records.count # do something with the records
end
If what you're really after is uniqueness among multiple columns, list all the relevant columns in the distinct query:
Record.select("distinct date, name, age, created_at").each do |record|
puts record.date
puts record.name
puts record.age
puts record.created_at
# ``record'' still represents multiple possible records
end
The fact that you are using distinct means that each "row" returned actually represents n rows, so the DB doesn't know which of the n rows to pull the remaining columns from. That's why it only returns the columns used in distinct. It can do no other...
I think this will help you
Model.find(:all, :select => 'DISTINCT name, date, age, created_at')
Please use it and let me know.
Model.group(:column)
For your case:
Record.group(:date)
This will return all your columns with no "date" repetitions.
For rails 3.2 and higher, Model.select('DISTINCT name, date, age, created_at')
I am building grade-book report - a two dimensional table that shows lesson names going horizontally and a list of students going vertically.
Student Name | LessonID x | LessonID x | LessonID x
Joe 95% 95%
Mary 80% 80%
Sam 80% 80%
My data is in a table that has these fields:
student_id, lesson_id, grade_in_pct, grade_in_pts, grade_high, grade_low, grade_median
The total number of students and lessons is not fixed.
I considered using ruport/acts_as_reportable or mysql pivot procedure, however it looks like the pivot only gives me one dimension. So that's not going to work, because in my view I want to add mouse-over features and conditional formatting to show more info on each grade.
So I think my only option is to generate a nested hash and then loop through it in the view. What are your thoughts? Could someone suggest a way to build a nested hash? Would it be too processor intensive to loop through 250 rows (~50 students, 5 lessons each)?
I am stuck. Please help. Thanks!
This is how I would do it:
MODELS:
Student Model:
has_many: Grades
has_and_belongs_to_many: Lessons
Lesson Model:
has_many: Grades
has_and_belongs_to_many: Students
Grade Model:
belongs_to: Student, Lesson
CONTROLLER:
#data = Student.all
#lessons = Lesson.all
VIEW:
header_row
#data.each do |student|
#lessons.each do |lesson|
student.grades.find_by_lesson(lesson).some_data