Working on a learning management system. NOT a RoR person. Have the line of HAML to generate an average score based on quizzes taken:
="#{(QuizResult.average('score', :conditions => "user_id = #{#user.id}") * 100).round}%"
The quiz_results table has columns for used_id and score.
However, if there are no records in the quiz_results table, the page doesn't render. I want to check if any scores exist for that user id, and if so, to show the average. If none exist, I want to display "No quizzes taken." here's what I have:
19: %td
20: -if QuizResult('score', :conditions => "user_id = #{#user.id}").exists?
21: ="#{(QuizResult.average('score', :conditions => "user_id = #{#user.id}") * 100).round}%"
22: -else
23: %em No quizzes taken
I get the following error:
"ActionView::TemplateError (undefined method `QuizResult' for #ActionView::Base:0x7028c7f5cb88>) on line #20 of app/views/manage_users/show_all_users.haml:"
I've been struggling all day with this. Any suggestions? Thanks in advance, from an RoR noob.
I am guessing that QuizResult is a model class. If that is the case then you cannot use it as a method to look up an instance.
There are various ways that you can look up an object by some condition, for example:
- if QuizResult.find_by_user_id(#user_id).present?
To check for null (or nil as its referred to in Ruby) you can use the nil? method that Ruby itself provides or the Rails convenience method present? which returns true unless the object is nil, an empty string or empty collection.
You might check your quotes. For the condiitions hash, it looks like you should be using single quotes rather than doubles.
Related
I have a User model that has all the queried fields with the existing data in the database. When I execute the following query-
#user = User.find(4, :select => 'user_fname, user_lname')
Rails throws the following error for the above line
Couldn't find all Users with 'user_id': (4, {:select=>"user_fname, user_lname"}) (found 1 results, but was looking for 2)
What's going wrong?
You can try this. I hope this will help.
#user = User.where("id = ?", 4).select( "user_fname, user_lname")
Rails 4 : use pluck as a shortcut to select one or more attributes without loading a bunch of records just to grab the attributes you want.
Try:
> User.where(id: 4).pluck(:user_fname , :user_lname).first
#=> ["John", "Smith"] # this is just sample of output
You are using #find incorrectly. It takes IDs as arguments, not SQL. It's trying to use that second argument as an ID, which clearly won't work.
http://api.rubyonrails.org/classes/ActiveRecord/FinderMethods.html#method-i-find
find only finds records by id. You can pass in an array of id's but it doesn't take any options. So it thinks the hash you are passing is an id, and it bombs because it can't find a record with that ID. I think what you want is something like:
#user = User.find(4)
fname = #user.fname
lname = #user.lname
I have a mysql query that returns this type of data:
{"id"=>1, "serviceCode"=>"1D00", "price"=>9.19}
{"id"=>2, "serviceCode"=>"1D01", "price"=>9.65}
I need to return the id field based on a match of the serviceCode.
i.e. I need a method like this
def findID(serviceCode)
find the row that has the service code and return the ID
end
I was thinking of having a serviceCodes.each do |row| method and loop through and essentially go
if row == serviceCode
return row['id']
end
is there a faster / easier way?
You can use the method Enumerable#find:
service_codes = [
{"id"=>1, "serviceCode"=>"1D00", "price"=>9.19},
{"id"=>2, "serviceCode"=>"1D01", "price"=>9.65}
]
service_codes.find { |row| row['serviceCode'] == '1D00' }
# => {"id"=>1, "serviceCode"=>"1D00", "price"=>9.19}
If you use Rails Active Record as ORM and your Model named Product (only for example),
you can use something like this:
def findID(serviceCode)
Product.select(:id).where(serviceCode: serviceCode).first
end
If you have plain SQL Query in plain ruby class (not recommended), you should change this query to get only the id, as Luiggi mentioned. But aware of SQL Injections if your serviceCode coming from external Requests.
I'm writing a Sinatra application with Sequel. For the first time, I'm trying to add a currency. After looking on-line I used Numeric as a value, of course goes without saying that I need a precision of decimal points.
I know that in MySQL, Numeric and Decimal is the same. So I wonder what I'm doing wrong here. I have the feeling that I need to define the decimal points somehow. Here my model:
# Contracts table: Here the users can define their contracs
DB.create_table?(:contracts, engine: 'InnoDB') do
primary_key :id
Integer :user_id, null: false
String :name, null: false
String :description
Numeric :cost, null: false
end
Every time I try to submit a value with decimal points I get the following error, which I think it's a validation error. I don't use validations explicitly yet, so I think it's either Sequel or MySQL specific.
How should I change my models in order to allow me to add decimal values?
EDIT: As requested I add my controller (routes) file:
class Metro < Sinatra::Base
get "/user_add_contract" do
protected!
haml :user_add_contract
end
post "/user_add_contract" do
protected!
user = session['name']
begin
uid = User.first(username: user)
Contract.create(user_id: uid[:id], name: params['name'], description: params['description'], cost: params['cost'].to_f)
redirect '/user_list_contract'
rescue Exception => e
#error = e
haml :details_error
end
end
end
and the HAML (views):
%form(action="/user_add_contract" method="post")
%fieldset
%legend Φόρμα Νέου Συμβολαίου
%div{class: 'column1of2'}
%ul
%li
%label(for="name")Ονομασία:
%input#name(name="text" name="name")
%li
%label(for="description")Περιγραφή:
%textarea.email#description(type="text" name="description")
%li
%label(foor="cost")Κόστος:
%input#cost(type="number" name="cost")
%li
%input(type="submit" value="Εγγραφη") ή Ακύρωση
thanks
Related answer: How to handle floats and decimal separators with html5 input type number
The step="" attribute defaults to 1 here, meaning that it will truncate everything after the decimal point (or kick back an error, depending on how it's set up and what browser you're using).
Try setting step="0.01", on the input element, assuming that you just want to get to the nearest cent, and see if that works. Everything else in your code looks fine.*
Except that you have "foor" instead of "for" in your cost <label>
So I use the PDO for a DB connection like this:
$this->dsn[$key] = array('mysql:host=' . $creds['SRVR'] . ';dbname=' . $db, $creds['USER'], $creds['PWD']);
$this->db[$key] = new PDO($this->dsn[$key]);
Using PDO I can then execute a MySQL SELECT using something like this:
$sql = "SELECT * FROM table WHERE id = ?";
$st = $db->prepare($sql);
$st->execute($id);
$result = $st->fetchAll();
The $result variable will then return an array of arrays where each row is given a incremental key - the first row having the array key 0. And then that data will have an array the DB data like this:
$result (array(2)
[0]=>[0=>1, "id"=>1, 1=>"stuff", "field1"=>"stuff", 2=>"more stuff", "field2"=>"more stuff" ...],
[1]=>[0=>2, "id"=>2, 1=>"yet more stuff", "field1"=>"yet more stuff", 2=>"even more stuff", "field2"=>"even more stuff"]);
In this example the DB table's field names would be id, field1 and field2. And the result allows you to spin through the array of data rows and then access the data using either a index (0, 1, 2) or the field name ("id", "field1", "field2"). Most of the time I prefer to access the data via the field names but access via both means is useful.
So I'm learning the ruby-mysql gem right now and I can retrieve the data from the DB. However, I cannot get the field names. I could probably extract it from the SQL statement given but that requires a fair bit of coding for error trapping and only works so long as I'm not using SELECT * FROM ... as my SELECT statement.
So I'm using a table full of State names and their abbreviations for my testing. When I use "SELECT State, Abbr FROM states" with the following code
st = #db.prepare(sql)
if empty(where)
st.execute()
else
st.execute(where)
end
rows = []
while row = st.fetch do
rows << row
end
st.close
return rows
I get a result like this:
[["Alabama", "AL"], ["Alaska", "AK"], ...]
And I'm wanting a result like this:
[[0=>"Alabama", "State"=>"Alabama", 1=>"AL", "Abbr"=>"AL"], ...]
I'm guessing I don't have the way inspect would display it quite right but I'm hoping you get the idea by now.
Anyway to do this? I've seen some reference to doing this type of thing but it appears to require the DBI module. I guess that isn't the end of the world but is that the only way? Or can I do it with ruby-mysql alone?
I've been digging into all the methods I can find without success. Hopefully you guys can help.
Thanks
Gabe
You can do this yourself without too much effort:
expanded_rows = rows.map do |r|
{ 0 => r[0], 'State' => r[0], 1 => r[1], 'Abbr' => r[1] }
end
Or a more general approach that you could wrap up in a method:
columns = ['State', 'Abbr']
expanded_rows = rows.map do |r|
0.upto(names.length - 1).each_with_object({}) do |i, h|
h[names[i]] = h[i] = r[i]
end
end
So you could collect up the rows as you are now and then pump that array of arrays through something like what's above and you should get the sort of data structure you're looking for out the other side.
There are other methods on the row you get from st.fetch as well:
http://rubydoc.info/gems/mysql/2.8.1/Mysql/Result
But you'll have to experiment a little to see what exactly they return as the documentation is, um, a little thin.
You should be able to get the column names out of row or st:
http://rubydoc.info/gems/mysql/2.8.1/Mysql/Stmt
but again, you'll have to experiment to figure out the API. Sorry, I don't have anything set up to play around with the MySQL API that you're using so I can't be more specific.
I realize that php programmers are all cowboys who think using a db layer is cheating, but you should really consider activerecord.
I don't know if I'm just looking in the wrong places here or what, but does active record have a method for retrieving a random object?
Something like?
#user = User.random
Or... well since that method doesn't exist is there some amazing "Rails Way" of doing this, I always seem to be to verbose. I'm using mysql as well.
Most of the examples I've seen that do this end up counting the rows in the table, then generating a random number to choose one. This is because alternatives such as RAND() are inefficient in that they actually get every row and assign them a random number, or so I've read (and are database specific I think).
You can add a method like the one I found here.
module ActiveRecord
class Base
def self.random
if (c = count) != 0
find(:first, :offset =>rand(c))
end
end
end
end
This will make it so any Model you use has a method called random which works in the way I described above: generates a random number within the count of the rows in the table, then fetches the row associated with that random number. So basically, you're only doing one fetch which is what you probably prefer :)
You can also take a look at this rails plugin.
We found that offsets ran very slowly on MySql for a large table. Instead of using offset like:
model.find(:first, :offset =>rand(c))
...we found the following technique ran more than 10x faster (fixed off by 1):
max_id = Model.maximum("id")
min_id = Model.minimum("id")
id_range = max_id - min_id + 1
random_id = min_id + rand(id_range).to_i
Model.find(:first, :conditions => "id >= #{random_id}", :limit => 1, :order => "id")
Try using Array's sample method:
#user = User.all.sample(1)
In Rails 4 I would extend ActiveRecord::Relation:
class ActiveRecord::Relation
def random
offset(rand(count))
end
end
This way you can use scopes:
SomeModel.all.random.first # Return one random record
SomeModel.some_scope.another_scope.random.first
I'd use a named scope. Just throw this into your User model.
named_scope :random, :order=>'RAND()', :limit=>1
The random function isn't the same in each database though. SQLite and others use RANDOM() but you'll need to use RAND() for MySQL.
If you'd like to be able to grab more than one random row you can try this.
named_scope :random, lambda { |*args| { :order=>'RAND()', :limit=>args[0] || 1 } }
If you call User.random it will default to 1 but you can also call User.random(3) if you want more than one.
If you would need a random record but only within certain criteria you could use "random_where" from this code:
module ActiveRecord
class Base
def self.random
if (c = count) != 0
find(:first, :offset =>rand(c))
end
end
def self.random_where(*params)
if (c = where(*params).count) != 0
where(*params).find(:first, :offset =>rand(c))
end
end
end
end
For e.g :
#user = User.random_where("active = 1")
This function is very useful for displaying random products based on some additional criteria
Strongly Recommend this gem for random records, which is specially designed for table with lots of data rows:
https://github.com/haopingfan/quick_random_records
Simple Usage:
#user = User.random_records(1).take
All other answers perform badly with large database, except this gem:
quick_random_records only cost 4.6ms totally.
the accepted answer User.order('RAND()').limit(10) cost 733.0ms.
the offset approach cost 245.4ms totally.
the User.all.sample(10) approach cost 573.4ms.
Note: My table only has 120,000 users. The more records you have, the more enormous the difference of performance will be.
UPDATE:
Perform on table with 550,000 rows
Model.where(id: Model.pluck(:id).sample(10)) cost 1384.0ms
gem: quick_random_records only cost 6.4ms totally
Here is the best solution for getting random records from database.
RoR provide everything in ease of use.
For getting random records from DB use sample, below is the description for that with example.
Backport of Array#sample based on Marc-Andre Lafortune’s github.com/marcandre/backports/ Returns a random element or n random elements from the array. If the array is empty and n is nil, returns nil. If n is passed and its value is less than 0, it raises an ArgumentError exception. If the value of n is equal or greater than 0 it returns [].
[1,2,3,4,5,6].sample # => 4
[1,2,3,4,5,6].sample(3) # => [2, 4, 5]
[1,2,3,4,5,6].sample(-3) # => ArgumentError: negative array size
[].sample # => nil
[].sample(3) # => []
You can use condition with as per your requirement like below example.
User.where(active: true).sample(5)
it will return randomly 5 active user's from User table
For more help please visit : http://apidock.com/rails/Array/sample