Querying distinct with MongoMapper - ruby-on-rails-3

How do I query distinct with MongoMapper? My query is:
subscribedToThread = Comment.where(:subscribe_thread => 1).all
But this will return many objects with the same user_id. I need to return just a distinct user_id. Is this possible?

I think you will need to drop down to the ruby driver in order to do this as I don't think you can do this with MongoMapper itself:
subscribedToThread = Comment.collection.distinct("user_id", {:subscribe_thread => 1})
Calling the collection method on a model returns the collection as would be provided by the Ruby driver directly so you can issue a distinct query using the syntax below:
collection.distinct(key, query = nil)
You can read more about it here

Yes, you can do so:
subscribedToThread = Comment.where(:subscribe_thread => 1).fields(:user_id).all.compact!.unique!
This will nil every field but user_id which you then uniq!,ie you remove all doubles and then compact! all nil
http://mongomapper.com/documentation/plugins/querying.html#fields

Try this
subscribedToThread = Comment.where(:subscribe_thread => 1).fields(:user_id).collect(&:user_id).uniq
It will show you list of uniq user_id

Related

Better query using WHERE IN () when param can be nil

For example we have model TableRow - columns (:account_number, :month, :department, :phone_number). And have a method that returns filtered rows by arrays of this params.
For required params we can use
TableRow.where('account_number IN (?)', param)
Is there best way to add in this query unrequired params (department, phone_number) that can be nill and we should return records with any params in this column?
There are a couple ways to approach this. If you want your query to be static, you can check the literal value of your param with the SQL logic itself:
TableRow.where('COALESCE(:depts) IS NULL OR department IN (:depts)', depts: param)
You can also build up your relation incrementally in Ruby:
relation = TableRow.all
relation = relation.where(department: depts) if depts.present?
Your question is hard to understand, but if what you want is to filter by phone_number while still retrieving records where phone_number is null, you just have to that:
TableRow.where('phone_number IN (?)', param << nil)

using .where with .find

I am wondering how I can use where cause with the ActiveRecord find method.
Here is the code I am using:
Supplier.joins(:products).find(params[:id]).where('suppliers.permalink = ? AND variants.master = ?', params[:id], TRUE)
which gives me:
undefined method `where' for #<Supplier:0x007fe49b4eb330>
Supplier.joins(:products).find(params[:id]).where('suppliers.permalink = ? AND variants.master = ?', params[:id], TRUE)
What you're doing here is finding the first record with the id contained in params[:id], then trying to run a where statement on that single record. where only works when run against the model itself.
The confusing part here is that you are using params[:id] both for the primary key (find searches the id field) but then also comparing it to the permalink column in the where clause.
To explain the usage of both methods:
find will search for result(s) from the table, matching the argument you provide it to the id field. You can pass in multiple id's and this method is mostly used to select a row that you know exists, by id. Most commonly it is used with a single id and returns a single instance.
where is used to find all results from the table that match the clause and return a collection of records. You can then refine these results or select one, for example by using .first:
Supplier.joins(:products).where('suppliers.permalink = ? AND variants.master = ?', params[:permalink], true).first
(Note that you're using joins(:products) but then querying variants table. Is this incorrect?)
Supplier.joins(:products).where('suppliers.permalink = ? AND variants.master = ?', params[:id], TRUE).find(params[:id])

SQL injections in Rails 4 issue

I'm trying to learn about SQL injections and have tried to implement these, but when I put this code in my controller:
params[:username] = "johndoe') OR admin = 't' --"
#user_query = User.find(:first, :conditions => "username = '#{params[:username]}'")
I get the following error:
Couldn't find all Users with 'id': (first, {:conditions=>"username = 'johndoe') OR admin = 't' --'"}) (found 0 results, but was looking for 2)
I have created a User Model with the username "johndoe", but I am still getting no proper response. BTW I am using Rails 4.
You're using an ancient Rails syntax. Don't use
find(:first, :condition => <condition>) ...
Instead use
User.where(<condtion>).first
find accepts a list of IDs to lookup records for. You're giving it an ID of :first and an ID of condition: ..., which aren't going to match any records.
User.where(attr1: value, attr2: value2)
or for single items
User.find_by(attr1: value, attr2: value)
Bear in mind that while doing all this, it would be valuable to check what the actual sql statement is by adding "to_sql" to the end of the query method (From what I remember, find_by just does a LIMIT by 1)

SQL select distinct value

I'm trying to select the following data with the limited information. The problem is that when I have added the .select distinct section it has killed my query.
#activities = Availability.select.("DISTINCT user_id").where("team_id = ? and schedule_id = ?", current_user[:team_id], #next_game).last(5)
There's one too many dot's in there as the 'DISTINCT user_id' is the arguments for the select method call.
So:
Availability.select("DISTINCT user_id").where("team_id = ? and schedule_id = ?", current_user[:team_id], #next_game).last(5)
Also be aware that you're now only selecting one attribute and you'll get a partial representation of the classes back. To circumvent this just select the attributes you need later in the code.
Availability.select("DISTINCT(`user_id`), `team_id`").where("team_id = ? and schedule_id = ?", current_user[:team_id], #next_game).last(5)
etc.
Hope this helps.

get only one row and one column from table using nhibernate

I have query:
var query = this.session.QueryOver<Products>()
.Where(uic => uic.PageNumber == nextPage[0])
.SingleOrDefault(uic => uic.ProductNumber)
But this query result is type Products. It is possible that result will be only integer type of column ProductNumber ?
Try something like this:
var query = this.session.QueryOver<Products>()
.Where(uic => uic.PageNumber == nextPage[0])
.Select(uic => uic.ProductNumber)
.SingleOrDefault<int>();
Since you need a single primitive type value, you can do .Select to define the result column, and then do .SingleOrDefault to get the only result. For complex types, you'd need to use transformers.
You can find more info about QueryOver in this blog post on nhibernate.info: http://nhibernate.info/blog/2009/12/17/queryover-in-nh-3-0.html
You can use Miroslav's answer for QueryOver, but this would look cleaner with LINQ:
var productNumber = session.Query<Products>()
.Where(uic => uic.PageNumber == nextPage[0])
.Select(uic => uic.ProductNumber)
.SingleOrDefault();
Notice you don't need a cast, as the Select operator changes the expression type to the return type of its parameter (which is the type of ProductNumber).