I have a collection of DTO's in which I want to do some ordering by the sum of some values in a nested DTO.
The hiearchy is as follows:
Its a collction of QuestionDTO's.
A QuestionDTO has Many Answers which has Many Votes.
So in short:
1 QuestionDto: QuestionID, QuestionTitle, ANSWERS: AnswerId, Answer, VOTES: VoteId, AnswerId, Value
Its the last value that I want to have summed for each answer, and then order by this sum for each question. Making the most popular question/answer on top of the list.
Thanks in advance
I think you want this:
var questionList = new List<Question>();//Get a real list
var sortedQuestions = (from i in questionList
select new
{
i.QuestionID,
i.QuestionText,
VotesSum = i.Answers.Sum(ee => ee.Votes.Sum(ss => ss.Value))
}
).OrderByDescending(ee => ee.VotesSum);
foreach (var item in sortedQuestions)
Console.WriteLine(item.QuestionText + " " + item.VotesSum);
Asumming your classes are like these
class Vote
{
public int VoteID { get; set; }
public int Value { get; set; }
}
class Answer
{
public int AnswerID { get; set; }
public string AnswerText { get; set; }
public List<Vote> Votes = new List<Vote>();
}
class Question
{
public int QuestionID { get; set; }
public string QuestionText { get; set; }
public List<Answer> Answers = new List<Answer>();
}
Here's a way to get what you want:
var query = questions.Select(q =>
new { q.QuestionText,
Answers = q.Answers.Select(a =>
new { a.AnswerText,
Votes = a.Votes.Sum(v => v.Value)
})
})
.Select(q =>
new { q.QuestionText,
Votes = q.Answers.Sum(a => a.Votes),
Answers = q.Answers.OrderByDescending(a => a.Votes)
})
.OrderByDescending(q => q.Votes);
As you see, the votes are summed at two levels, Answer and Question and sorted in descending order.
Related
I want to display related data from second table with each value in first table
i have tried this query
public ActionResult Index()
{
List<EmployeeAtt> empWithDate = new List<EmployeeAtt>();
var employeelist = _context.TblEmployee.ToList();
foreach (var employee in employeelist)
{
var employeeAtt = _context.AttendanceTable
.GroupBy(a => a.DateAndTime.Date)
.Select(g => new EmployeeAtt
{
Date = g.Key,
Emp_name = employee.EmployeeName,
InTime = g.Any(e => e.ScanType == "I") ? g.Where(e =>
e.ScanType == "I").Min(e =>
e.DateAndTime.ToShortTimeString())
.ToString() : "Absent",
OutTime = g.Any(e => e.ScanType == "O") ? g.Where(e =>
e.ScanType == "O").Max(e =>
e.DateAndTime.ToShortTimeString())
.ToString() : "Absent"
});
empWithDate.AddRange(employeeAtt);
}
return View(empWithDate);
}
Here is my attendance Table
AttendanceTable
Results
I want to display the shortest time with "I" Column value against each employee and last time with "O" Column value as out time. I think i am not using AddRange() at proper place. Where it should go then?
public partial class TblEmployee
{
public TblEmployee()
{
AttendanceTable = new HashSet<AttendanceTable>();
}
public int EmpId { get; set; }
public string EmployeeName { get; set; }
public virtual ICollection<AttendanceTable> AttendanceTable { get; set; }
}
public partial class AttendanceTable
{
public int Id { get; set; }
public int AttendanceId { get; set; }
public int EmployeeId { get; set; }
public string ScanType { get; set; }
public DateTime DateAndTime { get; set; }
public virtual TblEmployee Employee { get; set; }
}
The actual problem is not related to AddRange(), you need a where clause before GroupBy() to limit attendances (before grouping) to only records related to that specific employee, e.g.
_context.AttendanceTable
.Where(a => a.Employee == employee.EmployeeName)
.GroupBy(a => a.DateAndTime.Date)
...
Depended on your model, it is better to use some kind of ID instead of EmployeeName for comparison if possible.
Also you can use SelectMany() instead of for loop and AddRange() to combine the results into a single list. like this:
List<EmployeeAtt> empWithDate = _context.TblEmployee.ToList()
.SelectMany(employee =>
_context.AttendanceTable
.Where(a => a.Employee == employee.EmployeeName)
.GroupBy(a => a.DateAndTime.Date)
.Select(g => new EmployeeAtt
{
...
})
);
...
I am having a difficult time finding a proper Linq query to utilize the group output.
I want to populate an existing students List where Student class has 2 properties ID and and int[] Repeats array (can be a list too) to keep how many times they took any of the 4 lectures (L101,L201,L202,L203). So if student takes L101 twice, L202 and L203 once, and but didn't take L201 this should be {2,0,1,1,}
class Student{
public string ID{get;set;}
public int[] Repeats{get;set;} //int[0]->L101, int[1]->L201...
}
In my main class I do this basic operation for this task:
foreach (var student in students)
{
var countL101 = from s in rawData
where student.Id==s.Id & s.Lecture =="L101"
select; //do for each lecture
student.Repeats = new int[4];
student.Repeats[0] = countL101.Count(); //do for each lecture
}
This works; but I wonder how do you make it practically using Linq in case where there are 100s of lectures?
I am using Lamba Expressions rather than query syntax. Then assuming rawData is IEnumerable<T> where T looks something like...
class DataRow
{
/// <summary>
/// Id of Student taking lecture
/// </summary>
public string Id { get; set; }
public string Lecture { get; set;}
}
Then you could do something like...
var lectures = rawData.Select(x => x.Lecture).Distinct().ToList();
int i = 0;
lectures.ForEach(l =>
{
students.ForEach(s =>
{
if (s.Repeats == null)
s.Repeats = new int[lectures.Count];
s.Repeats[i] = rawData.Count(x => x.Id == s.Id && x.Lecture == l);
});
i++;
});
Now if Repeats could just be of type IList<int> instead of int[] then...
var lectures = rawData.Select(x => x.Lecture).Distinct().ToList();
lectures.ForEach(l =>
{
students.ForEach(s =>
{
if (s.Repeats == null)
s.Repeats = new List<int>();
s.Repeats.Add(rawData.Count(x => x.Id == s.Id && x.Lecture == l));
});
});
Things are further simplified if Repeats could just be instantiated to a new List<int> in the Student constructor...
class Student
{
public Student()
{
Repeats = new List<int>();
}
public string Id { get; set; }
public IList<int> Repeats { get; private set; }
}
Then you can do it in one line...
rawData.Select(x => x.Lecture).Distinct().ToList()
.ForEach(l =>
{
students.ForEach(s =>
{
s.Repeats.Add(rawData.Count(x => x.Id == s.Id && x.Lecture == l));
});
});
I have been struggling with this for several days. I need to populate a dropdownlistfor with genres.
My MovieRepository to grab the genres:
public IQueryable<Movies> MoviesAndGenres
{
get { return db.Movies.Include(m => m.parentGenre); }
}
My movie model
public virtual Genres parentGenre { get; set; }
Genre Model:
public class Genres
{
public Genres()
{
this.movies = new HashSet<Movies>();
}
[Key]
public int genreId { get; set; }
[Required(ErrorMessage = "A genre name is required")]
[StringLength(25)]
public String genreName { get; set; }
public ICollection<Movies> movies { get; set; }
}
I am trying to pass in the genres with a select list, but I am getting a LINQ to Entities does not recognize the System.String To String() Method, and this method cannot be translated to a stored expression.
Movies Controller, addMovie action:
ViewBag.Genres = movieRepository.MoviesAndGenres.Select(m => new SelectListItem
{
Text = m.parentGenre.genreName,
Value = m.parentGenre.genreId.ToString()
}).ToList();
return View();
View:
#Html.DropDownListFor(m => m.parentGenre, (SelectList)ViewBag.Genres)
Any help would be greatly appreciated!
Update:
Repository:
public IQueryable<Genres> MoviesAndGenres
{
get { return db.Genres; }
}
Controller:
var x = movieRepository.MoviesAndGenres.Select(m => new
{
Text = m.genreName,
Value = m.genreId
});
ViewBag.Genres = new SelectList(x);
return View();
View:
#Html.DropDownListFor(m => m.parentGenre, (SelectList)ViewBag.Genres)
Since you're retrieving all of the records anyways, you can just do this.
ViewBag.Genres = movieRepository.MoviesAndGenres.AsEnumerable()
.Select(m => new SelectListItem
{
Text = m.parentGenre.genreName,
Value = m.parentGenre.genreId.ToString()
});
You would also need to change your view to:
#Html.DropDownListFor(m => m.parentGenre, new SelectList(ViewBag.Genres))
Actually, a better approach would probably be this, since then it only retrieves the specific columns you need:
var x = movieRepository.MoviesAndGenres.Select(m => new
{
Text = m.parentGenre.genreName,
Value = m.parentGenre.genreId
});
ViewBag.Genres = new SelectList(x)
Also, the ToList() is no longer required because it's already in a an immediate state.
im just trying to make a join from two entities.
the two entieties are as folows:
public partial class AnswerSet
{
public int Id { get; set; }
public string Ans { get; set; }
public bool IsTrue { get; set; }
public int QuestionId { get; set; }
public virtual QuestionSet QuestionSet { get; set; }
}
and
public partial class QuestionSet
{
public QuestionSet()
{
this.AnswerSets = new HashSet<AnswerSet>();
}
public int Id { get; set; }
public string Quest { get; set; }
public virtual ICollection<AnswerSet> AnswerSets { get; set; }
}
So, there are a question and an Answer Entity on the database. 1 Question has more answers (in my example 4). So now im tried this:
var v1 = db.QuestionSets
.Select(q => q)
.Where(q=> q.Id == 11)
.Join(db.AnswerSets,
q => q.Id,
a => a.QuestionId,
(a, q) => new { question = q });
So, now i have the following output when the expression is as above (see image 1):
Here i have just the Answers.
when i chage the expression to:
var v1 = db.QuestionSets
.Select(q => q)
.Where(q=> q.Id == 11)
.Join(db.AnswerSets,
q => q.Id,
a => a.QuestionId,
(q, a) => new { question = q });
then i have the following output (see image 2): (just the question, but 4 times. as many answers i have.)
So my question is, how can i join these two entities, that the Answers are a set in the QuestionSet entity?
thank you
Image 1
Image 2
You want a group join (see http://msdn.microsoft.com/en-us/library/bb311040.aspx)
var QAs =
from q in db.QuestionSets
join a in db.AnswerSets
on q.Id equals a.QuestionId into answers
select new { Question = q, Answers = answers };
In Extension Method syntax:
var QAs = db.QuestionSets
.GroupJoin(
db.AnswerSets,
q => q.Id,
a => a.QuestionId,
(q, answers) => new {Question = q, Answers = answers});
Hope that helps
PS. Use it like so:
foreach (var qa in QAs)
{
Console.WriteLine("Question #{0} has {1} answers",
qa.Question.Id, qa.Answers.Count());
}
What about leaving the Join technique for complex query and use Ef Eager Loading by using Include
var v1 = db.QuestionSets.Include(b = b.Answer);
or
var v1 = db.QuestionSets.Include("Answer");
I have a List<MyClass> and I want to sort it by DateTime CreateDate attribute of MyClass.
Is that possible with LINQ ?
Thanks
To sort the existing list:
list.Sort((x,y) => x.CreateDate.CompareTo(y.CreateDate));
It is also possible to write a Sort extension method, allowing:
list.Sort(x => x.CreateDate);
for example:
public static class ListExt {
public static void Sort<TSource, TValue>(
this List<TSource> list,
Func<TSource, TValue> selector) {
if (list == null) throw new ArgumentNullException("list");
if (selector == null) throw new ArgumentNullException("selector");
var comparer = Comparer<TValue>.Default;
list.Sort((x,y) => comparer.Compare(selector(x), selector(y)));
}
}
You can enumerate it in sorted order:
IEnumerable<MyClass> result = list.OrderBy(element => element.CreateDate);
You can also use ToList() to convert to a new list and reassign to the original variable:
list = list.OrderBy(element => element.CreateDate).ToList();
This isn't quite the same as sorting the original list because if anyone still has a reference to the old list they won't see the new ordering. If you actually want to sort the original list then you need to use the List<T>.Sort method.
Here is a sample:
using System.Collections.Generic;
using System.Linq;
namespace Demo
{
public class Test
{
public void SortTest()
{
var myList = new List<Item> { new Item { Name = "Test", Id = 1, CreateDate = DateTime.Now.AddYears(-1) }, new Item { Name = "Other", Id = 1, CreateDate = DateTime.Now.AddYears(-2) } };
var result = myList.OrderBy(x => x.CreateDate);
}
}
public class Item
{
public string Name { get; set; }
public int Id { get; set; }
public DateTime CreateDate { get; set; }
}
}
Sure the other answers with .OrderBy() work, but wouldn't you rather make your source item inherit from IComparable and just call .Sort()?
class T {
public DateTime CreatedDate { get; set; }
}
to use:
List<T> ts = new List<T>();
ts.Add(new T { CreatedDate = DateTime.Now });
ts.Add(new T { CreatedDate = DateTime.Now });
ts.Sort((x,y) => DateTime.Compare(x.CreatedDate, y.CreatedDate));