Develop Reference

EF Core, use include or again context

Since:
"Eager loading a collection navigation in a single query may cause
performance issues."
see: Source
And it is advise to use split queries with include. I wonder if instead of include in the query bellow:
var task = await context.Tasks
.Include(x => x.TaskDependencies)
.Select(x => new TaskBaseModel
{
Id = x.Id,
Name = x.Name,
Description = x.Description,
TaskDependencies= x.TaskDependencies.ToArray()
})
.SingleOrDefaultAsync(x => x.Id == _id);
I should do this:
var task = await context.Tasks
.Select(x => new TaskBaseModel
{
Id = x.Id,
Name = x.Name,
Description = x.Description,
TaskDependencies= context.TaskDependencies
.Where(y => y.TaskId == x.Id).ToArray()
})
.SingleOrDefaultAsync(x => x.Id == _id);
Anyone as any info regarding this? about performance, etc..
Regards

Both queries should have the same performance and SQL. Note that Include followed by Select is ignored by EF Core.
So, most comfortable query is:
var task = await context.Tasks
.Select(x => new TaskBaseModel
{
Id = x.Id,
Name = x.Name,
Description = x.Description,
TaskDependencies = x.TaskDependencies.ToArray()
})
.SingleOrDefaultAsync(x => x.Id == _id);

How to use GroupBy() in subqueries with LINQ?

I have pretty simple LINQ expression
IQueryable<FreeBetDTO> records = UnitOfWork.FreeBets
.Include(f => f.FreeBetCategories)
.Include(f => f.FreeBetCards)
.Where(f => f.FreeBetCards.Any(cards => cards.UserId == request.UserId))
.Select(f => new FreeBetDTO
{
FreeBetId = f.FreeBetId
LineCategories = f.FreeBetCategories
.GroupBy(g => new { g.LineCategoryID, g.Title })
.Select(c =>
new LineCategoryDTO
{
LineCategoryID = c.Key.LineCategoryID,
Title = c.Key.Title
}).AsEnumerable()
});
When I am executing it I catch the error:
System.InvalidOperationException: Unable to translate collection subquery in projection since it uses 'Distinct' or 'Group By' operations and doesn't project key columns of all of it's tables which are required to generate results on client side. Missing column: t.ID. Either add column(s) to the projection or rewrite query to not use 'GroupBy'/'Distinct' operation.
at Microsoft.EntityFrameworkCore.Query.SqlExpressions.SelectExpression.
....
The problem is here .GroupBy(g => new { g.LineCategoryID, g.Title }). If I don't group records, the error disappears.
I was trying a lot of cases with GroupBy() and Distinct(). But can't understand why this is happening. Because I just need grouping like this.

Error message says that you have to include Id column in projection. But you can't do that with GroupBy. So rewrite query into two steps (removed not needed includes):
var rawRecords = UnitOfWork.FreeBets
.Where(f => f.FreeBetCards.Any(cards => cards.UserId == request.UserId))
.Select(f => new
{
FreeBetId = f.FreeBetId
LineCategories = f.FreeBetCategories.Select(c => new { c.Id, c.LineCategoryID, c.Title })
.ToList()
})
.AsEnumerable();
var records = rawRecords
.Select(f => new FreeBetDTO
{
FreeBetId = f.FreeBetId
LineCategories = f.LineCategories.GroupBy(g => new { g.LineCategoryID, g.Title })
.Select(c =>
new LineCategoryDTO
{
LineCategoryID = c.Key.LineCategoryID,
Title = c.Key.Title
})
});
Similar query, but more optimal:
var query =
from f in UnitOfWork.FreeBets
from c in f.FreeBetCards
where f.FreeBetCards.Any(cards => cards.UserId == request.UserId)
select new { f.FreeBetId, c.LineCategoryID, c.Title };
query = query.Distinct();
var records = query.AsEnumerable()
.GroupBy(f => f.FreeBetId)
.Select(g => new FreeBetDTO
{
FreeBetId = g.Key
LineCategories = g.Select(c =>
new LineCategoryDTO
{
LineCategoryID = c.LineCategoryID,
Title = c.Title
})
.AsEnumerable()
});

How can i modify this query to leave out blanks or empty value?

This query is used to select distinct value from a table in the database
public List<SubDepartmentViewModel> GetSubDepartments()
{
var query = _db.SendersReceivers.Select(a => new SubDepartmentViewModel
{
SubDepartmentName = a.SubDepartment //column in the database
})
.Distinct().ToList();
return query;
}

var query = _db.SendersReceivers
.Where(a => !string.IsNullOrEmpty(a.SubDepartment))
.Select(a => new SubDepartmentViewModel
{
SubDepartmentName = a.SubDepartment
})
.Distinct().ToList();
This should do the trick.

LINQ Method - Optimization

I'm reading a CSV file splitting it into cols, then grouping into a new class.
It looks clunky just wondering is there is a more simple method for instance like not selecting them into the class first:
EDIT: so to clarify I'm trying to get the TimesheetHours grouped by all the other columns.
var rowList = csvFile.Rows.Select(row => row.Split(','))
.Select(cols => new UtilisationRow {
UploadId = savedUpload.Id,
FullName = cols[0],
TimesheetWorkDateMonthYear = Convert.ToDateTime(cols[1]),
TimesheetTaskJobnumber = cols[2],
TimesheetWorktype = cols[3],
TimesheetHours = Convert.ToDouble(cols[4]),
TimesheetOverhead = cols[5]
})
.GroupBy(d => new {
d.FullName,
d.TimesheetWorkDateMonthYear,
d.TimesheetTaskJobnumber,
d.TimesheetWorktype,
d.TimesheetOverhead
})
.Select(g => new UtilisationRow {
FullName = g.First().FullName,
TimesheetWorkDateMonthYear = g.First().TimesheetWorkDateMonthYear,
TimesheetTaskJobnumber = g.First().TimesheetTaskJobnumber,
TimesheetWorktype = g.First().TimesheetWorktype,
TimesheetHours = g.Sum(s => s.TimesheetHours),
TimesheetOverhead = g.First().TimesheetOverhead
})
.ToList();
Many thanks,
Lee.

The two problems in your code are that you call First() repeatedly on a group, while you should retrieve that same data from group's key, and that you are using UtilisationRow in the first Select, which should use an anonymous type instead:
var rowList = csvFile.Rows.Select(row => row.Split(','))
.Select(cols => new {
UploadId = savedUpload.Id,
FullName = cols[0],
TimesheetWorkDateMonthYear = Convert.ToDateTime(cols[1]),
TimesheetTaskJobnumber = cols[2],
TimesheetWorktype = cols[3],
TimesheetHours = Convert.ToDouble(cols[4]),
TimesheetOverhead = cols[5]
})
.GroupBy(d => new {
d.FullName,
d.TimesheetWorkDateMonthYear,
d.TimesheetTaskJobnumber,
d.TimesheetWorktype,
d.TimesheetOverhead
})
.Select(g => new UtilisationRow {
FullName = g.Key.FullName,
TimesheetWorkDateMonthYear = g.Key.TimesheetWorkDateMonthYear,
TimesheetTaskJobnumber = g.Key.TimesheetTaskJobnumber,
TimesheetWorktype = g.Key.TimesheetWorktype,
TimesheetHours = g.Sum(s => s.TimesheetHours),
TimesheetOverhead = g.Key.TimesheetOverhead
})
.ToList();
Now the "pipeline" of your method looks pretty clean:
The first Select does the initial parsing into a temporary record
GroupBy bundles matching records into a group
The final Select produces records of the required type.

LINQ to Entities does not recognize the method String.Format

I'm trying to format a double value (by showing only 2 decimals). I tried to use AsEnumerable but I keep getting this error
LINQ to Entities does not recognize the method
String.Format
var tw = workers.Select(x => new
{
Id = x.Id,
JobOpportunityFeedbacks = x.JobOpportunityFeedbacks.AsEnumerable().
Select(y => new
{
Rating = String.Format("0.00",y.Rating),
Feedback = y.Feedback
});

You have to do the AsEnumerable outside of your initial Select
var tw = workers.Select(x => new
{
Id = x.Id,
JobOpportunityFeedbacks = x.JobOpportunityFeedbacks
.Select(y => new
{
y.Rating,
y.Feedback
})
})
.AsEnumerable()
.Select(x => new
{
x.Id,
JopOpertunityFeedbacks = x.JobOpportunityFeedbacks
.Select(y => new
{
Rating = String.Format("0.00",y.Rating),
y.Feedback
})
});

Use SqlFunctions class - I didn't try this but should work.
var tw = workers.Select(x => new
{
Id = x.Id,
JobOpportunityFeedbacks = x.JobOpportunityFeedbacks.AsEnumerable().
Select(y => new
{
Rating = SqlFunctions.StringConvert(y.Rating, 4, 2)
Feedback = y.Feedback
});
https://msdn.microsoft.com/en-us/library/dd487158(v=vs.110).aspx