Below are the linq query. Here I want to add one condition .
Condition : If : Firstname is not empty then select list
where (d=>d.firstname=="Firstname")
else: select all list without condition
function Ponits(string Firstname)
{
pointsCore.Categories.SelectMany(c => c.Events).Select(e => new
{
e.Firstname,
e.Surname,
e.EntityNumber,
e.Eventdate
}).ToList()
}
Two options:
First, optionally use Where:
var events = pointsCore.Categories.SelectMany(c => c.Events);
if (!string.IsNullOrEmpty(firstName))
{
events = events.Where(e => e.Firstname == firstName);
}
var result = events.Select(e => new { ... });
Second: make your Where clause check firstName:
var events = pointsCore.Categories.SelectMany(c => c.Events);
.Where(e => string.IsNullOrEmpty(firstName) ||
e.Firstname == firstName)
.Select(e => new { ... });
Note that due to the lazy evaluation in LINQ, the first option won't involve fetching all the values and then querying; you're still just building up a query.
.Where(d => string.IsNullOrEmpty(Firstname) || d.firstname==Firstname)
Related
I have the following code where I get error when loading Peers:
Value cannot be null. Parameter name: source
I am using FirstOrDefault and DefaultIfEmpty methods, and inside the select statement I am also checking if the object is empty m => m == null ?. But, I cannot avoid the error. Any ideas?
ReviewRoundDTO_student results = _context.ReviewRounds
.Include(rr => rr.ReviewTasks).ThenInclude(rt => rt.ReviewTaskStatuses)
.Include(rr => rr.Submissions).ThenInclude(s => s.PeerGroup.PeerGroupMemberships).ThenInclude(m => m.User)
.Include(rr => rr.Rubric)
.Where(rr => rr.Id == reviewRoundId)
.Select(rr => new ReviewRoundDTO_student
{
Id = rr.Id,
SubmissionId = rr.Submissions.FirstOrDefault(s => s.StudentId == currentUser.Id).Id,
Peers = rr.Submissions.FirstOrDefault(s => s.StudentId == currentUser.Id)
.PeerGroup.PeerGroupMemberships.DefaultIfEmpty()
.Select(m => m == null ? new ApplicationUserDto { } : new ApplicationUserDto
{
//FullName = m.User.FullName,
//Id = new Guid(m.UserId)
}),
}).FirstOrDefault();
Try avoiding FirstOrDefault().Something construct - expression trees do not support ?. operator which you'd normally use in similar LINQ to Objects query, and EF Core currently has issues translating it correctly - if you look at the exception stack trace, most likely the exception is coming deeply from EF Core infrastructure with no user code involved.
I would recommend rewriting the LINQ query w/o such constructs, for instance something like this:
var results = _context.ReviewRounds
.Where(rr => rr.Id == reviewRoundId)
.Select(rr => new ReviewRoundDTO_student
{
Id = rr.Id,
SubmissionId = rr.Submissions
.Where(s => s.StudentId == currentUser.Id)
.Select(s => s.Id)
.FirstOrDefault(),
Peers = rr.Submissions
.Where(s => s.StudentId == currentUser.Id)
.Take(1)
.SelectMany(s => s.PeerGroup.PeerGroupMemberships)
.Select(m => new ApplicationUserDto
{
FullName = m.User.FullName,
Id = m.UserId
})
.ToList(),
})
.FirstOrDefault();
Note that Include / ThenInclude are not needed in projection queries, because they are ignored.
I have used this to pick just a single column from the collection but it doesn't and throws casting error.
ClientsDAL ClientsDAL = new DAL.ClientsDAL();
var clientsCollection= ClientsDAL.GetClientsCollection();
var projectNum = clientsCollection.Where(p => p.ID == edit.Clients_ID).Select(p => p.ProjectNo).ToString();
Method:
public IEnumerable<Clients> GetClientsCollection(string name = "")
{
IEnumerable<Clients> ClientsCollection;
var query = uow.ClientsRepository.GetQueryable().AsQueryable();
if (!string.IsNullOrEmpty(name))
{
query = query.Where(x => x.Name.Contains(name));
}
ClientsCollection = (IEnumerable<Clients>)query;
return ClientsCollection;
}
As DevilSuichiro said in comments you should not cast to IEnumerable<T> just call .AsEnumerable() it will keep laziness.
But in your case it looks like you do not need that at all because First or FirstOrDefault work with IQueryable too.
To get a single field use this code
clientsCollection
.Where(p => p.ID == edit.Clients_ID)
.Select(p => p.ProjectNo)
.First() // if you sure that at least one item exists
Or (more safe)
var projectNum = clientsCollection
.Where(p => p.ID == edit.Clients_ID)
.Select(p => (int?)p.ProjectNo)
.FirstOrDefault();
if (projectNum != null)
{
// you find that number
}
else
{
// there is no item with such edit.Clients_ID
}
Or even simpler with null propagation
var projectNum = clientsCollection
.FirstOrDefault(p => p.ID == edit.Clients_ID)?.ProjectNo;
I have a somewhat complex LINQ to SQL query that I'm trying to optimise (no, not prematurely, things are slow), that goes a little bit like this;
IQueryable<SearchListItem> query = DbContext.EquipmentLives
.Where(...)
.Select(e => new SearchListItem {
EquipmentStatusId = e.EquipmentStatuses.FirstOrDefault(s => s.DateTo == null).Id,
StatusStartDate = e.EquipmentStatuses.FirstOrDefault(s => s.DateTo == null).DateFrom,
...
});
The where clauses aren't important, they don't filter EquipmentStatuses, happy to include if someone thinks they're required.
This is on quite a large set of tables and returns a fairly details object, there's more references to EquipmentStatuses, but I'm sure you get the idea. The problem is that there's quite obviously two sub-queries and I'm sure that (among some other things) is not ideal, especially since they are exactly the same sub-query each time.
Is it possible to flatten this out a bit? Perhaps it's easier to do a few smaller queries to the database and create the SearchListItem in a foreach loop?
Here's my take given your comments, and with some assumptions I've made
It may look scary, but give it a try, with and without the ToList() before the GroupBy()
If you have LinqPad, check the SQL produced, and the number of queries, or just plug in the SQL Server Profiler
With LinqPad you could even put a Stopwatch to measure things precisely
Enjoy ;)
var query = DbContext.EquipmentLives
.AsNoTracking() // Notice this!!!
.Where(...)
// WARNING: SelectMany is an INNER JOIN
// You won't get EquipmentLive records that don't have EquipmentStatuses
// But your original code would break if such a case existed
.SelectMany(e => e.EquipmentStatuses, (live, status) => new
{
EquipmentLiveId = live.Id, // We'll need this one for grouping
EquipmentStatusId = status.Id,
EquipmentStatusDateTo = status.DateTo,
StatusStartDate = status.DateFrom
//...
})
// WARNING: Again, you won't get EquipmentLive records for which none of their EquipmentStatuses have a DateTo == null
// But your original code would break if such a case existed
.Where(x => x.EquipmentStatusDateTo == null)
// Now You can do a ToList() before the following GroupBy(). It depends on a lot of factors...
// If you only expect one or two EquipmentStatus.DateTo == null per EquipmentLive, doing ToList() before GroupBy may give you a performance boost
// Why? GroupBy sometimes confuses the EF SQL generator and the SQL Optimizer
.GroupBy(x => x.EquipmentLiveId, x => new SearchListItem
{
EquipmentLiveId = x.EquipmentLiveId, // You may or may not need this?
EquipmentStatusId = x.EquipmentStatusId,
StatusStartDate = x.StatusStartDate,
//...
})
// Now you have one group of SearchListItem per EquipmentLive
// Each group has a list of EquipmenStatuses with DateTo == null
// Just select the first one (you could do g.OrderBy... as well)
.Select(g => g.FirstOrDefault())
// Materialize
.ToList();
You don't need to repeat the FirstOrDefault. You can add an intermediate Select to select it once and then reuse it:
IQueryable<SearchListItem> query = DbContext.EquipmentLives
.Where(...)
.Select(e => e.EquipmentStatuses.FirstOrDefault(s => s.DateTo == null))
.Select(s => new SearchListItem {
EquipmentStatusId = s.Id,
StatusStartDate = s.DateFrom,
...
});
In query syntax (which I find more readable) it would look like this:
var query =
from e in DbContext.EquipmentLives
where ...
let s = e.EquipmentStatuses.FirstOrDefault(s => s.DateTo == null)
select new SearchListItem {
EquipmentStatusId = s.Id,
StatusStartDate = s.DateFrom,
...
});
There is another problem in your query though. If there is no matching EquipmentStatus in your EquipmentLive, FirstOrDefault will return null, which will cause an exception in the last select. So you might need an additional Where:
IQueryable<SearchListItem> query = DbContext.EquipmentLives
.Where(...)
.Select(e => e.EquipmentStatuses.FirstOrDefault(s => s.DateTo == null))
.Where(s => s != null)
.Select(s => new SearchListItem {
EquipmentStatusId = s.Id,
StatusStartDate = s.DateFrom,
...
});
or
var query =
from e in DbContext.EquipmentLives
where ...
let s = e.EquipmentStatuses.FirstOrDefault(s => s.DateTo == null)
where s != null
select new SearchListItem {
EquipmentStatusId = s.Id,
StatusStartDate = s.DateFrom,
...
});
Given that you don't test for null after calling FirstOrDefault(s => s.DateTo == null) I assume that:
either for each device there is always a status with DateTo == null or
you need to see only devices which have such status
In order to do so you need to join EquipmentLives with EquipmentStatuses to avoid subqueries:
var query = DbContext.EquipmentLives
.Where(l => true)
.Join(DbContext.EquipmentStatuses.Where(s => s.DateTo == null),
eq => eq.Id,
status => status.EquipmentId,
(eq, status) => new SelectListItem
{
EquipmentStatusId = status.Id,
StatusStartDate = status.DateFrom
});
However, if you do want to perform a left join replace DbContext.EquipmentStatuses.Where(s => s.DateTo == null) with DbContext.EquipmentStatuses.Where(s => s.DateTo == null).DefaultIfEmpty().
I'm trying to select multiple columns not in a group by using linq - c#.
Using linq, I'm trying to group by ISNULL(fieldOne,''),ISNULL(fieldTo,'') and then select field_One, field_Two, field_Three for each group. So for each row that the group by would return, I want to see numerous rows.
So far I have the following, but can't seem to select all the needed columns.
var xy = tableQueryable.Where(
!string.IsNullOrEmpty(cust.field_One)
|| ! string.IsNullOrEmpty(ust.field_Two)
).GroupBy(cust=> new { field_One= cust.field_One ?? string.Empty, field_Tow = cust.field_Two ?? string.Empty}).Where(g=>g.Count()>1).AsQueryable();
Can somebody help pls?
You are pretty much there - all you are missing is a Select from the group:
var xy = tableQueryable
.Where(!string.IsNullOrEmpty(cust.first_name) || ! string.IsNullOrEmpty(ust.lastName))
.GroupBy(cust=> new { first_name = cust.first_name ?? string.Empty, last_name = cust.last_name ?? string.Empty})
.Where(g=>g.Count()>1)
.ToList() // Try to work around the cross-apply issue
.SelectMany(g => g.Select(cust => new {
Id = cust.Id
, cust.FirstName
, cust.LastName
, cust.RepId
}));
Select from each group does the projection of the fields that you want, while SelectMany dumps all the results into a flat list.
Would this work for you?
var groupsWithDuplicates = tableQueryable
.Where(c => !string.IsNullOrWhiteSpace(c.first_name) || !string.IsNullOrWhiteSpace(c.last_name))
.GroupBy(c => new { FirstName = c.first_name ?? "", LastName = c.last_name ?? "" })
.Where(group => group.Count() > 1) // Only keep groups with more than one item
.ToList();
var duplicates = groupsWithDuplicates
.SelectMany(g => g) // Flatten out groups into a single collection
.Select(c => new { c.first_name, c.last_name, c.customer_rep_id });
For me I have used following query to do the filter Customer and get the customer records group by the JobFunction. In my case the issue get resolved after adding the .AsEnumerable() after the where solve the problem.
var query = _context.Customer
.Where(x => x.JobTitle.ToUpper().Contains(searchText.ToUpper())).AsEnumerable()
.GroupBy(item => item.JobFunction,
(key, group) => new {
JobFunction = key,
CustomerRecords = group.ToList().Select(c => c).ToList()
})
.ToList();
I am trying to build a query where there is one student name then a nested collection of clubs he belongs to. I want to organize this collection with OrderByDescending. I am stuck with what to provide to the parenthesis.
public void GetStudentsClubNameRev()
{
try
{
using (SchoolContainer = new SchoolContainer())
{
var query = from student in SchoolContainer.Students
select new
{
StudentName = student.Name,
ClubName = student.StudentClubMatches
.Where(s =>s.StudentId == student.Id)
.Select(c => c.Club.Name)
.OrderByDescending(o => "Name")
};
}
}
catch (Exception ex)
{
}
}
In .OrderByDescending(o => "Name") I don't know what my predicate is. I want to say orderbydescending on the Name which is club name. But I get errors because I don't think I understand what it wants.
After you've selected "Club.Name", the current enumerable is just a string. You just want a pass-through selector:
.Select(c => c.Club.Name)
.OrderByDescending(name => name)
If you OrderByDescending before Select you could also do this:
var query = from student in SchoolContainer.Students
select new
{
StudentName = student.Name,
ClubName = student.StudentClubMatches
.Where(s =>s.StudentId == student.Id)
.OrderByDescending(c => c.Club.Name)
.Select(c => c.Club.Name)
};
Cheers
To sort by a property you should use the following:
Code:
.OrderByDescending(o => o.Name)