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Replace view SQL Server with public List<> in c#.net

I am building a c#.net web application which draws data from a SQL Server. I have a view in SQL Server based on a single table containing multiple records for the employees. At most one record can be active, but it is not necessarily the one with MAX(ID). It contains the history as well as the current status of the employees. This is some legacy I have to work with.
In order to get the correct record I group by the employee code, and total the boolean field InDienst ('currently employed'), which can be 1 at most. Based on this selection I can go back and select the correct record applying MAX(ID).
SELECT
Personeelscode_ref AS Personeelscode,
SUM(InDienst) AS InDienst
FROM dbo.tPersoneel
GROUP BY Personeelscode_ref
This works fine.
However, as I am not the only one with access to the database, I would like to move this to the c#.net controller (or a model) and apply a List<> statement in c# which replaces the view. Something like this:
public static List<tPersoneel> listEmployeeAll = EmployeeDB.tPersoneel
.GroupBy(x => x.Personeelscode_ref)
.Select( new tPersoneel
{
Personeelscode_ref as Personeelscode,
(InDienst).sum()
})
.ToList();
Can you show me what the correct c#.net code would be?
Thanks much in advance!

use this code
List<tPersoneel> listEmployeeAll = EmployeeDB.tPersoneel.GroupBy(x => x.Personeelscode_ref)
.Select(y => new {
Personeelscode = y.Key.Personeelscode_ref,
InDienst = y.Sum(x => x.InDienst)
}).ToList();
or
List<tPersoneel> listEmployeeAll = (from c in EmployeeDB.tPersoneel
group c by c.Personeelscode_ref into g
select new
{
Personeelscode = y.Key.Personeelscode_ref,
InDienst = y.Sum(x => x.InDienst)
}).ToList();

Entity Framework Core 3.1.5: How to take a table collection logic out side of a linq query to avoid client-side evaluation error?

I've a query like this
public IEnumerable<ContractInquiry> ContractInquiry(Guid itemSoldID)
{
IEnumerable<ContractInquiry> result;
using (var context = new ContractDbContext(_ctxOptions))
{
var qry = from con in context.Contracts
join product in context.ContractProducts on con.ID equals product.ContractID
join service in context.ServiceDetails on con.ID equals service.ContractID into tmpService
from service in tmpService.DefaultIfEmpty()
where product.ItemSoldID == itemSoldID
&& product.ProductStatus != ProductStatus.Deleted.ToString()
&& con.Status != Status.Deleted.ToString()
select new ContractInquiry
{
ServiceID = con.ID,
ServiceType = con.ServiceType,
ServiceDate = service.ServiceDate,
ServiceNumber = service.ServiceNumber,
ServiceManager = con.Contacts.Where(q => q.Role.Contains(ContractRole.ServiceManager.ToString()))
.OrderBy(o => o.ID).FirstOrDefault()
};
result = qry.ToList();
}
return result;
}
This query was working fine. But when we upgraded to .NET Core 3.1.5 and Entity Framework Core 3.1.5, it started throwing a client-side evaluation error:
"could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync()."
So I had to take the following line out from the query:
ServiceManager = con.Contacts.Where(q => q.Role.Contains(ContractRole.ServiceManager.ToString()))
.OrderBy(o => o.ID).FirstOrDefault()
So re-wrote the query like this:
public IEnumerable<ContractInquiry> ContractInquiry(Guid itemSoldID)
{
List<ContractInquiry> result;
using (var context = new ContractDbContext(_ctxOptions))
{
var result = (from con in context.Contracts
join product in context.ContractProducts on con.ID equals product.ContractID
join service in context.ServiceDetails on con.ID equals service.ContractID into tmpService
from service in tmpService.DefaultIfEmpty()
where product.ItemSoldID == itemSoldID
&& product.ProductStatus != ProductStatus.Deleted.ToString()
&& con.Status != Status.Deleted.ToString()
select new ContractInquiry
{
ServiceID = con.ID,
ServiceType = con.ServiceType,
ServiceDate = service.ServiceDate,
ServiceNumber = service.ServiceNumber,
Contacts = con.Contacts
}).ToList();
}
result.ForEach(con => con.Contacts.Where(q => q.Role.Contains(ContractRole.ServiceManager.ToString()))
.OrderBy(o => o.ID).FirstOrDefault();
return result;
}
Here
con.Contacts
is a table collection in Contract.cs class
I've added a property like this in ContractInquiry.cs class:
[JsonIgnore]
public IEnumerable<Contact> Contacts { set; get; }
This is working fine as well.
Question:
Doing like this will work fine but at run time, the table collection "con.Contacts" will be in memory right? And that will impact the performance of the query right if the table is a huge collection? So is there a work around for this instead of using a memory table? How can I take out the "ServiceManager = .." from the select clause in my first query?
UPDATE: Can someone answer my question?

To answer your question:
No the whole Contacts table won't be loaded into memory.
It will be slower than using a database query but unless you have a crazy amount of records you won't be able to 'humanly' measure it (obv. a stress test will point out that this may be slower by 150ms on 10000 records).
Why this is:
EF Core only loads related data and when it is needed. For example you have 1000 of these ContractInquiry records when calling .ToList(). Every one of these records contain ten contacts. Then EF Core will load only 1000*10 contacts. Due to references if any of these overlap they will share memory location and only a reference to it will be saved.
Some changes you can do to make this even faster:
Change .ToList() to .AsEnumerable(). You can do this because you only iterate over that list once, so you save a whole iteration using .AsEnumerable(). (to create a list the program must iterate over it and then you iterate over it again). Also you are returning an IEnumerable so creating a list is pointless (if you are iterating over it once, which is the case here) unless you later cast it back, which I do not recommend.
Add .AsNoTracking() in the query. I don't know how you can achieve the same thing with this type of querying (I only use Linq). This will save a lot of time because EF Core will not have to create tracking (and will also save memory).
If you would change the query to a Linq query I would be happy to have a look at it and help you optimise it.

LINQ: Is there a way to combine these queries into one?

I have a database that contains 3 tables:
Phones
PhoneListings
PhoneConditions
PhoneListings has a FK from the Phones table(PhoneID), and a FK from the Phone Conditions table(conditionID)
I am working on a function that adds a Phone Listing to the user's cart, and returns all of the necessary information for the user. The phone make and model are contained in the PHONES table, and the details about the Condition are contained in the PhoneConditions table.
Currently I am using 3 queries to obtain all the neccesary information. Is there a way to combine all of this into one query?
public ActionResult phoneAdd(int listingID, int qty)
{
ShoppingBasket myBasket = new ShoppingBasket();
string BasketID = myBasket.GetBasketID(this.HttpContext);
var PhoneListingQuery = (from x in myDB.phoneListings
where x.phonelistingID == listingID
select x).Single();
var PhoneCondition = myDB.phoneConditions
.Where(x => x.conditionID == PhoneListingQuery.phonelistingID).Single();
var PhoneDataQuery = (from ph in myDB.Phones
where ph.PhoneID == PhoneListingQuery.phonePageID
select ph).SingleOrDefault();
}

You could project the result into an anonymous class, or a Tuple, or even a custom shaped entity in a single line, however the overall database performance might not be any better:
var phoneObjects = myDB.phoneListings
.Where(pl => pl.phonelistingID == listingID)
.Select(pl => new
{
PhoneListingQuery = pl,
PhoneCondition = myDB.phoneConditions
.Single(pc => pc.conditionID == pl.phonelistingID),
PhoneDataQuery = myDB.Phones
.SingleOrDefault(ph => ph.PhoneID == pl.phonePageID)
})
.Single();
// Access phoneObjects.PhoneListingQuery / PhoneCondition / PhoneDataQuery as needed
There are also slightly more compact overloads of the LINQ Single and SingleOrDefault extensions which take a predicate as a parameter, which will help reduce the code slightly.
Edit
As an alternative to multiple retrievals from the ORM DbContext, or doing explicit manual Joins, if you set up navigation relationships between entities in your model via the navigable join keys (usually the Foreign Keys in the underlying tables), you can specify the depth of fetch with an eager load, using Include:
var phoneListingWithAssociations = myDB.phoneListings
.Include(pl => pl.PhoneConditions)
.Include(pl => pl.Phones)
.Single(pl => pl.phonelistingID == listingID);
Which will return the entity graph in phoneListingWithAssociations
(Assuming foreign keys PhoneListing.phonePageID => Phones.phoneId and
PhoneCondition.conditionID => PhoneListing.phonelistingID)

You should be able to pull it all in one query with join, I think.
But as pointed out you might not achieve alot of speed from this, as you are just picking the first match and then moving on, not really doing any inner comparisons.
If you know there exist atleast one data point in each table then you might aswell pull all at the same time. if not then waiting with the "sub queries" is nice as done by StuartLC.
var Phone = (from a in myDB.phoneListings
join b in myDB.phoneConditions on a.phonelistingID equals b.conditionID
join c in ph in myDB.Phones on a.phonePageID equals c.PhoneID
where
a.phonelistingID == listingID
select new {
Listing = a,
Condition = b,
Data = c
}).FirstOrDefault();
FirstOrDefault because single throws error if there exists more than one element.

Getting Entity Framework to eager load on Group By

I know that changing the shape of a query causes Entity Framework to ignore the include calls but is there a way I can get it to load the sub properties when I do a select many and a group by. In the following example I want to notify all the employees who have a job booked in a certain time period. Calling .ToArray() after the where only hits the database once but I am doing the SelectMany and GroupBy in memory. Is there a way I can get the SelectMany and the GroupBy to happen on the SQL server and still include the ServiceType and Ship and the Employee details?
I am looking for a way to make one SQL call to the database and end up with a list of Employees who have a job in the time period and the jobs they are assigned to.
var employeeJobs = DataContext.Jobs.
Include("ServiceType").
Include("Ship").
Include("JobEmployees.Employee").
Where(j => j.Start >= now && j.Start <= finish).
OrderBy(j => j.Start).
ToArray().
SelectMany(j => j.JobEmployees, (j, je) => new {
Job = j,
Employee = je.Employee
}).GroupBy(j => j.Employee);

The following should work:
var q = from e in DataContext.Employees
where e.Job.Start > ....
order by e.Job.Start
select new {Employee = e, Job = e.Job, Ship = e.Job.Ship, ServiceType = e.Job.ServiceType}; // No db hit yet.
var l = q.GroupBy(item=>item.Employee) // no db hit yet.
.ToList(); // This one causes a db hit.

why don't you create a view and then reference this from the EF?
, this also has the added benefit of the database server doing the work, rather than the app server.

Trying move the Include()'s to the very end after your groupby.

What is the recommended practice to update or delete multiple entities in EntityFramework?

In SQL one might sometimes write something like
DELETE FROM table WHERE column IS NULL
or
UPDATE table SET column1=value WHERE column2 IS NULL
or any other criterion that might apply to multiple rows.
As far as I can tell, the best EntityFramework can do is something like
foreach (var entity in db.Table.Where(row => row.Column == null))
db.Table.Remove(entity); // or entity.Column2 = value;
db.SaveChanges();
But of course that will retrieve all the entities, and then run a separate DELETE query for each. Surely that must be much slower if there are many entities that satisfy the criterion.
So, cut a long story short, is there any support in EntityFramework for updating or deleting multiple entities in a single query?

EF doesn't have support for batch updates or deletes but you can simply do:
db.Database.ExecuteSqlCommand("DELETE FROM ...", someParameter);
Edit:
People who really want to stick with LINQ queries sometimes use workaround where they first create select SQL query from LINQ query:
string query = db.Table.Where(row => row.Column == null).ToString();
and after that find the first occurrence of FROM and replace the beginning of the query with DELETE and execute result with ExecuteSqlCommand. The problem with this approach is that it works only in basic scenarios. It will not work with entity splitting or some inheritance mapping where you need to delete two or more records per entity.

Take a look to Entity Framework Extensions (Multiple entity updates). This project allow set operations using lambda expressions. Samples from doc:
this.Container.Devices.Delete(o => o.Id == 1);
this.Container.Devices.Update(
o => new Device() {
LastOrderRequest = DateTime.Now,
Description = o.Description + "teste"
},
o => o.Id == 1);
Digging EFE project source code you can see how automatize #Ladislav Mrnka second approach also adding setting operations:
public override string GetDmlCommand()
{
//Recover Table Name
StringBuilder updateCommand = new StringBuilder();
updateCommand.Append("UPDATE ");
updateCommand.Append(MetadataAccessor.GetTableNameByEdmType(
typeof(T).Name));
updateCommand.Append(" ");
updateCommand.Append(setParser.ParseExpression());
updateCommand.Append(whereParser.ParseExpression());
return updateCommand.ToString();
}
Edited 3 years latter
Take a look to this great answer: https://stackoverflow.com/a/12751429

Entity Framework Extended Library helps to do this.
Delete
//delete all users where FirstName matches
context.Users.Delete(u => u.FirstName == "firstname");
Update
//update all tasks with status of 1 to status of 2
context.Tasks.Update(
t => t.StatusId == 1,
t2 => new Task {StatusId = 2});
//example of using an IQueryable as the filter for the update
var users = context.Users.Where(u => u.FirstName == "firstname");
context.Users.Update(users, u => new User {FirstName = "newfirstname"});
https://github.com/loresoft/EntityFramework.Extended