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passing linq anonymous result to iqueryable object for another query

I have two tables (tbPerson and tbDataLog) where I need to return Id from one table (tbPerson) after checking certain conditions on both. After this, this result should be passed to another query. My first query returns the Id (primary key of a table) successfully and I need to pass these ids to another query so that it return me data based upon these Id. I also has an IQueryable type base object to check certain conditions to fetch data.
IQueryable<tbPerson> dataset
and I cannot changes this from Iqueryable to other as it will break other part of the code)
My first linq statement:
public static IQueryable<LogResults> GetResultsForYes()
{
Databasename ents = new Databasename();
var ids = (from f in ents.tbPerson
join g in ents.tbDataLog
on f.InfoID equals g.RefId
where g.Tag == "subscribed" && g.OldValue == "No" && g.Action == "Modified"
select new LogResults { _LogID = f.Id }).OrderBy(x => x._LogID);
return ids;
}
public class LogResults
{
public int _LogID { get; set; }
}
I access my result something like this where I can see in debugger all the Ids.
IQueryable<LogResults> log = GetResultsForYes();
Problem comes, when I tried to get records from tbPerson based upon these returned Id.
dataset=log.where(x=>x._LogID != 0);
I get this error:
Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Linq.IQueryable'. An explicit conversion exists(are you missing a cast)?
Any suggestions or some other good approach is welcome.

I love this thing about stackoverflow. when we write questions we force our brain to think more deeply and after 30 mins of posting this question, I solved it in a simple way. Sometimes we overcomplicated things!
var ids = (from f in ents.tbPerson
join g in ents.tbDataLog
on f.InfoID equals g.RefId
where g.Tag == "subscribed" && g.OldValue == "No" && g.Action == "Modified"
select new { f.Id }).ToArray();
var allId = ids.Select(x => x.Id).ToArray();
dataset = dataset.Where(x => allId.Contains(x.Id));
#ankit_sharma : I have not tested yours but will give a try and come back to you. Thanks for giving time and effort.

IQueryable<tbPerson> dataset=log.where(x=>x._LogID != 0);
The result of log.where(x=>x._LogID != 0) is an IQueryable<LogResults>, and you are trying to assign this result to dataset of type IQueryable<tbPerson>, two diferent types.
EDIT:
I see you make a join to get the tbPerson ids, and then you do a second query to get the persons. You could get the persons in the first join.
I just modify your code:
IQueryable<tbPerson> persons = from person in ents.tbPerson
join g in ents.tbDataLog
on person.InfoID equals g.RefId
where g.Tag == "subscribed" && g.OldValue == "No" && g.Action == "Modified"
select person;

Convert SQL query to LINQ or lambda expression in C# and use in EF Core

I have 3 table
Tbl_City , Tbl_GroupCities , Tbl_CtrCar .
I want to convert this SQL query to LINQ or lambda expression in C#
declare #fk_group uniqueidentifier
SELECT #fk_group= FK_Group
FROM dbo.Tbl_User
WHERE UserName='meysam'
SELECT dbo.Tbl_City.ID_City, dbo.Tbl_City.Name_City,COUNT( dbo.Tbl_CtrCar.Cur_year)
FROM dbo.Tbl_City
INNER JOIN dbo.Tbl_CtrCar ON dbo.Tbl_City.ID_City = dbo.Tbl_CtrCar.FK_City
WHERE ID_City IN (SELECT FK_City
FROM dbo.Tbl_GroupCities
WHERE Active=1 AND ID_Group=#fk_group)
GROUP BY ID_City , Name_City
I try it but it's not work
var model = _TblUser.FirstOrDefault(x => x.UserName == "sampleUserName");
var q = _TblGroupCities.Where(x => x.IdGroup == model.FkGroup && x.Active == true);
var sample2 =
(from x in _TblCity
join a in _TblGroupCities on x.IdCity equals a.FkCity
where a.Active == true && a.IdGroup == model.FkGroup
select new
{
x.IdCity,
x.NameCity
}).ToList();

Please take a look here the features you have in your query are not yet implemented. GroupBy and i think also subselects will do an
SELECT * FROM TableName
And in memory it will do the group by or even for each row a new SQL query.
Better to use the RawSql method for this purpose.
But if you realy want to learn LINQ and convert your SQL take a look at LINQPad

This issue is done. I found my problem, I don't Understand use two joins and use group by in Linq
I use this linq for the solution and run
var model = _TblUser.SingleOrDefault(x => x.UserName == type.UserName);
var q = _TblGroupCities.Where(x => x.IdGroup == model.FkGroup && x.Active == true);
tblCityViewModel = new List<MohasebKhodro.ViewModels.TblCityViewModel>();
var sample2 =
(from x in _TblCity
join a in _TblGroupCities on x.IdCity equals a.FkCity
where a.Active == true && a.IdGroup == model.FkGroup
select new
{
x.IdCity,
x.NameCity
}).ToList();
foreach (var item in sample2)
{
var er = _TblCtrCar.Where(x => x.FkCity == item.IdCity).Max(x => x.CurYear);
tblCityViewModel.Add(new MohasebKhodro.ViewModels.TblCityViewModel
{
IdCity = item.IdCity,
NameCity = item.NameCity,
MaxCurrentYear = Convert.ToString(er)
});
}

LINQ - null exception on getting certain cell value

I'm a greenhorn when it comes to LINQ. I've read some null exceptions and most of them pointed out
... in sth.AsEnumerable() ...
as root of the problem.
I've run into:
The function evaluation requires all threads to run.
I tried to retrieve
fieldname
from TrashPlaces (it has 2 fields only - id and name) by string Id I get from UserPlace record (UserPlace has 2 keys - 1 is userId that can be retrieved from AspNetUsers and the other is TrashPlace id). I've run into null problem on this LINQ code:
public ActionResult JsonResult()
{
var users = db.AspNetUsers;
//this was added, so I could root out mismatch in the queryId
var nameformyuser = User.Identity.Name;
//the null starts here and no-shock it goes further (meaning query is null and
//can't do nothing later)
var queryId = from user in users.AsEnumerable()
where user.Email == User.Identity.Name
select user.Id;
var placerecord = db.UserPlace;
var userplace = from uplace in placerecord.AsEnumerable()
where uplace.usersId == queryId.ToString()
select uplace.placesId;
var places = db.TrashPlaces;
var field = from blah in places.AsEnumerable()
where blah.Id == userplace.ToString()
select blah.nameOfThePlace;
TempData["username"] = User.Identity.Name;
TempData["fieldname"] = field.ToString();
TempData["datename"] = DateTime.Now;
List<TrashViewModel> json = (List<TrashViewModel>)TempData["jsonList"];
return View(json);
}
Would be grateful for help and or/advice what's the best approach towards cascading LINQ.
Thanks!

You could do all in one (don't enumerate to early by the way, this is not good for performance).
Not sure why you use ToString() you shouldn't have to if your ids are of the same type.
var query = from u in db.AspNetUsers
join up in db.db.UserPlace on u.Id equals up.usersId
join tp in db.TrashPlaces on up.placesId equals tp.Id
where u.Email == User.Identity.Name
select tp.nameOfThePlace;//or more data if you need to.
var result = query.FirstOrDefault(); //or query.AsEnumerable()
Then you can do a null check
if (result == null)
In your case, for TempData, you may just do
TempData["fieldname"] = result == null ? string.Empty : result;
or
TempData["fieldname"] = result;
But then you'll have to check if TempData["fieldname"] is not null before using it.
...

Proper use of StartWith and Contains in Entity Framework

I want to remove prefixes from StoreName field in Linq Linq to Entity query.
I have following query which gets list of all prefixes in table
Query1
var _prefix = context.Prefixes.Select(pre => pre.Prefix1);
I want to use this result in Query2
Query2
var objRetailer = from stores in context.RetailerStoredtls
join ret in context.RetailerContactdtls
on stores.RetailerID equals ret.RetailerID
join retreg in context.RetailerRegDates
on stores.RetailerID equals retreg.RetailerRegDateId
where (stores.IsDeleted == null || stores.IsDeleted == false)
&& (stores.CreatedDate.Value.Year == iYear || stores.ModifiedDate.Value.Year == iYear)
&& retreg.IsApproved== true
orderby stores.StoreName
select new
{
stores.StoreID,
Store = stores.StoreName,
Area = stores.StoreCity,
Zip = stores.StoreZip,
SellingCard = (storessellingcard.Contains(stores.RetailerID.Value) ? true : false)
StoreWithoutPrefix = stores.StoreName.StartsWith(<one of prefix retrieved from Query1> ? stores.StoreName : <stores.StoreName without prefix>
};
Unfortunately we have .StartWith() that take only string parameter not result of Query1, if I go with .Contains it will not check for whether it starts with or not, it just check whether string is present there. What should I do to accomplish this task?
Thanks.

You can use IndexOf, but probably you have problems with case sensitivity. So add a parameter CompareOptions.IgnoreCase

Linq - Retrieve a single value in a String

I use Asp.net 3.5 and EF 4.
I need find a specific row in my DataBase and display on a label a single value as string.
At the moment I use this code, it is working, so I find a single Object and read its properties.
var myAuthor = (from at in context.CmsAuthors
where at.AuthorId == myRow.AuthorId
select at).Single();
myAuthorNameLabel.Text = myAuthor.LastName;
I would like to know:
If there is another syntax in Linq to achieve the same result.
How to do it using Lamba?
Which approach would you suggest me?

Here's the method syntax (using lambdas)
myAuthorNameLabel.Text = context.CmsAuthors
.Where(at => at.AuthorId == myRow.AuthorId)
.Select(at => at.LastName)
.SingleOrDefault() ?? string.Empty;

You can use:
var myAuthorName =
(from at in context.CmsAuthors where at.AuthorId == myRow.AuthorId select at).Single().Select(a => a.LastName);
actually this would be even better:
var myAuthorName =
(from at in context.CmsAuthors where at.AuthorId == myRow.AuthorId select at).Select(a => a.LastName).Single();
Update
An example of how to use with Anonymous type:
var myAuthorNames =
(from at in context.CmsAuthors where at.AuthorId == myRow.AuthorId select at).Select( a => new {a.LastName, a.FirstName}).Single();