Develop Reference

Linq Join query returning empty dataset

I am using below code to join two tables based on officeId field. Its retuning 0 records.
IQueryable<Usage> usages = this.context.Usage;
usages = usages.Where(usage => usage.OfficeId == officeId);
var agencyList = this.context.Agencies.ToList();
var usage = usages.ToList();
var query = usage.Join(agencyList,
r => r.OfficeId,
a => a.OfficeId,
(r, a) => new UsageAgencyApiModel () {
Id = r.Id,
Product = r.Product,
Chain = a.Chain,
Name = a.Name
}).ToList();
I have 1000+ records in agencies table and 26 records in usage table.
I am expecting 26 records as a result with chain and name colums attached to result from agency table.
Its not returning anything. I am new to .net please guide me if I am missing anything
EDIT
#Tim Schmelter's solution works fine if I get both table context while executing join. But I need to add filter on top of usage table before applying join
IQueryable<Usage> usages = this.context.Usage;
usages = usages.Where(usage => usage.OfficeId == officeId);
var query = from a in usages
// works with this.context.usages instead of usages
join u in this.context.Agencies on a.OfficeId equals u.OfficeId
select new
{
Id = a.Id,
Product = a.Product,
Chain = u.Chain,
Name = u.Name
};
return query.ToList();
Attaching screenshot here
same join query works fine with in memory data as you see below
Both ways works fine if I add in memory datasource or both datasource directly. But not working if I add filter on usages based on officeId before applying join query

One problem ist that you load all into memory first(ToList()).
With joins i prefer query syntax, it is less verbose:
var query = from a in this.context.Agencies
join u in this.context.Usage on a.OfficeId equals u.OfficeId
select new UsageAgencyApiModel()
{
Id = u.Id,
Product = u.Product,
Chain = a.Chain,
Name = a.Name
};
List<UsageAgencyApiModel> resultList = query.ToList();
Edit: You should be able to apply the Where after the Join. If you still don't get records there are no matching:
var query = from a in this.context.Agencies
join u in this.context.Usage on a.OfficeId equals u.OfficeId
where u.OfficeId == officeId
select new UsageAgencyApiModel{ ... };

The following code can help to get the output based on the ID value.
Of course, I wrote with Lambda.
var officeId = 1;
var query = context.Agencies // your starting point - table in the "from" statement
.Join(database.context.Usage, // the source table of the inner join
agency => agency.OfficeId, // Select the primary key (the first part of the "on" clause in an sql "join" statement)
usage => usage.OfficeId , // Select the foreign key (the second part of the "on" clause)
(agency, usage) => new {Agency = agency, Usage = usage }) // selection
.Where(x => x.Agency.OfficeId == id); // where statement

How To Translate SQL Inner Join, Groupby Into Linq?

Here I have SQL query, now I am trying to translate it into linq but don't have any idea how to do it and got stuck in getting ChapterId from ChapterQuestion table.
Any help with translation will be grate.
Thank you
Below is my sql query
SELECT CQ.ChapterId,CQS.SetNumber,count(distinct CQ.ChapterQuestionId) as questioncount FROM
[dbo].[ChapterQuestion] AS CQ
JOIN [dbo].[ChapterQuestionSet] AS CQS ON CQ.ChapterQuestionSetId = CQS.ChapterQuestionSetId
WHERE CQ.ChapterId = 1 group by CQS.SetNumber,CQ.ChapterId
Below is my linq
var list = (from CQS in uow.Repository<ChapterQuestionSet>().GetAll().ToList()
join CQ in uow.Repository<ChapterQuestion>().FindBy(x => x.ChapterId == chapterId).ToList()
on CQS.ChapterQuestionSetId equals CQ.ChapterQuestionSetId
group CQ by CQS into G1
select new ChapterQuestionSetVM
{
ChapterQuestionSetId = G1.Key.ChapterQuestionSetId,
Count = G1.Count(t => t.ChapterQuestionSetId != null),
QuestionSetNo = $"Question set {G1.Key.SetNumber}",
ChapterId = // how do i get chapterid from ChapterQuestion
}).ToList();

This is corrected query. I hope Repository.GetAll() returns IQueryable?
This query works only with EF Core 5.x
var query =
from CQS in uow.Repository<ChapterQuestionSet>().GetAll()
join CQ in uow.Repository<ChapterQuestion>().GetAll() on CQS.ChapterQuestionSetId equals CQ.ChapterQuestionSetId
where CQ.ChapterId == 1
group CQ by new { CQS.SetNumber, CQ.ChapterId } into G1
select new ChapterQuestionSetVM
{
ChapterId = G1.Key.ChapterId
QuestionSetNo = $"Question set {G1.Key.SetNumber}",
Count = G1.Select(t => t.ChapterQuestionSetId).Distinct().Count(),
};
var list = query.ToList();

Join 2 table and group 2 field in linq

I have a very simple SQL
SELECT s.shop_code
,SUM(im.amt) sum_amt
,s.cell_no#1 shop_cell
FROM tb_sn_so_wt_mst im
,tb_cm_shop_inf s
WHERE im.shop_code = s.shop_code
GROUP BY s.shop_code, s.cell_no#1)
then i try to code linq
var listResult = from warrantyMaster in listWarrantyMasters2.Records
join shopInfo in listShopInfos
on warrantyMaster.ShopCode equals shopInfo.ShopCode
i don't know group by shop code and cell no and sum atm, any one help me out of this problem

The group by syntax with some examples is explained here group clause (C# Reference) and related links.
Here is the direct translation of your SQL query (of course the field names are just my guess since you didn't provide your classes):
var query = from im in listWarrantyMasters2.Records
join s in listShopInfos
on im.ShopCode equals s.ShopCode
group im by new { s.ShopCode, s.CellNo } into g
select new
{
g.Key.ShopCode,
g.Key.CellNo,
SumAmt = g.Sum(e => e.Amt)
};

You can try this code:
var results = from warrantyMaster in listWarrantyMasters2.Records
from shopInfo in listShopInfos
.Where(mapping => mapping.ShopCode == warrantyMaster.ShopCode )
.select new
{
ShopCode = warrantyMaster.ShopCode,
ATM = listWarrantyMasters2.ATM,
ShellNo = shopInfo.ShellNo
}
.GroupBy(x=> new { x.ShopCode, x.ShellNo })
.Select(x=>
new{
ShopCode = x.Key.ShopCode,
ShellNo = x.Key.ShellNo,
SumATM = x.Sum(item=>item.ATM)
});

Type inference failed in the call to 'Join'

I am getting the following error on the word "join" in the code below.
The type of one of the expressions in the join clause is incorrect.
Type inference failed in the call to 'Join'.
var organisationQuery = ClientDBContext.Organisations.Where(x => true);
var orderGrouped = from order in ClientDBContext.Orders.Where(x => true)
group order by order.OrganisationId into grouping
select new { Id = grouping.Key.Value, OrderCount = grouping.Count() };
var orders = from og in orderGrouped
join org in organisationQuery on og.Id equals org.Id
select(x => new OrganisationOrdersReportPoco()
{
OrganisationNameThenCode = org.Name,
TotalOrders = og.OrderCount
});
I don't see a problem with the join clause? Can anyone please advise?
Edit:
This is the piece of SQL I am attempting to write as LINQ.
SELECT grp.OrganisationId,
grp.OrderCount,
organisations.Name
FROM (select OrganisationId,
count(*) as OrderCount
from orders where 1 = 1 group by OrganisationId) grp
LEFT OUTER JOIN organisations on grp.OrganisationId = organisations.OrganisationId
WHERE 1 = 1
I have complicated where clauses on both orders and organisations... simplified for this example.

You are selecting into an anonymous type in the first query:
var orderGrouped = ..
select new { Id = grouping.Key.Value, OrderCount = grouping.Count() };
This 'breaks' the connection with order.
The join looks like it should work for Linq-to-Objects but it can't be converted into SQL.
You'll have to eliminate the anonymous type and somehow make a more direct connection.
I wonder why you don't simply go from Organisations? With a proper mapping using nav-properties it should look like:
from org in ClientDBContext.Organisations
select(x => new OrganisationOrdersReportPoco()
{
OrganisationNameThenCode = org.Name,
TotalOrders = org.Orders.Count
};
using the Id properties should be a little more involved but follow the same pattern.

(Credit to Giorgi Nakeuri)
I was confusing LAMBDA with LINQ expressions.
Replacing my select with this solved it.
select new OrganisationOrdersReportPoco()
{
OrganisationNameThenCode = org.Name,
TotalOrders = og.OrderCount
};

Linq to SQL join and group

I have two tables in my database:
Town:
userid, buildingid
Building:
buildingid, buildingname
What i want is to populate a GridView like this:
But I don't want the buildings to be shown more than once. Here is my code:
var buildings = dc.Towns
.Where(t => t.userid == userid)
.GroupJoin(dc.Buildings,
t => t.buildingid,
b => b.buildingid,
(Towns, Buildings) => new
{
BuildningName = Buildings.First().buildingname,
Count = Towns.Building.Towns.Count()
});
gvBuildings.DataSource = buildings.ToList();
gvBuildings.DataBind();
New code which works:
var buildings = (from t in dc.Towns
where t.userid == userid
join b in dc.Buildings
on t.buildingid equals b.buildingid
into j1
from j2 in j1.DefaultIfEmpty()
group j2 by j2.buildingname
into grouped
select new
{
buildingname = grouped.Key,
Count = grouped.Count()
});
gvBuildings.DataSource = buildings.ToList();
gvBuildings.DataBind();

var buildings = from t in dc.Towns
join b in dc.Buildings on t.buildingid equals b.buildingid into j1
from j2 in j1.DefaultIfEmpty()
group j2 by b.buildingname into grouped
select new { buildingname = grouped.key, Count = grouped.Count()}
I think this should do it. I have not tested it so it might give error but it will be something like this.

Wouldn't something like this do it?
Users
.Select(User => new {User, User.Building})
.GroupBy(x => x.Building)
.Select(g=> new {Building = g.Key, Count = g.Count()})

According to my experience with Linq to SQL, when the expression is becoming complicated it is better to write a stored procedure and call it with Linq to SQL. In this way you get better maintainability and upgradeability.
Rather than an option to pure SQL, I see “Linqu to SQL” as a tool to get hard typed object representation of SQL data sets. Nothing more.
Hope it helps you.