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how to apply join or innerquery to connect two table

Here MyChildTable contains only id and the parent table contains id + name.
I have written a query to fetch the existing data from the table
await _dbContext.MyChildTable
.Where(c => c.CustomerId == **(select customerid from tableParent where customername= reqcustomername)**
Here i want to match customerId with the matching customer id from the second table ie tableParent.How to replace the query in to linq to get the proper record.select customerid from tableParent where customername= reqcustomername i want to replace this selection

I don't understand what you mean
so my maybe answer error
LINQ
using (entity entityData = new entity())
{
var checkqry2 = from T1 in entityData.MyChildTable.AsNoTracking()
join T2 in entityData.tableParent on
T1.CustomerId equals T2.customerid
where T1.customerid == "ID" && T2.customername == reqcustomername
group new { T2.customerid, T2.customername } by new { T1.customerid, T1.customername } into c
orderby c.Key.customerid
select new { customername=c.Key.customername,
customerid=c.Key.customerid,
};
}
you can try entity lambda
entity lambda
using (entity entityData = new entity())
{
var query1 = entityData.MyChildTable
.Join(entityData.tableParent , o => o.CustomerId , p => p.CustomerId , (o, p) => new
{
o.CustomerId,
p.customername,
}).Where(o => o.CustomerId == "123" && o.customername == "name").ToList();
}

Here I want to match customerId with the matching customer id from the
second table ie tableParent.How to replace the query in to linq to get
the proper record.select customerid from tableParent where
customername= reqcustomername i want to replace this selection
Well, lot of way around to handle this kind of scenario. Most easy and convenient way you could consider by using linq join or linq Enumerable which you can implement as following:
Sample Data:
var childList = new List<ChildTable>()
{
new ChildTable(){ Id =101,ChildName = "Child-A",CustomerId = 202},
new ChildTable(){ Id =102,ChildName = "Child-B",CustomerId = 203},
new ChildTable(){ Id =103,ChildName = "Child-C",CustomerId = 202},
new ChildTable(){ Id =104,ChildName = "Child-D",CustomerId = 204},
};
var parentList = new List<ParentTable>()
{
new ParentTable(){ Id =301,ParentName = "Parent-A",CustomerId = 202},
new ParentTable(){ Id =302,ParentName = "Parent-B",CustomerId = 202},
new ParentTable(){ Id =303,ParentName = "Parent-C",CustomerId = 203},
new ParentTable(){ Id =304,ParentName = "Parent-D",CustomerId = 205},
};
Linq Query:
Way One:
var findMatchedByCustId = from child in childList
where (from parent in parentList select parent.CustomerId)
.Contains(child.CustomerId)
select child;
Way Two:
var usingLinqJoin = (from parent in parentList
join child in childList on parent.CustomerId equals child.CustomerId
select parent).ToList().Distinct();
Output:
Note: If you need more information you could check our official document for Linq join and Linq Projction here.

How to pull one column from second table in Linq query with join

I have the following linq query that works fine, but I am wanting to pull one column (CompanyId) from context.Emps into the results along with the results from context.BillingProfiles. How would I modify the select (select prof) below to include said column?
var query = (from prof in context.BillingProfiles
join emp in context.Emps on prof.ID equals emp.ID
join grp in context.BillingGroups on prof.GroupID equals grp.GroupID
where (prof.EndDate == null) && (grp.System == "sysGrp") && (prof.ID == id)
select prof).Distinct()
.Select(x => new OpId()
{
id = x.ID,
GroupId = x.GroupID,
OpId = x.OpID,
StartDate = x.StartDate,
EndDate = x.EndDate,
AddedOn = x.AddedOn,
AddedBy = x.AddedBy,
RemovedOn = x.RemovedOn,
RemovedBy = x.RemovedBy,
Prodid = x.ProdID,
});
Thanks

Project an anonymous object containing those too:
var query = from prof in context.BillingProfiles
join emp in context.Emps on prof.ID equals emp.ID
join grp in context.BillingGroups on prof.GroupID equals grp.GroupID
where prof.EndDate == null && prof.ID == id && grp.System == "sysGrp"
select new { prof, emp.CompanyId, grp };

sql query to c# using northwind DB

using the northwind DB, i have to make a query to get employeename, amount of orders per employee and average price of those orders
this is what the query looks like in SQL
SELECT TOP 10
a.LastName, a.FirstName, amountOfOrders = COUNT(DISTINCT b.OrderID), AveragePricePerOrder = SUM(c.Quantity*c.UnitPrice) /COUNT(DISTINCT b.OrderID)
FROM Employees a join orders b on (a.EmployeeID = b.EmployeeID)
join [Order Details] c on b.OrderID = c.OrderID
Group BY a.EmployeeID, a.LastName, a.FirstName
ORDER BY amountOfOrders Desc
this runs fine but I have to make this in c# and I am a little stuck
So far, I have got this
var query_rx = (from c in ctx.Employees
join or in ctx.Orders on c.EmployeeID equals or.EmployeeID
join ord in ctx.Order_Details on or.OrderID equals ord.OrderID
group c by new
{
c.EmployeeID,
c.LastName,
c.FirstName,
amount = c.Orders.Count
} into c
orderby c.Key.amount descending
select new
{
c.Key.LastName,
c.Key.FirstName,
amountOfOrders = c.Key.amount
}).Take(10);
"edit" I am having trouble working the average in, tried a lot of things but I can't get it to work
"edit" I have changed the query a bit with help from Dohnal's suggestion.
This looks almost exactly like what i want in terms of columns, except that the field lastname and firstname are blank, even with ToString
var query_rx = (from or in ctx.Order_Details
join ord in ctx.Orders on or.OrderID equals ord.OrderID
group or by new
{
ord.EmployeeID
} into c
orderby c.Select(x => x.OrderID).Distinct().Count() descending
select new
{
Lastname = (from emp in ctx.Employees
where c.Key.EmployeeID == emp.EmployeeID
select emp.LastName),
Firstname = (from emp in ctx.Employees
where c.Key.EmployeeID == emp.EmployeeID
select emp.FirstName),
c.Key.EmployeeID,
AmountOfOrders = c.Select(x => x.OrderID).Distinct().Count(),
AveragePricePerOrder = c.Sum(x => x.Quantity * x.UnitPrice) / c.Select(x => x.OrderID).Distinct().Count()
}).Take(10);

Try this query:
var query = (from emp in ctx.Employers
join order in ctx.Orders on emp.EmployeeID equals order.EmployerID
join orderDet in ctx.Order_Details on order.OrderID equals orderDet.OrderID
group new { emp, order, orderDet }
by new { emp.FirstName, emp.LastName, emp.EmployeeID, order.OrderID }
into orderGroup
let a = new
{
orderGroup.Key.EmployeeID,
orderGroup.Key.FirstName,
orderGroup.Key.LastName,
orderGroup.Key.OrderID,
sum1 = orderGroup.Sum(x => x.orderDet.Quantity * x.orderDet.UnitPrice),
}
group a by new { a.FirstName, a.LastName, a.EmployeeID } into empGroup
let a2 = new
{
empGroup.Key.FirstName,
empGroup.Key.LastName,
sum = empGroup.Sum(x => x.sum1),
count = empGroup.Count()
}
orderby a2.count descending
select new
{
a2.FirstName,
a2.LastName,
amountOfOrders = a2.count,
AveragePricePerOrder = a2.sum / a2.count
}).Take(10);

Select Values from two tables using Linq

Hi I know this has been asked plenty of times, I'm not getting it through my skull
How to select Values from several tables
I made these two Linq queries
First
r = (from d in db.stageManagers
where d.profileID == UserID && d.verticalID == VerticalID
select new StageModels()
{
UserId = d.profileID,
VerticalId = (int)d.verticalID,
VerticalStageID = d.stageID
}).FirstOrDefault();
Second
r = (from d in db.stageManagerVerticals
where d.ID == r.VerticalId
select new StageModels()
{
VerticalName = d.verticalName
}
).FirstOrDefault();
I want to make them one statement since they add data to one model and the tables they query have a Pk Fk relationship
In the first block d.verticalId is what I use to get the value(Name) in the secondblock, d.verticalId is primary key to stageManagerVerticals and foreign key in stageManager, How can i join these queries ?
I tried this:
r = (from d in db.stageManagers
join c in db.stageManagerVerticals on d.stageID equals c.ID
where d.profileID == UserID && d.verticalID == VerticalID
select new StageModels()
{
UserId = d.profileID,
VerticalId = (int)d.verticalID,
VerticalStageID = d.stageID;
VerticalName = c.verticalName
}
).FirstOrDefault();

try with JOIN in LINQ to select values from more than one table
eg:
var innerJoinQuery =
from category in categories
join prod in products on category.ID equals prod.CategoryID
select new { ProductName = prod.Name, Category = category.Name };

var leftOuterJoin=(c in categories
join p in products on c.ID equals p.CategoryID into t
from temp in t.DefaultIfEmpty()
select new { ProductName = p.Name, Category = c.Name }
).ToList();

You can utilize the Navigational Properties,
var r = db.stageManagers.Where(x => x.profileID == UserID && x.verticalID == VerticalID).
Select(
d => new StageModels() {
UserID = d.profileID,
VerticalID = (int)d.verticalID,
VerticalStageID = d.stageID,
VerticalName = d.stageManagerVertical.verticalName
}
).FirstOrDefault();

Linq query with a Conditional WHERE Clause

I am new to LINQ so apologises upfront
I have the following Linq query :-
var OrdersByBranches =
from a in AllOrders
join b in AllBranchKeys
on a.BranchKey equals b.BranchKey
orderby a.Date
group a by new { a.Date, a.paymentMethod } into BranchOrderGrouped
select new
{
BranchOrderGrouped.Key.Date,
CurrencyAmount = BranchOrderGrouped.Sum(a =>
a.CurrencyAmount),
BranchOrderGrouped.Key.paymentMethod
};
I need to include a where clause in the above query ... only if a variable called
BranchKeySelected is ""
I have tried using an If Else statement and have the same above query duplicated with
one containing a where clause and one NOT. ...But When I do this .. then OrdersByBranches
is NOT available outside of the IF Statement
Would be grateful for any help
Regards
Ghost

var OrdersByBranches =
from a in AllOrders
join b in AllBranchKeys on a.BranchKey equals b.BranchKey
orderby a.Date
group a by new { a.Date, a.paymentMethod } into BranchOrderGrouped
select new {
BranchOrderGrouped.Key.Date,
CurrencyAmount = BranchOrderGrouped.Sum(a => a.CurrencyAmount),
BranchOrderGrouped.Key.paymentMethod
};
if(string.IsNullOrEmpty(BranchKeySelected ))
{
OrdersByBranches = OrdersByBranches.Where(/*blbabla*/);
}
return OrdersByBranches;

Try (and my linq is not polished)
var OrdersByBranches = from a in AllOrders
join b in AllBranchKeys on a.BranchKey equals b.BranchKey
where b.BranchKeySelected.Contains("")
orderby a.Date group a by new
{
a.Date,
a.paymentMethod
}
into BranchOrderGrouped
select new
{
BranchOrderGrouped.Key.Date,
CurrencyAmount = BranchOrderGrouped.Sum(a => a.CurrencyAmount),
BranchOrderGrouped.Key.paymentMethod
};