Nested selects in LINQ expression, how to? - sql

I don't know how to work with nested selects in LINQ.
How could I convert this SQl expression to LINQ?
Select i.ID, i.Impression,
(Select COUNT(ImpressionsId)
from DiaryImpressions
where DiaryPostsId = '2' AND ImpressionsId = i.ID) as Num from Impressions i

Seriously? DiaryPostsId is a string? Oh well...
from i in context.Impressions
select new {
i.ID,
i.Impressions,
Num = (from d in context.DiaryImpressions
where d.DiaryPostsId == "2"
&& d.ImpressionsId == i.ID
select d).Count()
}

from ...
select new {
i.Id,
i.Impression,
Count = context.DiaryImpressions.Count(d => d.DiaryPostsId == 2 && d.ImpressionsId == i.Id)
}
If you map your objects properly, you can use child relations directly:
Count = i.DiaryImpressions.Count(d => d.DiaryPostsId == 2)

Related

SQL Statement with inner join to LINQ

I need to convert my SQL statement to LINQ.
SELECT
dbo.Transactions.TypeRefID,
dbo.TransactionItems.ItemRefID,
SUM(dbo.TransactionItems.Quantity) AS Qty
FROM
dbo.TransactionItems
LEFT OUTER JOIN
dbo.Transactions ON dbo.TransactionItems.TransactionRefID = dbo.Transactions.TransactionID
GROUP BY
dbo.Transactions.TypeRefID, dbo.TransactionItems.ItemRefID
HAVING
(dbo.Transactions.TypeRefID = 1)
AND (dbo.TransactionItems.ItemRefID = 5)
I tried converting the above statement into LINQ and this is what I've done.
var query = from t in db.Transaction
join i in db.TransactionItem on t.TransactionID equals i.TransactionRefID
where t.TypeRefID == 1 && i.ItemRefID == 5
group i by new
{
t.TypeRefID,
i.ItemRefID
} into g
select new
{
TypeRefID = g.Key.TypeRefID,
ItemRefID = g.Key.ItemRefID,
Quantity = g.Sum(q => q.Quantity)
};
When I run my code I get error "System.Linq.Queryable.FirstOrDefault(...) returned null"
I'm using it like this
if (query != null)
string qty = query.FirstOrDefault().Quantity.ToString();
The error is called on "query.FirstOrDefault().Quantity.ToString()"
How to avoid this error?

Losing Aliases when trying to group-by rows in linq sql query, how to group-by rows in this case

I am a newbie intern way over my head, I promise I have researched this thoroughly and tried many different things. The following linq query works, but I want to group rows by last and first name and then only show the rows that appear more than once. When I un-comment out the group by statement, all my aliases below become unrecognized and changing them to the actual db.table names doesn't help.
var query = from emps in db.Employees
join c in db.Cards on emps.SbiID equals c.SbiID
where c.StateID == 0 && c.CardNumberNumeric > 100000
//group emps by new {emps.Surname, emps.Name};
//orderby grp.Count() // something like 'where grp.Count > 1
select new
{
Surname = emps.Surname,
Name = emps.Name,
CorpID = emps.Identifier,
CardNum = c.CardNumber,
CostCenter = emps.EmployeeUserField.UF13,
Supervisor = (from e in db.Employees
where
e.Identifier.Equals(emps.EmployeeUserField.UF5)
select e.Surname).FirstOrDefault()
+ ", "
+ (from e in db.Employees
where e.Identifier.Equals(emps.EmployeeUserField.UF5)
select e.Name).FirstOrDefault(),
SupervisorID = emps.EmployeeUserField.UF5,
EmpCommence = emps.CommencementDateTime,
CardCommence = c.CommencementDateTime,
WorkPhone = emps.Telephone,
State = (from cf in db.ComboFields
from sp in db.StringProperties
where cf.ComboIndex.Equals(c.StateID)
&& cf.StringID.Equals(sp.StringID)
&& cf.TableName.Equals("Card")
&& cf.FieldName.Equals("StateID")
select sp.DefaultValue).FirstOrDefault()
};
this.tagsGridView.DataSource = query;
this.tagsGridView.DataBind();
I think the problem you're running into is that you're not flattening out your groups appropriately. For example:
var duplicateEmployees = db.Employees
.GroupBy(emp => emp, new EmployeeComparer())
.Where(grp => grp.Count() > 1)
.SelectMany(grp => grp.AsEnumerable());
var duplicateEmployeeInfo =
from emps in duplicateEmployees
join c in db.Cards on emps.SbiID equals c.SbiID
where c.StateID == 0 && c.CardNumberNumeric > 100000
select new
{
... what to select
};
With:
public class EmployeeComparer : IEqualityComparer<Employee>
{
public bool Equals(Employee x, Employee y)
{
return x.Surname == y.Surname && x.Name == y.Name;
}
public int GetHashCode(Employee obj)
{
unchecked { return (17 * obj.Surname.GetHashCode()) ^ (23 * obj.Name.GetHashCode()); }
}
}
This groups the employees by name, finds the groups that have a count > 1, then returns the elements of those groups. No guarantees on performance, but this should solve your issue.

How to convert this SQL to LINQ or Lambda expression?

here's my sql query below:
Can you guys help me to convert this to a much cleaner one??
SELECT [PurchaseRequestID], [ProjectID],[FullName]
FROM PurchaseRequest
WHERE [PurchaseRequestID] IN
(SELECT [PurchaseRequestID] FROM PurchaseRequestDetail )
AND [PurchaseRequestID] NOT IN
(SELECT [PurchaseRequestID] FROM [PurchaseOrder] )
Though i have already converted this successfuly, i think this is not readable and needs to be rewritten:
var query = from a in db.PurchaseRequests
where
(from b in db.PurchaseRequestDetails
select new
{
b.PurchaseRequestID
}).Contains(new { a.PurchaseRequestID }) &&
!(from c in db.PurchaseOrders
select new
{
c.PurchaseRequestID
}).Contains(new { a.PurchaseRequestID })
select a;
thanks
you really don't need all those anonymous objects. Use the let keyword to introduce temporary variables instead of doing operations on the subqueries directly.
from a in db.PurchaseRequests
let b = from b in db.PurchaseRequestDetails select b.PurchaseRequestID
let c = from c in db.PurchaseOrders select c.PurchaseRequestID
where b.Contains(a.PurchaseRequestID) && !c.contains(a.PurchaseRequestID)
select a;
var query = from a in db.PurchaseRequests
where
db.PurchaseRequestDetails.Any(x => x.PurchaseRequestID == a.PurchaseRequestID) &&
!db.PurchaseOrders.Any(x => x.PurchaseRequestID == a.PurchaseRequestID)
select a;
If you have navigation properties set up, you can write the query like this:
IQueryable<PurchaseRequest> query =
from purchaseRequest in myDataContext.PurchaseRequests
where purchaseRequest.PurchaseRequestDetail.Any()
where !purchaseRequest.PurchaseOrder.Any()
select purchaseRequest;
Or this lambda/method style if you prefer...
IQueryable<PurchaseRequest> query2 = myDataContext.PurchaseRequests
.Where(purchaseRequest => purchaseRequest.PurchaseRequestDetail.Any())
.Where(purchaseRequest => !purchaseRequest.PurchaseOrder.Any());

Convert difficult ordered SQL statement to LINQ (edmx)

Need help with converting next statement to LINQ:
SELECT * FROM comments
WHERE good_id = '19' AND allow = '1'
ORDER BY IF(parent_id = 0, id, parent_id) DESC, id ASC
It's statement show the comment in next order list:
--Comment
--Subcomment (if parent_id != 0)
--Subcomment (if parent_id != 0)
--Comment
--Subcomment (if parent_id != 0)
etc.
But I don't know how to implement it on LINQ. Any ideas?
have not compiled this but I think I am on the right path.
var comments = from c in db.Comments
where c.good_id == 19 && c.allow = "1"
orderby myFunction(c.parent_id, c.id) descending, id ascending
select comments;
public int myFunction(int parentID, in ID)
{
return parent_id == 0 ? id : parent_id;
}
If models have relationships set up correctly then you don't need to do anything fancy
var comments = dataCoontext.Comments
.Where(c => c.GoodId = 19 &&
c.Allow = 1 &&
c.ParentId = 0) //Get top level comments
.OrderBy(c => c.Id);
foreach(var comment in comments){
Console.WriteLine("Comment:" + comment.Text);
GetSubComments(comment);
}
Then use the following
public void GetSubComments(Comment comment){
foreach(var subComment in comment.Children){ //You can apply any sub ordering to Children
Console.WriteLine("Sub comment:" + subComment.Text);
GetSubComments(subComment);
}
}

Need Linq translation for the following SQL Query

select colId,
colTaskType,
MaxID
from tblTaskType
join (
select tblCheckList.colTaskTypeID,
max(colItemNumber) MaxID
from tblCheckList
group by colTaskTypeID
) x on coltaskTypeID = tblTaskType.colID
Assuming you are using linq-to-sql and have the two tables in a datacontext.
The more or less exact translation would be:
var maxChecks = from checks in DataContext.tblChecklist
group checks by checks.colTaskTypeID into g
select new { colTaskTypeID, max = g.Group.Max(x => x.colItemNumber) };
var result = from t in DataContext.tblTaskType
join c in maxChecks on t.colTaskTypeID equals c.colTaskTypeID
select new { t.colId, t.colTaskTypeID, c.max };
But you could try:
var result = from t in DataContext.tblTaskType
select new {
t.colId,
t.colTaskTypeID,
Max = (from c in DataContext.tblChecklist
where c.colTaskTypeID == t.colTaskTypeID
select c.colItemNumber).Max() };