I have the following problem. In my database table I have a coloum with the name ItemDaysNext (the coloumn is an integer). The value is ever null and this is ok....
I would like use this coloumn after for a sort value...
This satement works fine:
var query = from item in items
let today = DateTime.Today
let birthday = item.ItemDate
let next = new DateTime(today.Year, birthday.Month, birthday.Day)
let next2 = next < today ? next.AddYears(1) : next
orderby (next2 - today).Days ascending
select item;
But I would like use the result from "(next2 - today).Days" into the ItemDaysNext because then I can sort after better a Listbox because I can bind the value...
This statement doesn't work and I become a compiler error message (InvalidCastException)
var query = from item in items
let today = DateTime.Today
let birthday = item.ItemDate
let next = new DateTime(today.Year, birthday.Month, birthday.Day)
let next2 = next < today ? next.AddYears(1) : next
orderby (next2 - today).Days ascending
select new { ItemDaysNext = (next2 - today).Days };
How can I make the correct Query????
Best regards for all answers.
The only way I can replicate something similar to your problem is making the column "ItemDate" nullable and putting a null value in the database. This is easily fixed by assigning birthday to something else when null eg: line 3 let birthday = item.END_DATE ?? DateTime.MaxValue
Related
I have a database table with a datetime column and I simply want to count how many records per day going back 3 months. I am currently using this query:
var minDate = DateTime.Now.AddMonths(-3);
var stats = from t in TestStats
where t.Date > minDate
group t by EntityFunctions.TruncateTime(t.Date) into g
orderby g.Key
select new
{
date = g.Key,
count = g.Count()
};
That works fine, but the problem is that if there are no records for a day then that day is not in the results at all. For example:
3/21/2008 = 5
3/22/2008 = 2
3/24/2008 = 7
In that short example I want to make 3/23/2008 = 0. In the real query all zeros should show between 3 months ago and today.
Fabricating missing data is not straightforward in SQL. I would recommend getting the data that is in SQL, then joining it to an in-memory list of all relevant dates:
var stats = (from t in TestStats
where t.Date > minDate
group t by EntityFunctions.TruncateTime(t.Date) into g
orderby g.Key
select new
{
date = g.Key,
count = g.Count()
}).ToList(); // hydrate so we only query the DB once
var firstDate = stats.Min(s => s.date);
var lastDate = stats.Max(s => s.date);
var allDates = Enumerable.Range(1,(lastDate - firstDate).Days)
.Select(i => firstDate.AddDays(i-1));
stats = (from d in allDates
join s in stats
on d equals s.date into dates
from ds in dates.DefaultIfEmpty()
select new {
date = d,
count = ds == null ? 0 : ds.count
}).ToList();
You could also get a list of dates not in the data and concatenate them.
I agree with #D Stanley's answer but want to throw an additional consideration into the mix. What are you doing with this data? Is it getting processed by the caller? Is it rendered in a UI? Is it getting transferred over a network?
Consider the size of the data. Why do you need to have the gaps filled in? If it is known to be returning over a network for instance, I'd advise against filling in the gaps. All you're doing is increasing the data size. This has to be serialised, transferred, then deserialised.
If you are going to loop the data to render in a UI, then why do you need the gaps? Why not implement the loop from min date to max date (like D Stanley's join) then place a default when no value is found.
If you ARE transferring over a network and you still NEED a single collection, consider applying D Stanley's resolution on the other side of the wire.
Just things to consider...
First Table is the View and Second is the result I want
This below query works fine
List<BTWStudents> students = (from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
select new BTWStudents
{
StudentId = V.StudentId
Amount= V.PaymentMethod == "Cashier Check" ? V.Amount: "0.00"
}).Distinct().ToList();
But I changed it to List to add string formatting(see below)
List<BTWStudents> students = (from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
select new {V}).ToList().Select(x => new BTWStudents
{
StudentId = V.StudentId
Amount= V.PaymentMethod == "Cashier Check" ? String.Format("{0:c}",V.Amount): "0.00"
}).Distinct().ToList();
With this Second Query I get this
Why is distinct not working in the second query?
When working with objects (in your case a wrapped anonymous type because you are using Select new {V} rather than just Select V), Distinct calls the object.Equals when doing the comparison. Internally, this checks the object's hash code. You'll find in this case, the hash code of the two objects is different even though the fields contain the same values. To fix this, you will need to override Equals on the object type or pass a custom IEqualityComparer implementation into the Distinct overload. You should be able to find a number of examples online searching for "Distinct IEqualityComparer".
Try this (moved your distinct to the first query and corrected your bugged if/then/else):
List<BTWStudents> students = (from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
select new {V}).Distinct().ToList().Select(x => new BTWStudents
{
classId = V.Class.HasValue ? V.Class.Value : 0,
studentName = V.StudentName,
paymentAmount = V.PaymentMethod == "Cashier Check" ? String.Format("{0:c}",x.V.AmountOwed): "0.00"
}).ToList();
You can get around using Distinct all together if you Group by StudentID
var studentsGroupedByPayment =
(from V in db.vwStudentCoursesSD
where classIds.Contains(V.Class.Value)
group V by V.StudentId into groupedV
select new
{
StudentID = groupedV.Key,
Amount = string.Format("{0:C}",
groupedV.First().PaymentMethod == "Cashier Check" ?
groupedV.First().Amount : 0.0)
}
).ToList();
I am having trouble with the following piece of code. Before I paste it, Let me give a bit of history on what should happen.
I have a model containing 2 fields of interest at the moment, which is the name of the order the customer placed, and the date at which he/she placed it. A pre-calculated date will be used to query the dateplaced field (and should only query the dates , and not the time). The query counts the amount of duplicates that occur in the MondayOrder field, and groups them together. Now , when I exclude the where clause which should query the dates, the query runs great. However, The goal of this query is to count the amount of orders for the following week based on the date the order has been placed.
List<string> returnlist = new List<string>();
DateTime dt = getNextWeekMondaysDate().Date;
switch (day)
{
case DayOfWeek.Monday:
{
var CountOrders =
from x in Data.EntityDB.Orders
group x by x.MondayOrder into m
let count = m.Count()
select new
{
MondayOrderItem = m.Key, Amount = count
};
foreach (var item in CountOrders)
{
returnlist.Add(item.MondayOrderItem + " : " +
item.Amount);
}
}
break;
The getNextWeekMondaysDate() method has an overload which I can use, where if I supply it a date, it will get the following Monday's date from the parameter given. The problem is though, LINQ does not accept queries such as the following:
var CountOrders =
from x in Data.EntityDB.Orders
where getNextWeekMondaysDate(x.DatePlaced.Value).Date == dt
group x by x.MondayOrder into m
let count = m.Count()
select new { MondayOrderItem = m.Key, Amount = count };
This is exactly what I must achieve. Is there any workaround for this situation?
UPDATE
Here is the exception I get when I try the 2nd query.
LINQ to Entities does not recognize the method 'System.DateTime getNextWeekMondaysDate(System.DateTime)' method, and this method cannot be translated into a store expression.
You cannot do this directly, as user-defined method calls cannot be translated to SQL by the EF query provider. The provider recognizes a limited set of .NET methods that can be translated to SQL and also a number of canonical functions as well. Anything that cannot be expressed using these methods only is off-limits unless you write your own query provider (which is only theoretically an option).
As a practical workaround, you can calculate an appropriate range for x.DatePlaced.Value in code before the query and then use specific DateTime values on the where clause.
As an intellectual exercise, note that this method is recognized by the query provider and can be used as part of the expression. So this abomination should work too:
var CountOrders =
from x in Data.EntityDB.Orders
where EntityFunctions.AddDays(
x.DatePlaced.Date.Value,
(9 - DateAndTime.DatePart(DateInterval.WeekDay, x.DatePlaced.Value)) % 7)
.Date == dt
group x by x.MondayOrder into m
let count = m.Count()
select new { MondayOrderItem = m.Key, Amount = count };
Linq to Entities doesn't know how to convert arbitrary C# methods into SQL - it's not possible in general.
So, you have to work with the methods it does understand.
In this case, you could do something like this:
DateTime weekBegin = CalculateWeekBegin( dt );
DateTime weekEnd = CalculateWeekEnd( dt );
var CountOrders =
from x in Data.EntityDB.Orders
where x.DatePlaced.Value >= weekBegin && x.DatePlaced.Value < weekEnd
group x by x.MondayOrder into m
let count = m.Count()
select new { MondayOrderItem = m.Key, Amount = count });
I'm having a bit trouble with a query in Linq to Entities which I hope someone can shed a light on :-) What I'm trying to do is to create a query that joins three tables.
So far it works, but since the last table I'm trying to join is empty, the result of the query doesn't contain any records. When I remove the last join, it gives me the right results.
My query looks like this:
var query = from p in db.QuizParticipants
join points in db.ParticipantPoints on p.id
equals points.participantId into participantsGroup
from po in participantsGroup
join winners in db.Winners on p.id
equals winners.participantId into winnersGroup
from w in winnersGroup
where p.hasAttended == 1 && p.weeknumber == weeknumber
select new
{
ParticipantId = p.id,
HasAttended = p.hasAttended,
Weeknumber = p.weeknumber,
UmbracoMemberId = p.umbMemberId,
Points = po.points,
HasWonFirstPrize = w.hasWonFirstPrize,
HasWonVoucher = w.hasWonVoucher
};
What I would like is to get some records even if the Winners table is empty or there is no match in it.
Any help/hint on this is greatly appreciated! :-)
Thanks a lot in advance.
/ Bo
If you set these up as related entities instead of doing joins, I think it will be easier to do what you're trying to do.
var query = from p in db.QuizParticipants
where p.hasAttended == 1 && p.weeknumber == weeknumber
select new
{
ParticipantId = p.id,
HasAttended = p.hasAttended,
Weeknumber = p.weeknumber,
UmbracoMemberId = p.umbMemberId,
Points = p.ParticipantPoints.Sum(pts => pts.points),
HasWonFirstPrize = p.Winners.Any(w => w.hasWonFirstPrize),
HasWonVoucher = p.Winners.Any(w => w.hasWonVoucher)
};
This is assuming hasWonFirstPrize and hasWonVoucher are boolean fields, but you can use any aggregate function to get the results you need, such as p.Winners.Any(w => w.hasWonFirstPrize == 1)
I don't use query syntax a lot but I believe you need to change from w in winnersGroup to from w in winnersGroup.DefaultIfEmpty()
I m trying to select a column's value from a datatable based on conditions.
var results = from DataRow myRow in dtCallBack.AsEnumerable()
where myRow.Field<DateTime>(1) == startDateTime
&& myRow.Field<int>(0) == callBackID
select myRow.Field<int>(3);
My datatable contains 4 columns ID,Date1,Date2,IntVal
I want to convert the variable results to int. (I want to return the column 4 IntVal)
var results = (from DataRow myRow in dtCallBack.AsEnumerable
where myRow.Field<DateTime>(1) == startDateTime
&& myRow.Field<int>(0) == callBackID
select myRow.Field<int>(3)).SingleOrDefault();
Well you've currently got an IEnumerable<int> by the looks of it. So which of those results do you want? What do you want to happen if there aren't any results?
If you're confident there's only a single result, you can use:
var result = results.Single();
If you want the first result or 0 if there aren't any, you could use
var result = results.FirstOrDefault();
If you want the first result and an exception if there aren't any, you could use
var result = results.First();
Basically there are lots of options, and you'll need to clarify your requirements before we can really give you a more concrete answer.