I am new to LINQ and I am getting the following error when placing a method within the following Where clause:
LINQ to Entities does not recognize the method 'System.String getPrefixBySize(Int32, Int32, Int32, Int32)' method, and this method cannot be translated into a store expression.
adminGalleryDesignerVM.Thumbnails = (from tn in db.Media
from fd in db.FileDescendants
where tn.GalleryId == galleryId && fd.FileId == tn.FileId
&& fd.Prefix == FM.getPrefixBySize(fd.FileId, 250, 250, 1)
select new FileVM
{
id = tn.MediaId,
FileName = tn.File.FileName,
URL = FM.getMediaURL(tn.FileId, fd.Prefix),
Height = fd.FileHeight,
Width = fd.FileWidth
}).ToList();
Thanks!
LinqToEntities will try to convert ALL of the criteria in the query to SQL. Since it can't directly convert getPrefixBySize to SQL, the entire query fails.
You have a few options:
Get more data than you need to and filter more using Linq-to-Objects:
adminGalleryDesignerVM.Thumbnails = (
from tn in db.Media
from fd in db.FileDescendants
where tn.GalleryId == galleryId && fd.FileId == tn.FileId
select new
{
id = tn.MediaId,
FileName = tn.File.FileName,
tn.FileId,
fd.Prefix,
Height = fd.FileHeight,
Width = fd.FileWidth
})
.AsEnumerable() // hydrate the query
.Where(x => x.Prefix == FM.getPrefixBySize(x.FileId, 250, 250, 1)
.Select(x => new FileVM
{
id = x.id,
FileName = x.FileName,
URL = FM.getMediaURL(x.FileId, x.Prefix),
Height = x.Height,
Width = x.Width
})
.ToList();
Replace the call to getPrefixBySize with inline functions that can be converted to SQL (if possible) such as basic value comparisons, etc.
Related
I have a linq query like this :
var trfplanList = (from at in entities.tdp_ProviderAccomodationType
join ap in entities.tdp_ProviderAccomodationTariffPlan on at.PATID equals ap.FK_PATID
join ac in entities.tdp_ProviderAccomodationCategory on ap.FK_PACID equals ac.PACID
where at.FK_ProviderID == CityID && at.IsApproved == 0 && ap.IsApproved == 0 && ac.AccomodationCategory == "Double Occupy"
orderby at.AccomodationType,ap.FromDate,ap.SType
select new AccomodationTariff
{
AccomodationType = at.AccomodationType,
SType = ap.SType,
FromDate = Convert.ToDateTime(ap.FromDate),
ToDate = Convert.ToDateTime(ap.ToDate),
RoomTariff = Convert.ToDecimal(ap.Rate),
ExPAXRate = Convert.ToDecimal(at.PerPaxRate)
}).ToList();
I have two questions:
Can't I convert value while assigning in the select new {} block ? it is giving me an error in project.
I want use 'case' while selecting ExPAXRate from the database for example in SQL I used to write :
CASE ap.SType WHEN 'Off Season' THEN at.PerPaxRateOS ELSE at.PerPaxRate END AS ExPAXRate
Can I use something like this in linq query ?
Can't I convert value while assigning in the select new {} block
No, you can't (sadly). EF doesn't know how to translate it into SQL.
I want use 'case'
You can use the ternary operator (?):
ExPAXRate = at.OffSeason ? at.PerPaxRateOS : at.PerPaxRate
(assuming that at.OffSeason exists).
A solution for the conversion issue could be to project into an anonymous type first and then, in memory, to AccomodationTariff:
...
select new
{
AccomodationType = at.AccomodationType,
SType = ap.SType,
FromDate = ap.FromDate,
ToDate = ap.ToDate,
RoomTariff = ap.Rate,
ExPAXRate = at.PerPaxRate
}).AsEnumerable()
.Select(x => new AccomodationTariff
{
AccomodationType = x.AccomodationType,
SType = x.SType,
FromDate = Convert.ToDateTime(x.FromDate),
ToDate = Convert.ToDateTime(x.ToDate),
RoomTariff = Convert.ToDecimal(x.Rate),
ExPAXRate = Convert.ToDecimal(x.PerPaxRate)
}).ToList();
Hi I have a linq query as below
var perChange = (from data in globalDS.Tables[0].AsEnumerable().AsParallel()
select data.Field<double>("PercentChange")).ToList();
Now the dataset globalDS contains null as well as varchar values in them. So there is an obvious type cast error that is generated. Is there a way to try.Parse the value in "Percentage Change" column and select only the valid fields.
DataRow.Field supports nullable types:
List<double> result = globalDS.Tables[0].AsEnumerable().AsParallel()
.Where(r => r.Field<double?>("PercentChange").HasValue)
.Select(r => r.Field<double?>("PercentChange").Value)
.ToList();
Edit: Since you have mentioned that the field contains strings instead of doubles:
List<double> result = globalDS.Tables[0].AsEnumerable().AsParallel()
.Select(r => r.Field<string>("PercentChange").TryGetDouble())
.Where(nullDouble => nullDouble.HasValue)
.Select(nullDouble => nullDouble.Value)
.ToList();
I've used this extension to try-parse a string to double? which is safer than parsing "on the fly" into the local variable, especially with AsParallel:
public static Double? TryGetDouble(this string item, IFormatProvider formatProvider = null)
{
if (formatProvider == null) formatProvider = NumberFormatInfo.CurrentInfo;
Double d = 0d;
bool success = Double.TryParse(item, NumberStyles.Any, formatProvider, out d);
if (success)
return d;
else
return null;
}
How about this:
double temp;
var perChange = (
from data in globalDS.Tables[0].AsEnumerable().AsParallel()
where !data.IsNull("PercentChange")
&& double.TryParse(data.Field<string>("PercentChange"), out temp)
select double.Parse(data.Field<string>("PercentChange"))
).ToList();
Try a select using a where clause in which you check the type. This would be something like: where x != null && TypeOf(x) == double
I need to return only the first record. Although I had to put the z.FirstOrDefault(); still more than one were displayed
public DataTable GetDependents(string EmployeeID)
{
HealthCareSystem.DataClassesDataContext db = new HealthCareSystem.DataClassesDataContext();
var z = (from s in db.SelectingDependentsGroupBies
where s.EmployeeID.Equals(EmployeeID)
join d in db.Dependents on s.DependentID equals d.DependentID
orderby s.DependentID descending
//Selecting wanted tables dependents fields by datatable
select new DependentsX { DependentID = Convert.ToInt32(s.DependentID), EmployeeID = s.EmployeeID, Name = s.Name, Surname = s.Surname, IDCardNo = s.IDCardNo, ContactNo = s.ContactNo, BirthDate = s.BirthDate, StartSchemeDate = s.StartDate, EndSchemeDate = s.EndDate, RelationType = s.Type, Payment = Convert.ToDouble(d.Payment), });
var firstRecord = z.FirstOrDefault();
Add this line after your existing code:
var firstRecord = x.First();
If there might be zero results and you don't want an exception then you can use FirstOrDefault instead.
var firstRecord = x.FirstOrDefault();
Another common way is to enclose your query in parenthesis and then include the extension methods outside the parenthesis:
var x = (from d in db.DependentsRelationsViews
where d.IDCardNo.Equals(DepID)
orderby d.DependentID descending
select new DependentsX
{
DependentID = Convert.ToInt32(d.DependentID),
EmployeeID = d.EmployeeID,
Name = d.Name,
Surname = d.Surname,
IDCardNo = d.IDCardNo,
ContactNo = d.ContactNo,
BirthDate = d.BirthDate,
StartSchemeDate = Convert.ToDateTime(d.StartSchemeDate),
EndSchemeDate = d.EndSchemeDate,
Payment = d.Payment,
RelationType = Convert.ToString(d.Type)
}).FirstOrDefault();
If you don't enclose it in parenthesis and try to call FirstOrDefault() then you're applying that extension to the anonymous type in just the very last Select clause. By enclosing the whole query in parenthesis and then calling the FirstOrDefault() extension, you're indicating to the compiler that you wish to apply it to the return value of your entire query, which will be the IEnumerable<> or IQueryable<> collection.
Is there a better way to check if a LINQ projection query returns results:
IList<T> TList = db.Ts.Where(x => x.TId == 1).ToList(); // More canonical way for this?
if (TitleList.Count > 0)
{
// Result returned non-zero list!
string s = TList.Name;
}
You can use Any(), or perhaps more appropriately to your example, SingleOrDefault(). Note that if you are expecting more than one result and plan to use all of them, then it doesn't really save anything to use Any() instead of converting to a List and checking the length. If you don't plan to use all the results or you're building a larger query that might change how the query is performed then it can be a reasonable alternative.
var item = db.Ts.SingleOrDefault( x => x.TId == 1 );
if (item != null)
{
string s = item.Name;
...
}
or
var query = db.Ts.Where( x => x.Prop == "foo" );
if (query.Any())
{
var moreComplexQuery = query.Join( db.Xs, t => t.TId, x => x.TId );
...
}
I have a LINQ query that looks like this...
var duration = Level3Data.AsQueryable().Sum(d => d.DurationMonths);
If all the d.DurationMonths values are null the Sum returns 0. How can I make the Sum return null if all the d.DurationMonths are null? Or do I need to run a separate query first to eliminate this situation before performing the sum?
Along with the previous suggestion for an extension method - you could use a ternary operator...
var duration = Level3Data.AsQueryable().Any(d => d.DurationMonths.HasValue)
? Level3Data.AsQueryable().Sum(d => d.DurationMonths)
: null;
You can use Aggregate to provide custom aggregation code :
var items = Level3Data.AsQueryable();
var duration = items.Aggregate<D,int?>(null, (s, d) => (s == null) ? d.DurationMonths : s + (d.DurationMonths ?? 0));
(assuming the items in Level3Data are of type D)
var outputIndicatorSum = (from OutputIndicatorTable in objDataBaseContext.Output_Indicators
where OutputIndicatorTable.Output_Id == outputId
select (int?)OutputIndicatorTable.Status).Sum();
int outputIndicatorSumReturn = Convert.ToInt32(outputIndicatorSum);
return outputIndicatorSumReturn;
You can explicitly type cast non-nullable varaible into nullable type.
i.e, select (int?)OutputIndicatorTable.Status).Sum();
Using Sum alone, this is impossible. As you indicated in your question, you will need to check for this situation before you call Sum:
var q = Level3Data.AsQueryable();
var duration = q.All(d => d.DurationMonths == null)
? null
: q.Sum(d => d.DurationMonths);
If you would like the result without two queries try:
var duration = Level3Data.AsQueryable().Sum(d => (double?)d.DurationMonths);
If you want zero instead of null as the result of this query use:
var duration = Level3Data.AsQueryable().Sum(d => (double?)d.DurationMonths) ?? 0;