linq exception : This function can only be invoked from LINQ to Entities

Question

I'm trying to get data which is kept on cache. But it throws an exception on "select new FilterSsrsLog" line. Exception: This function can only be invoked from LINQ to Entities ``` List reportServerDB = UpdateCache(); var reportLog = (from r in reportServerDB orderby r.TimeStart descending where ((model.reportName == null ? true : r.ItemPath.Contains(model.reportName)) && (model.reportFolder == null ? true : r.ItemPath.Contains(model.reportFolder)) && (r.TimeStart >= startDateTime) && (r.TimeStart <= endDateTime) ) select new FilterSsrsLog { UserName = r.UserName, ReportName = r.ItemPath, ReportFolder = r.ItemPath, Format = r.Format, Parameters = r.Parameters, TimeStart = r.TimeStart, TimeEnd = r.TimeEnd, TotalTime = EntityFunctions.DiffMilliseconds(r.TimeStart, r.TimeEnd) }); ``` If i remove "select new FilterSsrsLog" code block and write "select r" it works. But i need only that coloumns so what can i do to solve this problem?

Accepted Answer

The reason you are getting this error is that the query is executed in memory, not in RDBMS. The `DiffMilliseconds` function is a marker that Entity Framework provider converts to RDBMS-specific SQL to send to your RDBMS. The function does not compute its result when applied to an `IQueryable<T>` in memory, throwing an exception instead.

If you want to run this query in memory, replace

```
TotalTime = EntityFunctions.DiffMilliseconds(r.TimeStart, r.TimeEnd)
```

with

```
TotalTime = (r.TimeEnd - r.TimeStart).TotalMilliseconds
```

Subtraction of two dates produces a `TimeSpan` value from which you can take its `TotalMilliseconds` property.

linq exception : This function can only be invoked from LINQ to Entities

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