Linq to Entities group by week number

Question

I am using ASP.NET v4.5 and linq to entities I am trying to group my data by week using the below code ``` var groupedByWeek = salesOrdersList .GroupBy(i => i.DueDate.AddDays(-(int)i.DueDate.DayOfWeek)); ``` However I am getting a "yellow screen of death" with the error: LINQ to Entities does not recognize the method 'System.DateTime AddDays(Double)' method, and this method cannot be translated into a store expression. Ideally I would like to put ``` var groupedByWeek = salesOrdersList.GroupBy(i => i.DueDate.WeekNumber); ``` But life isn't that easy! Does anyone know a way of using week numbers with Linq to Entities?

Accepted Answer

Use `SqlFunctions.DatePart()` method:

```
var groupedByWeek = salesOrdersList.GroupBy(i => SqlFunctions.DatePart("week", i.DueDate));
```

It will add `DATEPART` sql function call into generated SQL query.

Linq to Entities group by week number

Solution

Problem