Linq to Entities Does Not Recognize the Method 'System.Web.Mvc.Fileresult'

LINQ to Entities does not recognize the method 'System.Object InjectFrom(System.Object, System.Object[])'

For the second version you will have to call AsEnumerable() inside your Select to tell clr that the method InjectFrom will be executed in memory.

return profileEntities.Select(x => (ProfileDTO)new ProfileDTO()
    {
      Localizations = _repoProfileLocalization
                          .Query(y => y.ProfileId == x.Id)
                          .AsEnumerable()
                          .Select(y => (ProfileLocalizationDTO)new ProfileLocalizationDTO()
                                      .InjectFrom(y))
                          .ToList()
    }
    .InjectFrom(x)).ToList();

In your first example because you instantiate a generic List inside the select, you will have all the results in memory after the select, because Linq can't execute that on the database. In the second example, Linq is still trying to do everything on the database in the select, but then you call a method which can't be translated to sql and you get the error.

LINQ to Entities does not recognize the method ToDateTime(System.String)

I Think I found the way to do it

var res =  db.Table1
//other tables, and where conditions
.Select(x => new MyObj
{
      //...
      Imp = x.MyTable.FirstOrDefault(y => y.date_val >= System.Data.Entity.DbFunctions.AddMonths(System.Data.Entity.DbFunctions.CreateDateTime(x.year, x.month, 1, 0, 0, 0), 1)).Description
})

LINQ to Entities does not recognize the method 'Boolean ToBoolean

What you are asking for cannot be achieved by db query. I'm afraid you are stuck with in memory filtering (hope your don't have too many records) like this

return 
_menuSettings.AsEnumerable().Where(...

here AsEnumerable() will switch the context from Linq to Entities to Linq to Objects

LINQ To Entities does not recognize the method Last. Really?

That limitation comes down to the fact that eventually it has to translate that query to SQL and SQL has a SELECT TOP (in T-SQL) but not a SELECT BOTTOM (no such thing).

There is an easy way around it though, just order descending and then do a First(), which is what you did.

EDIT:
Other providers will possibly have different implementations of SELECT TOP 1, on Oracle it would probably be something more like WHERE ROWNUM = 1

EDIT:

Another less efficient alternative - I DO NOT recommend this! - is to call .ToList() on your data before .Last(), which will immediately execute the LINQ To Entities Expression that has been built up to that point, and then your .Last() will work, because at that point the .Last() is effectively executed in the context of a LINQ to Objects Expression instead. (And as you pointed out, it could bring back thousands of records and waste loads of CPU materialising objects that will never get used)

Again, I would not recommend doing this second, but it does help illustrate the difference between where and when the LINQ expression is executed.

LINQ doesn't accept static function in a predicate: LINQ to Entities does not recognize the method

Perhaps using SqlFunctions.DatePart and ISO_WEEK will help

using (var ctx = new SchedulingToolContext())
{
    float qteSem = ctx.Reservations.Where(k => k.CltNameAlpha == item.CltNameAlpha
                        && k.DateReservation.Year == item.DateReservation.Year
                        && SqlFunctions.DatePart("isowk", this.DateReservation) ==  SqlFunction.DatePart("isowk", k.DateReservation) 
                        ).Sum(k => k.Qte);
                var q = ctx.Quotas.Where(k => k.Id == item.IdQuota).FirstOrDefault();
                return q.QteMaxJour >= item.Qte && q.QteMaxSemaine >= qteSem;
}

Error while converting nullable datetime to string in LINQ asp.net MVC

The error is pretty indicative LINQ to Entities does not support the ToString method, you should compare your dates using another approach.



Based on your code I assume you are only interested in the date part of the DateTime for comparison so I suggest you to try DbFunctions.TruncateTime Method:

Where(f => DbFunctions.TruncateTime(f.TimeStamp) == DbFunctions.TruncateTime(_temp))

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