LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression

Question

I\'m migrating some stuff from one mysql server to a sql server but i can\'t figure out how to make this code work:

using (var context = new Context())
{
            


        

Answer 1

I got the same error in this case:

var result = Db.SystemLog
.Where(log =>
    eventTypeValues.Contains(log.EventType)
    && (
        search.Contains(log.Id.ToString())
        || log.Message.Contains(search)
        || log.PayLoad.Contains(search)
        || log.Timestamp.ToString(CultureInfo.CurrentUICulture).Contains(search)
    )
)
.OrderByDescending(log => log.Id)
.Select(r => r);

After spending way too much time debugging, I figured out that error appeared in the logic expression.

The first line search.Contains(log.Id.ToString()) does work fine, but the last line that deals with a DateTime object made it fail miserably:

|| log.Timestamp.ToString(CultureInfo.CurrentUICulture).Contains(search)

Remove the problematic line and problem solved.

I do not fully understand why, but it seems as ToString() is a LINQ expression for strings, but not for Entities. LINQ for Entities deals with database queries like SQL, and SQL has no notion of ToString(). As such, we can not throw ToString() into a .Where() clause.

But how then does the first line work? Instead of ToString(), SQL have CAST and CONVERT, so my best guess so far is that linq for entities uses that in some simple cases. DateTime objects are not always found to be so simple...