Comparing GUID to string in LINQ to Entites throws error [duplicate]

问题

EDIT, this is not a duplicate. The suggested SO links want me to call ToString() but I am running a .COUNT() and trying to do a greater than comparison so calling ToString() is not a correct answer.

I am trying to fill a variable using the IF shortcut but when I run it I get the error

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

The code I am running is

IsAdmin = (db.yaf_prov_RoleMembership
             .Where(rm => rm.UserID == UserKey
                          && rm.RoleID == Guid.Parse("adsfasd654asdf816asdf"))
             .Count() > 0) ? true : false;

If I take away the Guid.Parse and do a straight up comparison then I get the error

Operator == cannot be applied to operands of type System.Guid and String

What needs to be done in order to compare a GUID to a string in a LINQ query?

回答1:

Don't know why Dave deleted his answer - you should just move string parsing out of store expression. Otherwise Entity Framework tries to convert Guid.Parse method call to SQL, and fails to do that:

var adminRoleID = Guid.Parse("adsfasd654asdf816asdf");

Also use Queryable.Any to simplify your query:

IsAdmin = db.yaf_prov_RoleMembership
            .Any(rm => rm.UserID == UserKey && rm.RoleID == adminRoleID);

回答2:

The key part of your first error reponse is this: [...]into a store expression. If you parse the guid first and store in a var, I think it should work:

 var guid = Guid.Parse("adsfasd654asdf816asdf");
 IsAdmin = db.yaf_prov_RoleMembership
             .Any(rm => rm.UserID == UserKey && rm.RoleID == guid );

Whenever you do operations that the 'thing' that executes your LINQ queries does not know how to handle, you'll get this error. In this case, it's entity framework not knowing how to translate Guid.Parse into an SQL statement/ 'store expression'.

EDIT: Modified to use .Any. as per Sergey Berezovskiy's answer

来源：https://stackoverflow.com/questions/25354121/comparing-guid-to-string-in-linq-to-entites-throws-error

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linq