I have a users table:
Users:
+ID
+Username
+...
I want to use myDBContext.Users.Find(Username)
to fin a users.
in my current context I can not use his ID.
do i have to use a full LINQ query ? e.g.
var user = from users in myDBContext.Users.Find(Username)
where users.Username == username
select users
I have also tried to define the username as a primary key in my edmx but that resulted in the following error:
Properties referred by the Principal Role User must be exactly identical to the key of the EntityType CamelotShiftManagementModel.User referred to by the Principal Role in the relationship constraint for Relationship CamelotShiftManagementModel.AssociationUserFK1. Make sure all the key properties are specified in the Principal Role. C:\Code\CamelotShiftManagement\CamelotShiftManagement\Models\CamelotDB.edmx 278 11 CamelotShiftManagement
Try with,
User myUser = myDBContext.Users.SingleOrDefault(user => user.Username == username);
Use SingleOrDefault
insted of Single
. If user doesn't exist then Single
will throw an error. While SingleOrDefault
will return null
if user not found otherwise User
object will be return.
Selection Between SingleOrDefault
and FirstOrDefault
You can get the user object by using SingleOrDefault
and FirstOrDefault
but while selecting which method to use consider below points.
SingleOrDefault
as it will thrown an exception if there are more than one element available.FirstOrDefault
for better performance compare to SingleOrDefault
FirstOrDefault
FirstOrDefault
or First
used when we required single value (first) from the collection or database.Some other remarks
username
is primary key then I think there will be no much/no difference between SingleOrDefault
and FirstOrDefault
performance as primary key has index and search on index column will always be faster than normal column.Single
or SingleOrDefault
will generate a regular TSQL like "SELECT ...".First
or FirstOrDefault
method will generate the TSQL statment like "SELECT TOP 1..."I've found it:
User myUser = myDBContext.Users.Single(user => user.Username == i_Username);