Entity Framework: 'The SqlParameter is already contained by another SqlParameterCollection'

You just need to add ToList() method after the Sql query and remove @ in SqlParameter:

var result = userDbContext.users.SqlQuery("SELECT * FROM USERS WHERE 
@email=@emailValue",
new SqlParameter("email", "email"),
new SqlParameter("emailValue","[email protected]")).ToList();
//new SqlParameter("p1", existingUser.password));

if (result.Count() == 0) //getting exception here
{
    ViewBag.comment = "Sorry. We can not find your credentials";
    return View();
}

It will work.

do something like this:

SqlParameter parameter = new SqlParameter("email", SqlDbType.VarChar);
parameter.Value = "[email protected]";

or try like this:

var check =userDbContext.Database
           .SqlQuery<user>("SELECT * FROM USERS 
                           WHERE email=@emailValue", 
                           new SqlParameter("@emailValue","[email protected]")).ToList();

SqlParameter is like this:

var p = new SqlParameter {
    ParameterName = "paramName",
    DbType = DbType.Bit,
    Direction = ParameterDirection.Output
};

When you are using params by query, you can't use them by another query. In your code you are using them twice

1- userDbContext.users.SqlQuery....
2- result.Count().

but if you use this code:

"userDbContext.users.SqlQuery(...).Count()" 

your Code will be Correct

** SqlQuery does not return a query result until you use a linq extension like any(), tolist()..... on the other hand when you use SqlQuery, the result is an IEnumerable when you use any(), tolist(), first() it's converted to a result