Issue with Linq lambda expression

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C#

LINQ

expression

lambda

ASP.NET4

I have some issues with Linq lambda expression.
I want to filter some User's data with it's related nested list objects.

Current Code

var aUser = (from u in db.Users
                             join c in db.UserContacts on u.UserId equals c.UserId
                             join a in db.AccountTypes on u.AccountTypeId equals a.AccountTypeId
                             join r in db.Roles on u.RoleId equals r.RoleId
                             where c.ContactTypeId == (int)Global.enContactType.Email 
                             select new { u.FirstName, u.LastName, u.DisplayName, u.Username, u.Status, u.UserId, Email = c.Description, AccountTypeName = a.Description, Role = r.Description });

if (strField == "Role")
    aUser = aUser.Where(x => x.Role.Contains(strName));
else if (strField == "DisplayName")
    aUser = aUser.Where(x => x.DisplayName.Contains(strName));
else if (strField == "AccountTypeName")
    aUser = aUser.Where(x => x.AccountTypeName.Contains(strName));
else if (strField == "Username")
    aUser = aUser.Where(x => x.Username.Contains(strName));
else if (strField == "Email")
    aUser = aUser.Where(x => x.Email.Contains(strName));
else if (strField == "Status")
{
    if ("true,1".Contains(strName.ToLower()))
        aUser = aUser.Where(x => x.Status == true);
    if ("false,0".Contains(strName.ToLower()))
        aUser = aUser.Where(x => x.Status == false);
}

But I want to do with Expression.

System.Linq.Expressions.Expression<Func<UserContact, bool>> objEmail = c => c.ContactTypeId == 1;
                System.Linq.Expressions.Expression<Func<User, bool>> objTest = p => p.UserContacts.Where(objEmail).ToList();



                if (strField == "Role")
                    objTest = p => p.Role.Description.Contains(strName);
                else if (strField == "DisplayName")
                    objTest = p => p.DisplayName.Contains(strName);
                else if (strField == "AccountTypeName")
                    objTest = p => p.AccountType.Description.Contains(strName);
                else if (strField == "Username")
                    objTest = p => p.Username.Contains(strName);
                else if (strField == "Email")
                    objTest = p => p.UserContacts.SingleOrDefault().Description.Contains(strName);

                IQueryable<User> iUser =(IQueryable<User>) db.Users.ToList();

                iUser = iUser.Where(objTest);

Below is my User Model Class:

public virtual AccountType AccountType { get; set; }
public virtual Currency Currency { get; set; }
public virtual Role Role { get; set; }
public virtual ICollection<UserAddress> UserAddresses { get; set; }
public virtual ICollection<UserContact> UserContacts { get; set; }
public virtual ICollection<UserImage> UserImages { get; set; }
public virtual ICollection<UserMessage> UserMessages { get; set; }
public virtual ICollection<UserMessage> UserMessages1 { get; set; }
public virtual ICollection<CourerCompanyTrailer> CourerCompanyTrailers { get; set; }
public virtual ICollection<CourerCompanyTrailer> CourerCompanyTrailers1 { get; set; }
public virtual ICollection<CourierCompanyServiceCategory> CourierCompanyServiceCategories { get; set; }
public virtual ICollection<Vehicle> Vehicles { get; set; }

I want to filter UserContact with it's ContactTypeId = 1

Thanks for advance.