Update two relationship tables using Entity Framework

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entity-framework

Hi Friends,

Customer
{
customerid integer,
userid integer,
DOB timestamp
}

User
{
userid integer,
username varchar(100),
password varchar(100),
firstname varchar(50),
lastname varchar(50),
email varchar(100),
isactive bit
}

For username and password are updated on new mode.

The following statement to used to update on edit mode, but i am getting exception

First Way,

Customer editCustomer = DB.Customers.First(c => c.customerid == customerId);
if (editCustomer != null)
{
	User editUser = DB.Users.First(u => u.userid == editCustomer.User.userid);
	if (editUser != null)
	{
		editUser.firstname = userData.firstname;
		editUser.lastname = userData.lastname;
		editUser.email = userData.email;
		editUser.isactive = userData.isactive;
	}
	customerData.User = editUser;
	customerData.DOB = <input date>;
	editCustomer = customerData;
	DB.SaveChanges();
}

Second Way,

Customer editCustomer = DB.Customers.Include("User").Where(c => c.CustomerID == customerId).First();
if (editCustomer != null)
{
	editCustomer.User.FirstName = userData.FirstName;
	editCustomer.User.LastName = userData.LastName;
	editCustomer.User.Email = userData.Email;
	editCustomer.User.IsActive = userData.IsActive;
	DB.SaveChanges();
}

When i use second way the following exception shows,
"Entities in 'xxx.Customers' participate in the 'FK_Customer_User' relationship. 0 related 'User' were found. 1 'User' is expected."



What i did the mistake this execution?