EntityFramework 6 AddOrUpdate 不适用于复合或复合主键

使用EntityFramework 6的AddOrUpdate方法来插入或更新数据是非常方便的，但是它有一个限制，即不适用于复合或复合主键。在本文中，我们将探讨这个问题，并提供一些替代方案来解决这个问题。

csharp
// 定义一个包含复合主键的实体类
public class Employee
{
    [Key, Column(Order = 0)]
    public int DepartmentId { get; set; }
    
    [Key, Column(Order = 1)]
    public int EmployeeId { get; set; }
    
    public string Name { get; set; }
}
// 自定义的逻辑来处理复合主键的插入和更新
public static void AddOrUpdateEmployee(Employee employee)
{
    using (var context = new MyDbContext())
    {
        var existingEmployee = context.Employees.FirstOrDefault(e => e.DepartmentId == employee.DepartmentId && e.EmployeeId == employee.EmployeeId);
        
        if (existingEmployee != null)
        {
            existingEmployee.Name = employee.Name;
        }
        else
        {
            context.Employees.Add(employee);
        }
        
        context.SaveChanges();
    }
}
// 调用自定义的方法来插入或更新数据
var employee = new Employee
{
    DepartmentId = 1,
    EmployeeId = 1,
    Name = "John Doe"
};
AddOrUpdateEmployee(employee);