如何使用 Entity Framework 在 2 个或更多表的连接视图上保存更改？

Question

为了练习使用实体框架，我正在创建一个 C# WinForms 项目，并使用此链接中问题的答案在 datagridview 中加入和显示表格：

Two entities in one dataGridView

我已经寻找一种干净的方法来保存（到 SQL Server 数据库）在 datagridview 中所做的更改。有没有好的、快速、简短、干净的方法？我见过一些丑陋的尝试，即使它们奏效了，我也被它们的丑陋吓倒了。

只有一张表（没有连接），调用 .SaveChanges 工作正常。

这是为保存连接字段而设置的类：

public class CustAndOrders
{
    // Customer table
    public Int64 Cust_Id { get; set; }
    public string Cust_Name { get; set; }
    public DateTime Cust_BDay { get; set; }

    //Order table
    public Int64 Order_Id { get; set; }
    public decimal Order_Amt { get; set; }
    public DateTime Order_Date { get; set; }

    // OrderDetail table
    public Int64 Item_Number { get; set; }
    public decimal Item_Amt { get; set; }
}

这是在 datagridview 中显示连接信息的代码。显然，SaveChanges 调用不起作用......但是

  AWModel.TestJLEntities dc;

    private void button1_Click(object sender, EventArgs e)
    {
        dc = new AWModel.TestJLEntities();

        var query = from c in dc.Customers
                    join o in dc.Orders on c.CustId equals o.CustId
                    join od in dc.OrderDetails on o.OrderId equals od.OrderId
                    orderby o.OrderDate ascending, c.CustId, o.OrderAmount
                    select new CustAndOrders
                    {
                        Cust_Id = c.CustId,
                        Cust_Name = c.CustName,
                        Cust_BDay = c.CustBday,
                        Order_Id = o.OrderId,
                        Order_Amt = o.OrderAmount,
                        Order_Date = o.OrderDate,
                        Item_Number = od.ItemNumber,
                        Item_Amt = od.ItemAmount
                    };
        var users = query.ToList();
        dataGridView1.DataSource = users;
    }

    private void button2_Click(object sender, EventArgs e)
    {
        try
        {
            dc.SaveChanges();
        }
        catch
        {
            MessageBox.Show("Error saving changes");
        }
    }

Answer 1

EF 看不到您的更改，因为您的数据网格视图未绑定到 EF 实体，而是从其实体填充的对象：

select new CustAndOrders
    {
        Cust_Id = c.CustId,
        Cust_Name = c.CustName,
        Cust_BDay = c.CustBday,
        Order_Id = o.OrderId,
        Order_Amt = o.OrderAmount,
        Order_Date = o.OrderDate,
        Item_Number = od.ItemNumber,
        Item_Amt = od.ItemAmount
    };

我能想到的一个解决方案是组合实体本身的 CustAndOrders：

public class CustAndOrders
{
    public Customer Customer { get; set; }
    public Order Order { get; set; }
    public OrderDetail OrderDetail { get; set; }
}

然后绑定到这些字段，即

{Binding Customer.CustId}

或者，如果您不想更改绑定，则将 EF 实体传递给 CustAndOrders 对象，然后在您的属性中从实体获取和设置：

public class CustAndOrders
{
    public Customer Customer { get; set; }
    public Order Order { get; set; }
    public OrderDetail OrderDetail { get; set; }

    // Customer table
    public Int64 Cust_Id
    {
        get
        { return Customer.CustId;}
        set
        { Customer.CustId = value; }
    }
... Do this for the rest of your properties

然后查询看起来像这样：

var query = from c in dc.Customers
                join o in dc.Orders on c.CustId equals o.CustId
                join od in dc.OrderDetails on o.OrderId equals od.OrderId
                orderby o.OrderDate ascending, c.CustId, o.OrderAmount
                select new CustAndOrders { Customer = c, Order = o, OrderDetail = od };