C# 代码首先添加具有多对多关系的实体

我有一个对象客户，可以有多个客户类型，每个客户类型可以有多个客户。我是EF的新手，但已经成功添加了一个客户，但似乎无法获得添加客户的客户类型的正确语法

我的客户类别（简化）：

我在这里查看了一下，并尝试对客户类型执行类似的操作：

var customer = new Customer();
customer.name = txtCustomerName.Text;

// only starting with one customer type selected in a check box list
CustomerType customerType = context.CustomerTypes.FirstOrDefault(i => i.Id == 1);

using (var context = new MyEntities())
{
    // IncidentTypes throws Object reference not set to an instance of an object
    customer.CustomerTypes.add(customerType);

    context.Customers.Add(customer);
    context.SaveChanges();  
}

我是不是漏掉了什么明显的东西

提前谢谢

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编辑：由于某些原因，我只有.Add（无AddToObject、AttachTo等）

您必须首先初始化

CustomerType

集合

customer.CustomerTypes = new List<CustomerType>();

customer.CustomerTypes=新列表（）；

---

您还可以将此初始化添加到

客户的构造函数中。
这是一种方法：

var customer = new Customer();
customer.name = txtCustomerName.Text;

// only starting with one customer type selected in a check box list
//add Include there
CustomerType customerType = context.CustomerTypes.Include("Customers").FirstOrDefault(i => i.Id == 1);

using (var context = new MyEntities())
{
    // IncidentTypes throws Object reference not set to an instance of an object
    //customer.CustomerTypes.add(customerType);

    //context.Customers.Add(customer);
    customerType.Customers.Add(customer);
    context.SaveChanges();  
}

var customer = new Customer();
customer.name = txtCustomerName.Text;

// only starting with one customer type selected in a check box list
CustomerType customerType = context.CustomerTypes.FirstOrDefault(i => i.Id == 1);

using (var context = new MyEntities())
{
    // IncidentTypes throws Object reference not set to an instance of an object
    customer.CustomerTypes.add(customerType);

    context.Customers.Add(customer);
    context.SaveChanges();  
}

customer.CustomerTypes = new List<CustomerType>();

var customer = new Customer();
customer.name = txtCustomerName.Text;

// only starting with one customer type selected in a check box list
//add Include there
CustomerType customerType = context.CustomerTypes.Include("Customers").FirstOrDefault(i => i.Id == 1);

using (var context = new MyEntities())
{
    // IncidentTypes throws Object reference not set to an instance of an object
    //customer.CustomerTypes.add(customerType);

    //context.Customers.Add(customer);
    customerType.Customers.Add(customer);
    context.SaveChanges();  
}