Question

我有一个客户，可以有多种客户类型，每种客户类型可以有多个客户。我是EF的新手，但已经设法添加了一个客户，但似乎无法正确添加客户的客户类型的语法。

我的客户类（简化）：

public partial class Customer
{
        public virtual int Id { get; set;}
        public virtual string Name { get; set;}

    #region Navigation Properties

        public virtual ICollection<CustomerType> CustomerTypes
        { get; set; }

    #endregion
}

客户类型：

public partial class CustomerType
{

        public virtual int Id
        {
            get;
            set;
        }

        public virtual string Name
        {
            get;
            set;
        }

        #region Navigation Properties

        public virtual ICollection<Customer> Customers
        { get; set; }

        #endregion
}

当我运行这个项目时，会创建一个CustomerTypeCustomer表，其中包含Customer_Id和CustomerType_Id列，所以这很好。

然后我就像这样创建客户：

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

using (var context = new MyEntities())
{   
    context.Customers.Add(customer);
    context.SaveChanges();  
}

我在这里查看了Insert/Update Many to Many Entity Framework . How do I do it?，并尝试与客户类型做类似的事情：

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();  
}

我错过了一些明显的东西吗？

提前致谢。

编辑：出于某种原因我只有.Add（没有AddToObject，AttachTo等。

Answer 1

您必须先初始化CustomersTypes集合。

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

您也可以将此初始化添加到Customer的构造函数中。

Answer 2

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();  
}

代码首先添加具有多对多关系的实体

2 个答案: