Question

我使用EF代码优先，我有这样的模型：

public class Product
{
    [Key]
    public int Id { get; set; }

    [Required]
    public string Name { get; set; }

    public Customer Customer { get; set; }
}

public class Customer 
{
    public Customer ()
    {
        Products = new List<Product>();
    }

    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int Id { get; set; }

    // more stuff snipped...

    public ICollection<Product> Products{ get; set; }
}

我正在收到客户ID以及产品ID列表。当产品在DB中不存在时，我想添加它：

    var newProduct = new Product{ Id = id, Name = "<no name yet>", Customer = customer };
    InsertProduct(newProduct);

问题是EF尝试级联更改并尝试插入一个新的Customer对象，其ID与现有对象相同，因此失败。我该如何解决这个问题？

这是插入方法：

    public void InsertProduct(Product item)
    {
        CustomerContext.Entry(item).State = EntityState.Added;
        CustomerContext.Set<Product>().Add(item);
    }

Answer 1

取自here.

添加具有现有子对象（数据库中存在的对象）的新实体时，如果EF未跟踪子对象，则将重新插入子对象。除非您先手动附加子对象。

尝试以下内容设置子对象状态：

public void InsertProduct(Product item)
{
    // Calling this code before the context is aware of the Child
    // objects will cause the context to attach the Child objects to the     
    // context and then set the state.
    // CustomerContext.Entry(childitem).State = EntityState.Unchanged
    CustomerContext.Entry(item.ChildObject).State = EntityState.Modified;

    CustomerContext.Entry(item).State = EntityState.Added;
    CustomerContext.Set<Product>().Add(item);
}

Answer 2

如果向父类添加外键，则更容易：

public class Product
{
    ....

    public int CustomerId { get; set; }

    public Customer Customer { get; set; }
}

然后，当您要插入时，设置外键而不是导航属性：

    var newProduct = new Product
       { 
          Id = id, 
          Name = "<no name yet>", 
          CustomerId = customer.Id 
       };
   InsertProduct(newProduct);

参考文献：

Why does Entity Framework Reinsert Existing Objects into My Database?

Making Do with Absent Foreign Keys

插入新实体而不创建子实体（如果存在）

2 个答案: