c# - 如何在 LINQ to DB 模型类中添加表之间的关系

Question

我正在使用 LINQ to DB (linq2db)，我有一个类 Activity.cs，它有一个 Customer 属性，如下所示:

public Customer Customer { get; set; }

客户类:

    public class Customer
{
    [PrimaryKey, Identity]
    [Column(Name = "CustomerId"), NotNull]
    public string Id { get; set; }

    [Column(Name = "Name")]
    public string Name { get; set; }
}

现在，我希望能够做这样的事情:

db.Activities.First().Customer.Name  //Returns the customer name of an activity

如何设置实体之间的关系，以便我可以像上面解释的那样做？

(是的，我知道将 Id 字段作为字符串没有意义，我必须处理困惑的遗留 Access 数据库)

Answer 1

如果我很好理解，一个Activity 有一个Customer。如果是这样，您应该向您的 Activity 类添加一个关系:

[Table( Name = "Customers" )]
public class Customer
{
    [PrimaryKey, Identity]
    [Column(Name = "CustomerId"), NotNull]
    public string Id { get; set; }

    [Column(Name = "Name")]
    public string Name { get; set; }
}

[Table( Name = "Activities" )]
public class Activity
{
    [PrimaryKey, Identity]
    [Column(Name = "ActivityId"), NotNull]
    public string Id { get; set; }

    [Column( Name = "Customer" )] 
    private int? customerId; 

    private EntityRef<Customer> _customer = new EntityRef<Customer>( );

    [Association(IsForeignKey = true, Storage = "_customer", ThisKey = "customerId" )]
    public Customer Customer{
        get { return _customer.Entity; }
        set { _customer.Entity = value; }
    }
}

A good article about this subject

编辑:

关联不起作用时的绕行:

[Table( Name = "Activities" )]
public class Activity
{
    [PrimaryKey, Identity]
    [Column(Name = "ActivityId"), NotNull]
    public string Id { get; set; }

    [Column( Name = "CustomerId" )] 
    public int? CustomerId; 

}

您可以像这样从事件中检索客户:

var activity = db.Activities.FirstOrDefault()
var customer = db.Customers.FirstOrDefault(c => c.Id = activity.CustomerId);