如何将具有一对多相关数据的SQL Server视图映射到ASP.NET Core 2.2中具有ICollection的ViewModel类

Question

我想创建一个如下所示的视图模型，其中CustomerInfo是包含订单集合的视图模型，每个订单都包含订单明细的集合。

 public class CustomerInfo
 {
     public CustomerInfo()
     {
         OrderInfo = new HashSet<OrderInfo>();
     }

     public int Custid { get; set; }
     public string City { get; set; }
     public string Region { get; set; }

     public virtual ICollection<OrderInfo> OrderInfo { get; set; }
 }

 public class OrderInfo
 {
     public OrderInfo()
     {
         OrderDetails = new HashSet<OrdDetails>():
     }

     public int OrderId { get; set; }
     public DateTime OrderDate { get; set; }

     public ICollection<OrdDetails> OrderDetails { get; set; }
 }

 public class OrdDetails
 {
     public int Orderid { get; set; }
     public int Productid { get; set; }
     public decimal Unitprice { get; set; }
     public short Qty { get; set; }
     public decimal Discount { get; set; }

     public virtual OrderInfo Order { get; set; }
 }

SQL Server数据库包含一个视图，该视图使用联接存储来自三个相关表：customer，order和orderdetails的数据。

我是否可以使用无键实体类型或DBQuery将T-SQL视图映射到CustomerInfo视图模型类？

如果可能，我宁愿不使用DBQuery，因为最新的.NET Core版本不再支持DBQuery，并且如果我们决定升级，我不希望该应用程序损坏。

Answer 1

这不是一件容易的事。

假设有一个实体类，声明为数据库记录包含复合Customer，Order和OrdDetail关系主列，

public partial class CustomerOrderDetail_Entity : ICustomerInfo, IOrderInfo, IOrdDetails
{
    public int Custid { get; set; }
    public string City { get; set; }
    public string Region { get; set; }
    public int OrderId { get; set; }
    public DateTime OrderDate { get; set; }
    public int Orderid { get; set; }
    public int Productid { get; set; }
    public decimal Unitprice { get; set; }
    public short Qty { get; set; }
    public decimal Discount { get; set; }
}

为了使开始时变得容易和简单，请尝试创建视图并查询这三个表中的每一列，

SELECT  
  dbo.Customer.Custid, dbo.Customer.City, dbo.Customer.Region, 
  dbo.[Order].OrderId, dbo.[Order].OrderDate, 
  dbo.OrdDetail.Productid, dbo.OrdDetail.Qty, dbo.OrdDetail.Discount, dbo.OrdDetail.Unitprice
FROM  dbo.Customer LEFT OUTER JOIN
  dbo.[Order] ON dbo.Customer.Custid = dbo.[Order].Custid LEFT OUTER JOIN
  dbo.OrdDetail ON dbo.[Order].OrderId = dbo.OrdDetail.Orderid

然后，创建数据访问，ORM功能来满足您的需求，

virtual CustomerInfo GetCustomerOrderDetail(int custId, string connectionStringName = null)
{
    IEnumerable<CustomerOrderDetail_Entity> entities;
    using (var conn = DbConnectionFactory.CreateDbConnection(connectionStringName ?? DefaultConnectionName))
    {
        conn.Open();
        entities = conn.Query<CustomerOrderDetail_Entity>(@"
SELECT *
FROM uv_CustomerOrderDetails
where CustId = @CustId
", new { CustId = custId });
    }

    return entities?.ConvertTo<CustomerInfo>(); 
}

无论您的数据结构多么复杂，它都是ORM映射的东西。由于现在所有事物都在内存中，因此使用OrdDetails将它们转换或映射为OrderInfo，CustomerInfo和legacy for-loop, LINQ, or 3rd-party mapper package类可能并不困难。

---

但是，不应为一般目的而创建第一个视图，对于不经常调用的查询，例如数据分析，这是更好的选择，否则它会不断浪费大量流量来检索带有冗余列的较大数据集，例如[ C0]，Customer.City，对于客户而言，它们都是相同的，对于相同的订单，它们也都是Customer.Region。

[像这样，比伯爵眼镜还相对优化的视图，

[Order].OrderDate
尽管现在节省了大量数据，但CustomerOrderDetail_Entity

数据不再完全填充。相反，需要许多支持方法来使其完成。这是一个示例，我如何使用第二个视图，然后将数据集分别转换为

SELECT  
  dbo.Customer.Custid, 
  dbo.[Order].OrderId, 
  dbo.OrdDetail.Productid
FROM  dbo.Customer LEFT OUTER JOIN
  dbo.[Order] ON dbo.Customer.Custid = dbo.[Order].Custid LEFT OUTER JOIN
  dbo.OrdDetail ON dbo.[Order].OrderId = dbo.OrdDetail.Orderid

，CustomerInfo和OrderInfo。

OrdDetails
坦率地说，随着系统复杂性的增加，还有很多事情要做。除非您的系统保持如此小，我的意见是virtual CustomerInfo GetCustomerOrderDetail(int custId, string connectionStringName = null)
{
    var customerInfo = DBHelper.CachedCustomerInfo(custId);
    var orders = entities
        ?.Where(o => o.Custid == custId)
        ?.GroupBy(o => o.Custid)
        ?.SelectMany(group => group);
    if (orders?.Count() > 0 != true)
    {
        return customerInfo;
    }

    customerInfo.OrderInfo = new List<OrderInfo>();

    // fill orders
    foreach (var order in orders)
    {
        var orderId = order.OrderId;
        if (orderId <= 0)
        {
            continue;
        }

        var orderInfo = DBHelper.CachedOrderInfo(orderId);
        customerInfo.OrderInfo.Add(orderInfo);

        // fill order details
        var orderDetails = DBHelper.CachedOrderDetails(orderId);
        if (orderDetails?.Count() > 0 != true)
        {
            continue;
        }

        orderInfo.OrderDetails = orderDetails.LinkOrder(orderInfo).ToList();
    }

    return customerInfo;
}

// query CustomerInfo by PK:CustId, and Cache CRUD
virtual CustomerInfo CachedCustomerInfo(int custId);

// query OrderInfo by PK:OrderId, and Cache CRUD
virtual OrderInfo CachedOrderInfo(int orderId);

// query OrdDetails list by FK:OrderId, and Cache CRUD
virtual IEnumerable<OrdDetails> CachedOrderDetails(int orderId);

// make OrdDetails.Order property link to its owner Order
virtual IEnumerable<OrdDetails> LinkOrder(this IEnumerable<OrdDetails> details, OrderInfo order);
。