一个在许多（IQueryable的）许多和搜索（LINQ）

Question

我有这样的关系，在我的数据库：

Order => historyStatus => Status 

Order包含HistoryStatus列表，并HistoryStatus包含一个Status。

我的使用情况是：搜索所有Order具有确定Status，并获得最新HistoryStatus（根据日期）

我怎样才能做到这在LINQ to实体和IQueryable？

这里是实体：

public class Order 
{ 
    public int ID { get; set; } 

    public virtual ICollection<HistoryStatusOrder> HistoriesStatusOrder { get; set; } 
} 

public class HistoryStatusOrder 
{ 
    public int ID { get; set; } 
    public DateTime Date { get; set; } 
    public string StatusOrderCode { get; 
    public int OrderId { get; set; } 

    public virtual StatusOrder StatusOrder { get; set; } 
    public virtual Order Order { get; set; } 
} 

public class StatusOrder : IEntityBase<string> 
{ 
    public string ID { get; set; } 

    public virtual ICollection<HistoryStatusOrder> HistoriesStatusOrder { get; set; } 
} 

这里是我的Search方法：

// do multiple searches 
if (searchOrderVM.OrderNumber != null) 
    queryable = queryable.Where(x => x.OrderNumber.ToString().Contains(searchOrderVM.OrderNumber.ToString())); 

// Next 
if (searchOrderVM.SelectedOrdersStatus != null) 
{ 
    // Need to return queryable = .... 
} 

// Next search... 
.... 

// Finally I do .ToList() to launch the query in database. 

感谢您的帮助:)

Answer 1

这将找到所有Orders其中对于最新HistoryStatusOrderOrder有一个特别的StatusOrderCode：

var results = orders.Where (o => o.HistoriesStatusOrder 
    .OrderByDescending (hso => hso.Date) 
    .First().StatusOrderCode == "foobar"); 

（假设每个Order总是有至少一个HistoryStatusOrder）

您可以用不同的方式编写这个查询保存IQueryable<Order>：

var results = orders 
    .Select (o => new { 
     Order = o, 
     LatestHistoryStatusOrder = o.HistoriesStatusOrder 
      .OrderByDescending (hso => hso.Date) 
      .First() 
    }) 
    .Where (x => x.LatestHistoryStatusOrder.StatusOrderCode == "foobar") 
    .Select (x => x.Order); 

foreach(var order in results) 
{ 
    // Here you can access: 
    // order.ID 
} 

如果你想继续访问LatestHistoryStatusOrder，您可以跳过最后的.Select(x => x.Order)声明：

var results = orders 
    .Select (o => new { 
     Order = o, 
     LatestHistoryStatusOrder = o.HistoriesStatusOrder 
      .OrderByDescending (hso => hso.Date) 
      .First() 
    }) 
    .Where (x => x.LatestHistoryStatusOrder.StatusOrderCode == "foobar"); 

foreach(var item in results) 
{ 
    // Here you can access: 
    // item.Order.ID 
    // item.LatestHistoryStatusOrder 
}