一個在許多（IQueryable的）許多和搜索（LINQ）

Question

我有這樣的關係，在我的數據庫：

Order => historyStatus => Status 

Order包含HistoryStatus列表，並HistoryStatus包含一個Status。

我的使用情況是：搜索所有Order具有確定Status，並獲得最新HistoryStatus（根據日期）

我怎樣才能做到這在LINQ to實體和IQueryable？

這裏是實體：

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; } 
} 

這裏是我的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. 

感謝您的幫助:)

Answer 1

這將找到所有Orders其中對於最新HistoryStatusOrderOrder有一個特別的StatusOrderCode：

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

（假設每個Order總是有至少一個HistoryStatusOrder）

您可以用不同的方式編寫這個查詢保存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 
} 

如果你想繼續訪問LatestHistoryStatusOrder，您可以跳過最後的.Select(x => x.Order)聲明：

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 
}