一对多和多搜索 (IQueryable) (linq)

Question

我的数据库中有这种关系：

Order => historyStatus => Status

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

我的用例是：用确定的Status 搜索所有Order 并获取最新的HistoryStatus（基于日期）

如何在 linq to entity 和 IQueryable 中做到这一点？

以下是实体：

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，其中最新的HistoryStatusOrder Order 具有特定的StatusOrderCode：

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

（假设每个Order 总是至少有一个HistoryStatusOrder）

您可以用不同的方式编写此查询来保留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
}

如果您想继续访问LatestHistoryStatusOrder，可以跳过最后的.Select(x => x.Order) 语句：

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
}