Question

IQueryable<Appeal> appeal = Repository.Appeals.Include("Case").Include("Case.Patient").Include("ShipmentAppeals").Where(ap => ap.CaseId == caseID);

IQueryable<ICollection<ShipmentAppeals>> shipmentAppeals = appeal.Select(ap => ap.ShipmentAppeals)

ShipmentAppeals是Appeal＆amp;的关联表。装运实体。

我想从Repository.Shipments中获取那些货件，其ShipmentID存在于以上的shipmentAppeals集合中。

我写的查询如下。它确实有效，但我想避免每个循环：

 foreach (ICollection<ShipmentAppeals> sAppealOuter in shipmentAppeals.ToList())
        {
            foreach (ShipmentAppeals sAppealInner in sAppealOuter)
            {
                Shipment shipment = Repository.Shipments.First(s => s.ID == sAppealInner.ShipmentID);
                    caseShipments.Add(shipment);
                }
            }

        }

Answer 1

首先，我们可以使用SelectMany将一系列上诉集合转换为上诉。

接下来，我们可以只使用一个查询来获取所有上诉的所有货件，而不是通过它们中的每一个并进行数据库查询以获得货件。这可以通过Join来完成。（或者，如果您不想要重复发货，可以使用GroupJoin并选择每个组中的第一个项目。）

var caseShipments = shipmentAppeals.SelectMany(repository => repository)
    .Join(Repository.Shipments, appeal => appeal.ShipmentID
        , shipment => shipment.ID, (appeal, shipment) => shipment);

或者在查询语法中：

var caseShipments = from repository in shipmentAppeals
                    from appeal in repository
                    join shipment in Repository.Shipments
                    on appeal.ShipmentID equals shipment.ID
                    select shipment;

请注意，由于延迟执行，此整个查询将只进行一次数据库往返，因为每个查询都用于组成另一个查询，而不是先执行。

Linq查询涉及关联表

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