Linq。使用LinqPad選擇方法問題

Question

我無法理解爲什麼在下面的代碼中出現錯誤。我確信我缺少一些簡單的東西，但我需要幫助理解。

我一直在使用LinqPad運行LinqToSql此代碼。

我在LinqPad以下代碼：

有三個表參與：出貨量，ShipmentDetails和ShipmentWeights。所有三個表都通過出貨單的PK來鏈接。

在這段代碼，最終查詢（「權重」）失敗，出現錯誤：「不支持例外：與當地館藏查詢不被支持。」我收集了LinqToSql中的某些東西不支持使用.Contains，但我不明白查詢名爲「Details」的查詢是如何工作的。這似乎是對我來說同樣的一種查詢。有人可以填補我的空白嗎？

對於那些誰不熟悉LinqPad中，使用.dump方法是IQueryable的只是一個擴展方法，打印出格式化的方式的內容。

var shipments = Shipments.Where(s => s.OrderID == "Some OrderID"); 
shipments.Dump("Shipments"); 

var shipmentIds = shipments.Select(s => s.ShipmentID); 
shipmentIds.Dump(); 

    //This query works. What is different about this query than the one that fails? 
var shipmentDetails = ShipmentDetails.Where(d => shipmentIds.Contains(d.ShipmentID)); 
shipmentDetails.Dump("Details"); 

var detailShipmentIds = shipmentDetails.Select(sd => sd.ShipmentID); 
detailShipmentIds.Dump(); 

//This is the query that generates the error 
    var shipmentWeights = ShipmentWeights.Where(w => detailShipmentIds.Contains(w.ShipmentID)); 
shipmentWeights.Dump("Weights"); 

Answer 1

你的列表是IQueryable的公司 - 即查詢沒有被執行又那麼它們不能被用作Contains查詢的一部分。只需將它們首先更改爲本地列表，然後這將工作。例如

var shipmentIds = shipments.Select(s => s.ShipmentID).ToList(); 

對所有本地列表都做同樣的事情。

這裏有一個完整列表

var shipments = Shipments.Where(s => s.OrderID == "Some OrderID"); 
shipments.Dump("Shipments"); 

var shipmentIds = shipments.Select(s => s.ShipmentID).ToList(); 
shipmentIds.Dump(); 

//This query works. What is different about this query than the one that fails? 
var shipmentDetails = ShipmentDetails.Where(d => shipmentIds.Contains(d.ShipmentID)); 
shipmentDetails.Dump("Details"); 

var detailShipmentIds = shipmentDetails.Select(sd => sd.ShipmentID).ToList(); 
detailShipmentIds.Dump(); 

//This is the query that generates the error 
var shipmentWeights = ShipmentWeights.Where(w => detailShipmentIds.Contains(w.ShipmentID)); 
shipmentWeights.Dump("Weights"); 

Answer 2

呀如指出的那樣，你將不得不做

var shipments = Shipments.Where(s => s.OrderID == "Some OrderID"); 
shipments.Dump("Shipments"); 

var shipmentIds = shipments.Select(s => s.ShipmentID).ToList(); 
shipmentIds.Dump(); 

    //This query works. What is different about this query than the one that fails? 
var shipmentDetails = ShipmentDetails.Where(d => shipmentIds.Contains(d.ShipmentID)); 
shipmentDetails.Dump("Details"); 

var detailShipmentIds = shipmentDetails.Select(sd => sd.ShipmentID).ToList(); 
detailShipmentIds.Dump(); 

//This is the query that generates the error 
    var shipmentWeights = ShipmentWeights.Where(w => detailShipmentIds.Contains(w.ShipmentID)); 
shipmentWeights.Dump("Weights");