LINQ：如何獲得兩組整數的交集？

Question

在使用LINQ時，必須有一種比較兩組結果的方法。 這是我現有的代碼，它使用HashSet在兩個單獨的查詢之后進行比較：

    public static void AssertDealershipsShareTransactionGatewayCredentialIds(long DealershipLocationId1,
        long DealershipLocationId2)
    {
        using (var sqlDatabase = new SqlDatabaseConnection())
        {
            var DealershipCredentials1 =
                sqlDatabase.Tables.DealershipLocationTransactionGateway
                    .Where(x => x.DealershipLocationId == DealershipLocationId1)
                    .Select(x => x.TransactionGatewayCredentialId);
            var DealershipCredentials2 =
                sqlDatabase.Tables.DealershipLocationTransactionGateway
                    .Where(x => x.DealershipLocationId == DealershipLocationId2)
                    .Select(x => x.TransactionGatewayCredentialId);
            var doSetsOfCredentialsMatch = new HashSet<int>(DealershipCredentials1).SetEquals(DealershipCredentials2);
            Assert.IsTrue(doSetsOfCredentialsMatch,
                "The sets of TransactionGatewayCredentialIds belonging to each Dealership did not match");
        }
    }

有想法嗎？ 謝謝。

Answer 1

簡單的答案（這將進行1個，可能是2個數據庫調用，兩個都只返回一個布爾值）：

if (list1.Except(list2).Any() || list2.Except(list1).Any()) 
{
   ... They did not match ...
}

更好的答案（這將使1個數據庫調用返回一個布爾值）：

var DealershipCredentials1 =
  sqlDatabase.Tables.DealershipLocationTransactionGateway
    .Where(x => x.DealershipLocationId == DealershipLocationId1)
    .Select(x => x.TransactionGatewayCredentialId);
var DealershipCredentials2 =
  sqlDatabase.Tables.DealershipLocationTransactionGateway
    .Where(x => x.DealershipLocationId == DealershipLocationId2)
    .Select(x => x.TransactionGatewayCredentialId);
if (DealershipCredentials1.GroupJoin(DealershipCredential2,a=>a,b=>b,(a,b)=>!b.Any())
    .Union(
      DealershipCredentials2.GroupJoin(DealershipCredential1,a=>a,b=>b,(a,b)=>!b.Any())
    ).Any(a=>a))
{
... They did not match ...
}

第二種方法通過合並左外部聯接來工作，該左外部聯接返回一個布爾值，該布爾值指示是否發現有不匹配記錄的右外部聯接執行相同的操作。 我沒有測試過，但是從理論上講，它應該從數據庫中返回一個簡單的布爾值。

另一種方法與第一種方法基本相同，但是包裝在單個LINQ中，因此它將始終僅進行1個數據庫調用：

if (list1.Except(list2).Union(list2.Except(list1)).Any())
{
}

還有另一種方法：

var common=list1.Intersect(list2);
if (list1.Except(common).Union(list2.Except(common)).Any()) {}