如何遍历System.Collections.Generic.List`1

Question

我无法从Google搜索中获得明确的指导。我有一个名为的表transaction，我想针对外键进行分组BatchID和排序descending。表定义[TTransactionID]      INT          IDENTITY (1, 1) NOT NULL,[BatchID]             INT          NULL,[CardID]              INT          NULL,[UserID]              INT          NULL,[TransactionDateTime] DATETIME     NOT NULL,[TransactionStatus]   VARCHAR (11) NOT NULL,CONSTRAINT [PK_Transactions] PRIMARY KEY CLUSTERED ([TTransactionID] ASC),CONSTRAINT [FK_Transactions_Cards] FOREIGN KEY ([CardID]) REFERENCES [dbo].[Cards] ([CardID]),CONSTRAINT [FK_Transactions_Users] FOREIGN KEY ([UserID]) REFERENCES [dbo].[Users] ([UserID]) NOT FOR REPLICATION这是我第五次尝试的代码        var TransactionList = db.Transactions                                .GroupBy(x => new { x.BatchID })                                .Select(x => x.ToList()).ToList();        int index = 0;        foreach (var item in TransactionList)        {            Response.Write( string.Format("[{0}] - {1}", index, item) );            index++;        }当我运行上面的代码时。我在浏览器上收到以下消息。我被困在这里，之后我不知道该怎么办。System.Collections.Generic.List`1[SECardDistribution.Models.Transaction]请告知谢谢

Answer 1

请注意，TransationList按BatchId升序排序，然后按CardId降序排序。

var TransactionList = context.Trx

                .GroupBy(t => t.BatchId)    //group by BatchId

                .OrderBy(t => t.Key)        //order by BatchId

                .Select

                (g =>

                    //Create a new "Batch Group" anonymously where each batch contains the associated transactions

                    new

                    {

                        BatchId = g.Key,

                        BatchTransactions = g.Select(trx => new { Card = trx.Card, User = trx.User }).OrderByDescending(batchTrx => batchTrx.Card.CardId),    //order by CardId

                    }

                );

要遍历排序列表，可以使用嵌套的foreach循环，如下所示：

//Loop through the batch group in the sorted list

            foreach(var batchGroup in TransactionList)

            {

                foreach(var batchTrx in batchGroup.BatchTransactions)

                {

                    //You may access the properties of batchTrx like a normal object graph, example batchTrx.Card.CardId

                }

            }

Answer 2

你可以SelectMany实际使用

var transactionList = db.Transactions.GroupBy(x => new { x.BatchID }).SelectMany(x => x).ToList();

Answer 3

// doing Select(x => x.ToList()) throws away group key!

var TransactionList = db.Transactions.GroupBy(x => x.BatchID).ToList();

foreach (var group in TransactionList)

{

    // now group variable is a ... well, group of transactions. :)

    // you can get its key and iterate over sub-collection of transactions in this group.

    Response.Write($"Group {group.Key}:\n");

    foreach (var item in group)

    {

        Response.Write($"    Transaction {item.TTransactionID}\n");

    }

}