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如何迭代Linq to XML查询返回的对象集合?

linqpad ienumerable linq-to-xml

billmaya · 技术社区 · 15 年前

我有这个XML:

<BillingLog>
  <BillingItem>
    <date-and-time>2003-11-04</date-and-time>
    <application-name>Billing Service</application-name>
    <severity>Warning</severity>
    <process-id>123</process-id>
    <description>Timed out on a connection</description>
    <detail>Timed out after three retries.</detail>
  </BillingItem>
  <BillingItem>
    <date-and-time>2010-05-15</date-and-time>
    <application-name>Callback Service</application-name>
    <severity>Error</severity>
    <process-id>456</process-id>
    <description>Unable to process callback</description>
    <detail>Reconciliation timed out after two retries.</detail>
  </BillingItem>
</BillingLog>

我希望使用LinqToXML将其投影到包含在单个BillingLog对象中的BillingItem对象集合中。

public class BillingLog
{
    public IEnumerable<BillingItem> items { get; set; }
}

public class BillingItem
{
    public string Date { get; set; }
    public string ApplicationName { get; set; }
    public string Severity { get; set; }
    public int ProcessId { get; set; }
    public string Description { get; set; }
    public string Detail { get; set;}       
}

这是我用来投影XML(包含在字符串变量中)的LINQ查询来源 )

XDocument xdoc = XDocument.Parse(source);

var log = 
    from i in xdoc.Elements("BillingLog")
    select new BillingLog
    {
        items =
            from j in i.Descendants("BillingItem")
            select new BillingItem
            {
                Date = (string)j.Element("date-and-time"),
                ApplicationName = (string)j.Element("application-name"),
                Severity = (string)j.Element("severity"),
                ProcessId = (int)j.Element("process-id"),
                Description = (string)j.Element("description"),
                Detail = (string)j.Element("detail")
            }
    };

当我尝试在日志使用前述方法。

foreach (BillingItem item in log)
{
Console.WriteLine ("{0} | {1} | {2} | {3} | {4} | {5}", 
                    item.Date, item.ApplicationName, 
                    item.Severity, item.ProcessId.ToString(), 
                    item.Description, item.Detail);
}

我从LinqPad收到以下错误消息。

Cannot convert type 'UserQuery.BillingLog' to 'UserQuery.BillingItem'

事先谢谢。

1 回复 | 直到 15 年前

Fyodor Soikin 15 年前

那是因为你的 log 变量包含的集合 BillingLog 对象,而不是 BillingItem . 你必须做如下的事情:

foreach( BillingLog l in log )
{
    foreach( BillingItem item in l.items )
    {
        Console.WriteLine( ... );
    }
}

或者,如果您最初的目的是选择全部 比林项 S,无视父母 广告日志 完全可以这样重写查询:

var log = 
        from l in xdoc.Elements("BillingLog")
        from j in l.Descendants("BillingItem")
        select new BillingItem
        {
            Date = (string)j.Element("date-and-time"),
            ApplicationName = (string)j.Element("application-name"),
            Severity = (string)j.Element("severity"),
            ProcessId = (int)j.Element("process-id"),
            Description = (string)j.Element("description"),
            Detail = (string)j.Element("detail")
        }

这会给你一个简单的收藏 BillingItems 从“全部”下选择 广告日志 S,而 广告日志 S本身将被完全丢弃。