XmlReader连续读取

本文关键字：读取 连续 XmlReader | 更新日期: 2023-09-27 17:59:53

我有一个很大的xml文件。这是xml格式的简化版本。

<?xml version='1.0' encoding='UTF-8'?>
<Sender>
 <SenderID>571099948</SenderID>
 <Sponsors>
  <Sponsor>
    <SponsorID>TEST01</SponsorID>
    <Contracts>
      <Contract>
        <ContractID>000001</ContractID>
        <Member>
          <SSN>1111111111</SSN>
          <Gender>M</Gender>
          <Benefits>
            <Benefit BenefitType="AAA">
            </Benefit>
            <Benefit BenefitType="BBB">
            </Benefit>
          </Benefits>
        </Member>
        <Member>
          <SSN>4444444444</SSN>
          <Gender>F</Gender>
          <Benefits>
            <Benefit BenefitType="AAA">
            </Benefit>
          </Benefits>
        </Member>
      </Contract>
      <Contract>
        <ContractID>0000002</ContractID>
        <Member>
          <SSN>2222222222</SSN>
          <Gender>F</Gender>
          <Benefits>
            <Benefit BenefitType="CCC">
            </Benefit>
            <Benefit BenefitType="DDD">
            </Benefit>
          </Benefits>
        </Member>
      </Contract>
      <Contract>
        <ContractID>0000003</ContractID>
        <Member>
          <SSN>333333333</SSN>
          <Gender>F</Gender>
          <Benefits> 
            <Benefit BenefitType="CCC">
            </Benefit>
          </Benefits>
        </Member>
      </Contract>
    </Contracts>
  </Sponsor>
  <Sponsor>
    <SponsorID>TEST02</SponsorID>
    <Contracts>
      <Contract>
        <ContractID>0000011</ContractID>
        <Member>
          <SSN>1111111111</SSN>
          <Gender>M</Gender>
          <Benefits>
          </Benefits>
        </Member>
      </Contract>
      <Contract>
        <ContractID>0000002</ContractID>
        <Member>
          <SSN>2222222222</SSN>
          <Gender>F</Gender>
          <Benefits>
          </Benefits>
        </Member>
      </Contract>
    </Contracts>
  </Sponsor>
</Sponsors>
</Sender>

我想从父节点获得合同节点的所有信息，以及SponsorID。以下是使用XmlReader:部分读取xml文件的代码

        static IEnumerable<XElement> SimpleStreamAxis(string inputUrl, string elementName)      
    {
            using (XmlReader reader = XmlReader.Create(inputUrl))
            {
                reader.MoveToContent();
                while (reader.Read())
                {
                    if (reader.NodeType == XmlNodeType.Element)
                    {
                        if (reader.Name == elementName)
                        {
                            XElement el = XNode.ReadFrom(reader) as XElement;
                            if (el != null)
                            {
                                yield return el;
                            }
                        }
                    }
                }
            }                  
    }

这就是问题所在。我不能使用这个，因为整个赞助商树对于内存来说可能太大了。

var sponsor = SimpleStreamAxis(file, "Sponsor");

我也不能使用这个，因为我不能只告诉SponsorID合同节点信息。

var contract = SimpleStreamAxis(file, "Contract");

有没有一种方法可以让我在Sponsor中读取SponsorID，向前移动光标，读取该Sponsor下的所有合同节点，然后移动到下一个Sponsor，读取Sponsor ID及其合同节点，依此类推？

XmlReader连续读取

试试这个：

using (XmlReader xmlReader = XmlReader.Create("file.xml"))
{
    while (xmlReader.Read())
    {
        if (xmlReader.ReadToFollowing("SponsorID"))
        {
            string sponsorId = xmlReader.ReadElementContentAsString();
            // process SponsorID
            Console.WriteLine(sponsorId);
            if (xmlReader.ReadToFollowing("Contract"))
            {
                do
                {
                    XmlReader contractSubtree = xmlReader.ReadSubtree();
                    XElement contractElement = XElement.Load(contractSubtree);
                    // process Contract
                    Console.WriteLine(contractElement.Element("ContractID"));
                } while (xmlReader.ReadToNextSibling("Contract"));
            }
        }
    }
}

是的，这可以在假设SponsorID总是在Contract节点之前完成。

基本思想是通读XML文件，直到找到具有所需名称"SponsorID"或"Contract"的元素，然后生成它们以进行更高的处理

    public static IEnumerable<XElement> StreamNamedElements(XmlReader reader, IEnumerable<XName> names)
    {
        var nameSet = new HashSet<XName>(names);
        while (reader.Read())
        {
            if (reader.NodeType == XmlNodeType.Element && nameSet.Contains(XName.Get(reader.LocalName, reader.NamespaceURI)))
            {
                XElement el = XNode.ReadFrom(reader) as XElement;
                if (el != null)
                    yield return el;
            }
        }
    }

在SponsorID总是存在并且在Contract之前的情况下，这将正确地枚举这些元素。但是，如果赞助商ID丢失或出现故障，则可能会拾取以前赞助商的赞助商ID。通过使用ReadSubtree():将每个"SponsorID"的范围限制为包含的"Sponsor"元素，可以捕获此错误

    public static IEnumerable<XmlReader> StreamNamedSubtrees(XmlReader reader, IEnumerable<XName> names)
    {
        var nameSet = new HashSet<XName>(names);
        while (reader.Read())
        {
            if (reader.NodeType == XmlNodeType.Element && nameSet.Contains(XName.Get(reader.LocalName, reader.NamespaceURI)))
            {
                var subReader = reader.ReadSubtree();
                yield return subReader;
                ((IDisposable)subReader).Dispose(); // Be sure to advance to the end of the subtree if the caller did not.
            }
        }
    }

然后像这样使用：

        using (var sr = new StringReader(xml))
        using (var reader = XmlReader.Create(sr))
        {
            foreach (var subReader in StreamNamedSubtrees(reader, new[] { (XName)"Sponsor" }))
            {
                XElement sponsorID = null;
                foreach (var el in StreamNamedElements(subReader, new[] { (XName)"SponsorID", (XName)"Contract" }))
                {
                    if (el.Name == "SponsorID")
                    {
                        sponsorID = el;
                    }
                    else if (el.Name == "Contract")
                    {
                        if (sponsorID == null)
                            throw new InvalidOperationException();
                        // Example "higher processing"
                        Debug.WriteLine(string.Format("{0}: {1}", sponsorID.Value, el.ToString()));
                    }
                }
            }
        }
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