XmlReader不斷讀取

Question

我有一個非常大的xml文件。 這是xml格式的簡化版本。

<?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>

我想獲取合約節點的所有信息，以及來自父節點的SponsorID。 以下是使用XmlReader部分讀取xml文件的代碼：

        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;
                            }
                        }
                    }
                }
            }                  
    }

這是問題所在。 我不能使用它，因為整個贊助樹可能對於內存來說太大了。

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

我也不能使用它，因為我不能告訴SponsorID只有Contract節點信息。

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

有沒有辦法可以在贊助商中閱讀SponsorID，向前移動光標，閱讀本贊助商下的所有合約節點，然后轉到下一個贊助商並閱讀SponsorID及其合約節點等等？

Answer 1

是的，這可以假設SponsorID始終位於Contract節點之前 。

基本思路是讀取XML文件，直到找到具有所需名稱"SponsorID"或"Contract"元素，然后將它們放到更高的處理中

    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;
            }
        }
    }

如果SponsorID始終存在並且在Contract之前，則將正確地枚舉這些元素。 但是，如果贊助商ID丟失或無序，則可能會獲得前一個贊助商的贊助商ID。 通過使用ReadSubtree()將每個“ SponsorID ”的范圍限制為包含“ Sponsor ”元素，可以捕獲此錯誤：

    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.
            }
        }
    }

然后使用它像：

        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()));
                    }
                }
            }
        }

Answer 2

嘗試這個：

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"));
            }
        }
    }
}