vb.net - 合并两个 XElement

Question

我不太确定如何问这个问题，或者这个问题是否存在，但我需要合并两个 XElement，其中一个优先于另一个，成为一个元素。

这里的首选是 VB.NET 和 Linq，但是如果任何语言都可以演示如何做到这一点，而无需我编写代码来手动分离并解析每个元素和属性，那么任何语言都会有所帮助。

例如，假设我有两个元素。幽默地告诉我他们和他们一样不同。

1.

<HockeyPlayer height="6.0" hand="left">
<Position>Center</Position>
<Idol>Gordie Howe</Idol>
</HockeyPlayer>

2.

<HockeyPlayer height="5.9" startinglineup="yes">
<Idol confirmed="yes">Wayne Gretzky</Idol>
</HockeyPlayer>

合并的结果是

<HockeyPlayer height="6.0" hand="left" startinglineup="yes">
<Position>Center</Position>
<Idol confirmed="yes">Gordie Howe</Idol>
</HockeyPlayer>

注意一些事情:#1 的 height 属性值覆盖了#2。 hand 属性和值只是从#1 复制过来的(它在#2 中不存在)。复制了 #2 中的 startinglineup 属性和值(它在 #1 中不存在)。 #1 中的 Position 元素被复制过来(它在 #2 中不存在)。 #1 中的 Idol 元素值覆盖了 #2，但 #2 的 confirmed 属性(在 #1 中不存在)被复制了。

Net net，#1 优先于 #2，其中存在冲突(意味着两者具有相同的元素和/或属性)并且没有冲突，它们都复制到最终结果。

我试过搜索这个，但似乎找不到任何东西，可能是因为我用来搜索的词太笼统了。有什么想法或解决方案(尤其是对于 Linq)？

Answer 1

为了其他人寻找相同的东西，因为我认为这两个贡献的人早就失去了兴趣......我需要做一些类似但更完整的事情。虽然仍然不完全完整，因为 XMLDoc 说它不能很好地处理非元素内容，但我不需要，因为我的非元素内容要么是文本，要么不重要。随意增强和重新发布...哦，它是 C# 4.0，因为这就是我使用的......

/// <summary>
/// Provides facilities to merge 2 XElement or XML files. 
/// <para>
/// Where the LHS holds an element with non-element content and the RHS holds 
/// a tree, the LHS non-element content will be applied as text and the RHS 
/// tree ignored. 
/// </para>
/// <para>
/// This does not handle anything other than element and text nodes (infact 
/// anything other than element is treated as text). Thus comments in the 
/// source XML are likely to be lost.
/// </para>
/// <remarks>You can pass <see cref="XDocument.Root"/> if it you have XDocs 
/// to work with:
/// <code>
/// XDocument mergedDoc = new XDocument(MergeElements(lhsDoc.Root, rhsDoc.Root);
/// </code></remarks>
/// </summary>
public class XmlMerging
{
    /// <summary>
    /// Produce an XML file that is made up of the unique data from both
    /// the LHS file and the RHS file. Where there are duplicates the LHS will 
    /// be treated as master
    /// </summary>
    /// <param name="lhsPath">XML file to base the merge off. This will override 
    /// the RHS where there are clashes</param>
    /// <param name="rhsPath">XML file to enrich the merge with</param>
    /// <param name="resultPath">The fully qualified file name in which to 
    /// write the resulting merged XML</param>
    /// <param name="options"> Specifies the options to apply when saving. 
    /// Default is <see cref="SaveOptions.OmitDuplicateNamespaces"/></param>
    public static bool TryMergeXmlFiles(string lhsPath, string rhsPath, 
        string resultPath, SaveOptions options = SaveOptions.OmitDuplicateNamespaces)
    {
        try
        {
            MergeXmlFiles(lhsPath, rhsPath, resultPath);
        }
        catch (Exception)
        {
            // could integrate your logging here
            return false;
        }
        return true;
    }

    /// <summary>
    /// Produce an XML file that is made up of the unique data from both the LHS
    /// file and the RHS file. Where there are duplicates the LHS will be treated 
    /// as master
    /// </summary>
    /// <param name="lhsPath">XML file to base the merge off. This will override 
    /// the RHS where there are clashes</param>
    /// <param name="rhsPath">XML file to enrich the merge with</param>
    /// <param name="resultPath">The fully qualified file name in which to write 
    /// the resulting merged XML</param>
    /// <param name="options"> Specifies the options to apply when saving. 
    /// Default is <see cref="SaveOptions.OmitDuplicateNamespaces"/></param>
    public static void MergeXmlFiles(string lhsPath, string rhsPath, 
        string resultPath, SaveOptions options = SaveOptions.OmitDuplicateNamespaces)
    {
        XElement result = 
            MergeElements(XElement.Load(lhsPath), XElement.Load(rhsPath));
        result.Save(resultPath, options);
    }

    /// <summary>
    /// Produce a resulting <see cref="XElement"/> that is made up of the unique 
    /// data from both the LHS element and the RHS element. Where there are 
    /// duplicates the LHS will be treated as master
    /// </summary>
    /// <param name="lhs">XML Element tree to base the merge off. This will 
    /// override the RHS where there are clashes</param>
    /// <param name="rhs">XML element tree to enrich the merge with</param>
    /// <returns>A merge of the left hand side and right hand side element 
    /// trees treating the LHS as master in conflicts</returns>
    public static XElement MergeElements(XElement lhs, XElement rhs)
    {
        // if either of the sides of the merge are empty then return the other... 
        // if they both are then we return null
        if (rhs == null) return lhs;
        if (lhs == null) return rhs;

        // Otherwise build a new result based on the root of the lhs (again lhs 
        // is taken as master)
        XElement result = new XElement(lhs.Name);

        MergeAttributes(result, lhs.Attributes(), rhs.Attributes());

        // now add the lhs child elements merged to the RHS elements if there are any
        MergeSubElements(result, lhs, rhs);
        return result;
    }

    /// <summary>
    /// Enrich the passed in <see cref="XElement"/> with the contents of both 
    /// attribute collections.
    /// Again where the RHS conflicts with the LHS, the LHS is deemed the master
    /// </summary>
    /// <param name="elementToUpdate">The element to take the merged attribute 
    /// collection</param>
    /// <param name="lhs">The master set of attributes</param>
    /// <param name="rhs">The attributes to enrich the merge</param>
    private static void MergeAttributes(XElement elementToUpdate, 
        IEnumerable<XAttribute> lhs, IEnumerable<XAttribute> rhs)
    {
        // Add in the attribs of the lhs... we will only add new attribs from 
        // the rhs duplicates will be ignored as lhs is master
        elementToUpdate.Add(lhs);

        // collapse the element names to save multiple evaluations... also why 
        // we ain't putting this in as a sub-query
        List<XName> lhsAttributeNames = 
            lhs.Select(attribute => attribute.Name).ToList();
        // so add in any missing attributes
        elementToUpdate.Add(rhs.Where(attribute => 
            !lhsAttributeNames.Contains(attribute.Name)));
    }

    /// <summary>
    /// Enrich the passed in <see cref="XElement"/> with the contents of both 
    /// <see cref="XElement.Elements()"/> subtrees.
    /// Again where the RHS conflicts with the LHS, the LHS is deemed the master.
    /// Where the passed elements do not have element subtrees, but do have text 
    /// content that will be used. Again the LHS will dominate
    /// </summary>
    /// <remarks>Where the LHS has text content and no subtree, but the RHS has 
    /// a subtree; the LHS text content will be used and the RHS tree ignored. 
    /// This may be unexpected but is consistent with other .NET XML 
    /// operations</remarks>
    /// <param name="elementToUpdate">The element to take the merged element 
    /// collection</param>
    /// <param name="lhs">The element from which to extract the master 
    /// subtree</param>
    /// <param name="rhs">The element from which to extract the subtree to 
    /// enrich the merge</param>
    private static void MergeSubElements(XElement elementToUpdate, 
        XElement lhs, XElement rhs)
    {
        // see below for the special case where there are no children on the LHS
        if (lhs.Elements().Count() > 0)
        {
            // collapse the element names to a list to save multiple evaluations...
            // also why we ain't putting this in as a sub-query later
            List<XName> lhsElementNames = 
                lhs.Elements().Select(element => element.Name).ToList();

            // Add in the elements of the lhs and merge in any elements of the 
            //same name on the RHS
            elementToUpdate.Add(
                lhs.Elements().Select(
                    lhsElement => 
                        MergeElements(lhsElement, rhs.Element(lhsElement.Name))));

            // so add in any missing elements from the rhs
            elementToUpdate.Add(rhs.Elements().Where(element => 
                !lhsElementNames.Contains(element.Name)));
        }
        else
        {
            // special case for elements where they have no element children 
            // but still have content:
            // use the lhs text value if it is there
            if (!string.IsNullOrEmpty(lhs.Value))
            {
                elementToUpdate.Value = lhs.Value;
            }
            // if it isn't then see if we have any children on the right
            else if (rhs.Elements().Count() > 0)
            {
                // we do so shove them in the result unaltered
                elementToUpdate.Add(rhs.Elements());
            }
            else
            {
                // nope then use the text value (doen't matter if it is empty 
                //as we have nothing better elsewhere)
                elementToUpdate.Value = rhs.Value;
            }
        }
    }
}