Basic Queries (LINQ to XML)

https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/basic-queries-linq-to-xml

In This Section

Topic	Description
How to: Find an Element with a Specific Attribute (C#)	Shows how to find a particular element that has an attribute that has a specific value.
How to: Find an Element with a Specific Child Element (C#)	Shows how to find a particular element that has a child element that has a specific value.
Querying an XDocument vs. Querying an XElement (C#)	Explains the differences between writing queries on an XML tree that is rooted in XElement and writing queries on an XML tree that is rooted in XDocument.
How to: Find Descendants with a Specific Element Name (C#)	Shows how to find all the descendants of an element that have a specific name. This example uses the Descendants axis.
How to: Find a Single Descendant Using the Descendants Method (C#)	Shows how to use the Descendants axis method to find a single uniquely named element.
How to: Write Queries with Complex Filtering (C#)	Shows how to write a query with a more complex filter.
How to: Filter on an Optional Element (C#)	Shows how to find nodes in an irregularly shaped tree.
How to: Find All Nodes in a Namespace (C#)	Shows how to find all nodes that are in a specific namespace.
How to: Sort Elements (C#)	Shows how to write a query that sorts its results.
How to: Sort Elements on Multiple Keys (C#)	Shows how to sort on multiple keys.
How to: Calculate Intermediate Values (C#)	Shows how to use the Let clause to calculate intermediate values in a LINQ to XML query.
How to: Write a Query that Finds Elements Based on Context (C#)	Shows how to select elements based on other elements in the tree.
How to: Debug Empty Query Results Sets (C#)	Shows the appropriate fix when debugging queries on XML that is in a default namespace.

See Also

• Querying XML Trees (C#)
• https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/programming-guide-linq-to-xml

实战

   XElement Element = XElement.Load(filePath);

删除带namespace的节点

   private void AddNewtonSoftJson()
        {
            string namespaceStr=@"{urn:schemas-microsoft-com:asm.v1}";
            string assemblyName = "Newtonsoft.Json";
            IEnumerable<XElement> newtonSoftJsonElements =
                from el in Element.Elements("runtime").Elements($"{namespaceStr}assemblyBinding").Elements($"{namespaceStr}dependentAssembly")
                where (string)el?.Element($"{namespaceStr}assemblyIdentity")?.Attribute("name") == assemblyName
                select el;
            foreach (XElement el in newtonSoftJsonElements)
            {
                el.RemoveAll();
            }
        }

批量删除system.web下的某些节点

 public void RemoveSystemWebControls()
        {
            var list = new List<string>()
            {
                "CMS.PortalControls",
                "CMS.Controls",
                "CMS.FormControls",
                "CMS.ExtendedControls",
                "System.Web.UI.DataVisualization.Charting",
                "System.Web.UI.WebControls"
            };
            IEnumerable<XElement> targetElements =
                from el in Element.Elements("system.web").Elements("pages").Elements("controls").Elements("add")
                where list.Contains(el?.Attribute("namespace")?.Value)
                select el;
            foreach (XElement el in targetElements)
            {
                el.Remove();
            }
        }

System.Xml.Linq.XElement.RemoveAll  一般用不到这个，都是用另外一个

 https://docs.microsoft.com/en-us/dotnet/api/system.xml.linq.xelement.removeall?view=netframework-4.7#System_Xml_Linq_XElement_RemoveAll

Removes nodes and attributes from this XElement.

System.Xml.Linq.Extensions.Remove<T>(IEnumerable<T>)

https://docs.microsoft.com/en-us/dotnet/api/system.xml.linq.extensions.remove?view=netframework-4.7#System_Xml_Linq_Extensions_Remove__1_System_Collections_Generic_IEnumerable___0__

Removes every node in the source collection from its parent node.

System.Xml.Linq.XContainer.Add

https://stackoverflow.com/a/41181198/3782855

https://docs.microsoft.com/en-us/dotnet/api/system.xml.linq.xcontainer.add?view=netframework-4.7#System_Xml_Linq_XContainer_Add_System_Object_

https://docs.microsoft.com/en-us/dotnet/api/system.xml.linq.xelement.parse?view=netframework-4.7#System_Xml_Linq_XElement_Parse_System_String_

  public void Add_ajaxControlToolkit()
        {
            string str = "<section name="ajaxControlToolkit" type="AjaxControlToolkit.AjaxControlToolkitConfigSection, AjaxControlToolkit" requirePermission="false" />";
            var parentElements = Element.Element("configSections");
            parentElements?.Add(XElement.Parse(str));
        }

编辑appSettings

 private void SaveSalt(string salt)
            {
                var value = $@"<add key=""CMSHashStringSalt"" value=""{salt}"" />";
                var filePath = Path.Combine(websitePath, "web.config");
                var rootElement = XElement.Load(filePath);
                var parentElement = rootElement.Element("appSettings");
                if (parentElement == null)
                {
                    throw new Exception($"Can not find appSettings section in {filePath}");
                }

                var targetElement = parentElement.Elements("add")
                    .FirstOrDefault(x => x.Attribute("key")?.Value == "CMSHashStringSalt");
                if (targetElement == null)
                {
                    parentElement.Add(XElement.Parse(value));
                }
                else
                {
                    var attribute = targetElement.Attribute("value");
                    attribute?.SetValue(salt);
                }
                rootElement.Save(filePath);
            }

  [Test]
        public void XmlTest()
        {
            string xml = "<Record ID="135" Key="CustomTableItemID" /> <Record ID="23" Key="CustomTableID" />";
            string root = $"Root{DateTime.Now:yyyyMMdd}";
            xml = $"<{root}>{xml}</{root}>";
            XElement element = XElement.Parse(xml);
            var elementName = "Record";
            var keyAttributeName = "Key";
            var idAttributeName = "ID";
            var keyValue1 = "CustomTableItemID";
            var keyValue2 = "CustomTableID";
            var node1 = element.Elements(elementName).FirstOrDefault(x => x.Attribute(keyAttributeName)?.Value == keyValue1)?.Attribute(idAttributeName)?.Value;
            Console.WriteLine(node1);
            var node2 = element.Elements(elementName).FirstOrDefault(x => x.Attribute(keyAttributeName)?.Value == keyValue2)?.Attribute(idAttributeName)?.Value;
            Console.WriteLine(node2);
        }