使用Xml.Xpath和Xml.Linq读取XML文件

Question

I am trying to read the following XML file:

<?xml version="1.0" encoding="utf-8"?>
<Connection name="default">
  <Attribute name="server" value="localhost" />
  <Attribute name="database" value="mp" />
  <Attribute name="uid" value="root" />
  <Attribute name="password" value="m123" />
  <Attribute name="code" value="MK" />
</Connection>

With the following code:

        var doc = XDocument.Load("DBConnect.xml");
        var values = doc.XPathSelectElements("//Connection[@name='default']");
        foreach (var item in values)
        {
            foreach (var att in item.Elements("Attribute"))
            {
                _server = att.Attribute("server").Value;
                _database = att.Attribute("database").Value;
                _uid = att.Attribute("uid").Value;
                _password = att.Attribute("password").Value;
                _code = att.Attribute("code").Value;
            }
        }

However, I don't seem to be getting the correct output. I am getting an error message which tells me _server is null. Any idea why? I don't think I am correctly referencing the XML attribute values I want to get a hold of.

Answer 1

One clean approach that you can use:

var values = doc.XPathSelectElements("//Connection[@name='default']")
                .Single()
                .Elements("Attribute")
                .ToDictionary(el => (string)el.Attribute("name"),
                              el => (string)el.Attribute("value"));

_server = values["server"];
_database = values["database"];
_uid = values["uid"];
_password = values["password"];
_code = values["code"];

values is an IDictionary<string, string> , so you can use it to retrieve any additional attributes that are added, without modifying the original LINQ code.

Answer 2

The issue is that you are looping through elements called Attribute and trying to find XML attributes there. Your logic would indicate that there should be all 5 XML attributes on each XML element called Attribute. Try using such code instead:

var values = doc.XPathSelectElements("//Connection[@name='default']");
_server = values.Elements("Attribute")   //look for an element called Attribute
             .Where(el => el.Attribute("name").Value == "server")  //which has attribute name="server"
             .Single()    //there should be only single element
             .Attribute("value").Value; //get the value of attribute value
// Repeat that for all other attributes (_database, _uid, etc.)

Answer 3

There is no attributes named "server", "database", "uid", "password" or "code". They're all values of the attributes named "name" which means you call Attribute("name") and not the value of it. Ex.

var attrVal = attr.Attribute("name").Value;
if (attrVal == "server")
    _server = attrVal.Value;
// ... etc

In case the above doesn't work try this.

var attrVal = attr.Attribute("name").Value;
if (attrVal == "server")
    _server = attr.Attribute("value").Value;
// ... etc