样例XML
<?xml version="1.0" encoding="utf-8" ?>
<pets>
<pet>
<id>1
</id>
<name>Duke
</name>
<species>Great Dane
</species>
<sex>Male
</sex>
<startYear>1968
</startYear>
<endYear>1970
</endYear>
<causeOfDeath>Suicide
</causeOfDeath>
<specialQuality>Big and goofy
</specialQuality>
</pet>
<pet>
<id>2
</id>
<name>Dog
</name>
<species>Some Kind of Cat
</species>
<sex>Female
</sex>
<startYear>1972
</startYear>
<endYear>1974
</endYear>
<causeOfDeath>Car
</causeOfDeath>
<specialQuality>Best mouser
</specialQuality>
</pet>
<pet>
<id>3
</id>
<name>Sam
</name>
<species>Labrador
</species>
<sex>Female
</sex>
<startYear>1973
</startYear>
<endYear>1980
</endYear>
<causeOfDeath>Old Age
</causeOfDeath>
<specialQuality>Great hunting dog
</specialQuality>
</pet>
<pet>
<id>4
</id>
<name>Hogan
</name>
<species>Yellow Lab Mix
</species>
<sex>Male
</sex>
<startYear>1994
</startYear>
<endYear>2004
</endYear>
<causeOfDeath>Seizure
</causeOfDeath>
<specialQuality>A very good dog
</specialQuality>
</pet>
<pet>
<id>5
</id>
<name>Leda
</name>
<species>Chocolate Labradour
</species>
<sex>Female
</sex>
<startYear>2004
</startYear>
<endYear></endYear>
<causeOfDeath></causeOfDeath>
<specialQuality>Thumper
</specialQuality>
</pet>
<pet>
<id>6
</id>
<name>Po
</name>
<species>Toy Poodle
</species>
<sex>Female
</sex>
<startYear>2003
</startYear>
<endYear>2004
</endYear>
<causeOfDeath>Lethal Injection
</causeOfDeath>
<specialQuality>Mental
</specialQuality>
</pet>
<pet>
<id>7
</id>
<name>Big Mama
</name>
<species>Tabby
</species>
<sex>Female
</sex>
<startYear>1998
</startYear>
<endYear></endYear>
<causeOfDeath></causeOfDeath>
<specialQuality>Quarterback
</specialQuality>
</pet>
<pet>
<id>8
</id>
<name>Ruby
</name>
<species>Rotweiller
</species>
<sex>Female
</sex>
<startYear>1997
</startYear>
<endYear></endYear>
<causeOfDeath></causeOfDeath>
<specialQuality>Big baby
</specialQuality>
</pet>
<pet>
<id>9
</id>
<name>Nala
</name>
<species>Maine Coon
</species>
<sex>Female
</sex>
<startYear>2007
</startYear>
<endYear></endYear>
<causeOfDeath></causeOfDeath>
<specialQuality>El Freako
</specialQuality>
</pet>
</pets>
加载XML文档
对于LINQ to XML，需要加载一个XML文档以便将数据获取到内存中。可以用System.Xml.Linq.XDocument或System.Xml.Linq.XElement的实例来加载XML文档，也可以用XElement.Parse将字符串形式的XML文档转换成XML。
System.Xml.Linq.XDocument.Load(xml_file_name) 从根节点开始加载整个XML文档System.Xml.Linq.XElement.Load(xml_file_name) 该方法也会加载跟节点，不过在查询时会忽略根节点 XDocument.Load和XElement.Load都有一些冲澡版本，可以接收字符串文件名、TextReader或XmlReader。其中，有个版本(Load(string, LoadOptions))从文件加载XML，LoadOption可以保留空白、设置基统一资源定位符(URI)或从XmlReader中获取行信息。LoadOptions枚举的选项有None、PreserveWhitespace、SetBaseUri和SetLineInfo。
查询XML
使用XDocument
class Program
{
static void Main(string[] args
)
{
XDocument xml
= XDocument
.Load("..\\..\\PetCemetary.xml");
var pets
= from pet
in xml
.Elements("pets").Elements("pet") select pet
;
Array
.ForEach(pets
.ToArray(), p
=> Console
.WriteLine(p
.Element("name").Value
));
}
}
使用XElement
class Program
{
static void Main(string[] args
)
{
XElement xml
= XElement
.Load("..\\..\\PetCemetary.xml");
var pets
= from pet
in xml
.Elements("pet") select pet
;
Array
.ForEach(pets
.ToArray(), p
=> Console
.WriteLine(p
.Element("name").Value
));
}
}
管理属性
class Program
{
static void Main(string[] args
)
{
XElement xml
= XElement
.Load("..\\..\\PetCemetary.xml");
var pets
= from pet
in xml
.Elements("pet")
let genus
= pet
.Element("species").Attribute("genus")
where genus
.Value
== "Feline"
select pet
;
Array
.ForEach(pets
.ToArray(), p
=> Console
.WriteLine(p
.Element("name").Value
));
}
}
添加属性
class Program
{
static void Main(string[] args
)
{
string filename
= "..\\..\\PetCemetary.xml";
XElement xml
= XElement
.Load(filename
);
var pets
= from pet
in xml
.Elements("pet")
let genus
= pet
.Element("species").Attribute("genus")
where genus
== null
select pet
;
Array
.ForEach(pets
.ToArray(), p
=> Console
.WriteLine(p
.Element("name").Value
));
foreach (var pet
in pets
)
{
pet
.Element("species").Add(new XAttribute("genus", "Dog"));
}
xml
.Save(filename
);
}
}
删除属性
class Program
{
static void Main(string[] args
)
{
string filename
= "..\\..\\PetCemetary.xml";
XElement xml
= XElement
.Load(filename
);
var pets
= from pet
in xml
.Elements("pet")
where pet
.Element("name").Value
== "Ruby"
select pet
;
Array
.ForEach(pets
.ToArray(), p
=> Console
.WriteLine(p
.Element("name").Value
));
foreach (var pet
in pets
)
{
pet
.Element("species").Attribute("genus").Remove();
}
xml
.Save(filename
);
}
}
从字符串中加载XML
class Program
{
static void Main(string[] args
)
{
string xml
= "<pets>" +
" <pet>" +
" <id>2</id>" +
" <name>Dog</name>" +
" <species>Some Kind of Cat</species>" +
" <sex>Female</sex>" +
" <startYear>1972</startYear>" +
" <endYear>1974</endYear>" +
" <causeOfDeath>Car</causeOfDeath>" +
" <specialQuality>Best mouser</specialQuality>" +
" </pet>" +
"</pets>";
XElement elem
= XElement
.Parse(xml
);
var pets
= from pet
in elem
.Elements("pet") select pet
;
Array
.ForEach(pets
.ToArray(), p
=> Console
.WriteLine(p
.Element("name").Value
));
}
}
处理缺失的数据
有些数据可能并没有出现在XML中。比如说，XML中允许出现没有数据的元素。
class Program
{
static void Main(string[] args
)
{
XElement elem
= XElement
.Load(@"..\..\PetCemetary.xml");
var pets
= from pet
in elem
.Elements("pet")
select new
{
Name
= pet
.Name
,
StartYear
= (int)pet
.Element("startYear"),
EndYear
= (int)(pet
.Element("endYear").IsEmpty
? 0 : (int)pet
.Element("endYear"))
};
Array
.ForEach(pets
.ToArray(), p
=>
{
Console
.WriteLine("Name: {0}", p
.Name
);
Console
.WriteLine("Entered family: {0}", p
.StartYear
);
Console
.WriteLine("Left family: {0}", p
.EndYear
);
});
}
}
使用查询表达式和XML数据
样例XML数据
<?xml version="1.0" encoding="utf-8" ?>
<sq:Stocks xmlns:sq="http://www.stock_quotes.com">
<sq:Stock>
<sq:Symbol>MSFT
</sq:Symbol>
<sq:Price Change="0.6" Low="42.1" High="51.0">56.0
</sq:Price>
</sq:Stock>
<sq:Stock>
<sq:Symbol>MVK
</sq:Symbol>
<sq:Price Change="-3.2" Low="22.8" High="32.4">25.5
</sq:Price>
</sq:Stock>
<sq:Stock>
<sq:Symbol>GOOG
</sq:Symbol>
<sq:Price Change="8.0" Low="24.4" High="34.5">32.0
</sq:Price>
</sq:Stock>
<sq:Stock>
<sq:Symbol>VFINX
</sq:Symbol>
<sq:Price Change="8.0" Low="24.4" High="34.5">32.0
</sq:Price>
</sq:Stock>
<sq:Stock>
<sq:Symbol>HDPMX
</sq:Symbol>
<sq:Price Change="8.0" Low="24.4" High="34.5">32.0
</sq:Price>
</sq:Stock>
</sq:Stocks>
使用命名空间
上面的样例XML相比于之前的XML在结构上有个重要的区别是：它添加了一个命名空间(即xmlns 属性)。下面的例子中，定义了一个XNamespace对象，然后再查询XML文件时，将其作为所有使用了这个命名空间的元素的前缀。
class Program
{
static void Main(string[] args
)
{
const string filename
= "..\\..\\Stocks.xml";
XElement xml
= XElement
.Load(filename
);
XNamespace sq
= "http://www.stock_quotes.com";
var stocks
= from stock
in xml
.Elements(sq
+ "Stock")
select new { Name
= stock
.Element(sq
+ "Symbol").Value
};
Array
.ForEach(stocks
.ToArray(), o
=> Console
.WriteLine(o
.Name
));
}
}
嵌套查询
class Program
{
static void Main(string[] args
)
{
const string filename
= "..\\..\\Stocks.xml";
XElement xml
= XElement
.Load(filename
);
XNamespace sq
= "http://www.stock_quotes.com";
var stocks
=from stock
in xml
.Elements(sq
+ "Stock")
where (from symbol
in stock
.Elements(sq
+ "Symbol") select symbol
).Any()
select new { Name
= stock
.Element(sq
+ "Symbol").Value
};
Array
.ForEach(stocks
.ToArray(), o
=> Console
.WriteLine(o
.Name
));
}
}
使用Where子句进行筛选
class Program
{
static void Main(string[] args
)
{
const string filename
= "..\\..\\Stocks.xml";
XElement xml
= XElement
.Load(filename
);
XNamespace sq
= "http://www.stock_quotes.com";
var stocksThatLostGround
=
from stock
in xml
.Elements(sq
+ "Stock")
where (
from price
in stock
.Elements(sq
+ "Price")
where (decimal)price
.Attribute("Change") < 0 select price
).Any()
select stock
;
Array
.ForEach(stocksThatLostGround
.ToArray(), o
=> Console
.WriteLine(o
.Element(sq
+ "Symbol").Value
));
}
}
根据上下文查找元素
class Program
{
static void Main(string[] args
)
{
XElement elem
= XElement
.Parse(
"<?xml version=\"1.0\" encoding=\"utf-8\" ?>" +
"<sq:Stocks xmlns:sq=\"http://www.stock_quotes.com\">" +
" <sq:Stock>" +
" <sq:Symbol>MSFT</sq:Symbol>" +
" <sq:Price Change=\"0.6\" Low=\"42.1\" High=\"51.0\">56.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>MVK</sq:Symbol>" +
" <sq:Price Change=\"-3.2\" Low=\"22.8\" High=\"32.4\">25.5</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>GOOG</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>VFINX</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>HDPMX</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
"</sq:Stocks>");
XNamespace sq
= "http://www.stock_quotes.com";
var contextStock
=
from symbol
in elem
.Elements(sq
+ "Stock").Elements(sq
+ "Symbol")
let price
= symbol
.ElementsAfterSelf().FirstOrDefault()
where (decimal)(price
.Attribute("Change")) < 1M
select symbol
;
Array
.ForEach(contextStock
.ToArray(), o
=> Console
.WriteLine(o
.Value
));
}
}
对XML查询进行排序
class Program
{
static void Main(string[] args
)
{
XElement elem
= XElement
.Parse(
"<?xml version=\"1.0\" encoding=\"utf-8\" ?>" +
"<sq:Stocks xmlns:sq=\"http://www.stock_quotes.com\">" +
" <sq:Stock>" +
" <sq:Symbol>MSFT</sq:Symbol>" +
" <sq:Price Change=\"0.6\" Low=\"42.1\" High=\"51.0\">56.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>MVK</sq:Symbol>" +
" <sq:Price Change=\"-3.2\" Low=\"22.8\" High=\"32.4\">25.5</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>GOOG</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>VFINX</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>HDPMX</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
"</sq:Stocks>");
XNamespace sq
= "http://www.stock_quotes.com";
var contextStock
=
from symbol
in elem
.Elements(sq
+ "Stock").Elements(sq
+ "Symbol")
let price
= symbol
.ElementsAfterSelf().FirstOrDefault()
where (decimal)(price
.Attribute("Change")) < 1M
orderby (decimal)price
.Attribute("Change")
select symbol
;
Array
.ForEach(contextStock
.ToArray(), o
=> Console
.WriteLine(o
.Value
));
}
}
通过let计算中间值
class Program
{
static void Main(string[] args
)
{
XElement elem
= XElement
.Parse(
"<?xml version=\"1.0\" encoding=\"utf-8\" ?>" +
"<sq:Stocks xmlns:sq=\"http://www.stock_quotes.com\">" +
" <sq:Stock>" +
" <sq:Symbol>MSFT</sq:Symbol>" +
" <sq:Price Change=\"0.6\" Low=\"42.1\" High=\"51.0\">56.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>MVK</sq:Symbol>" +
" <sq:Price Change=\"-3.2\" Low=\"22.8\" High=\"32.4\">25.5</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>GOOG</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>VFINX</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
" <sq:Stock>" +
" <sq:Symbol>HDPMX</sq:Symbol>" +
" <sq:Price Change=\"8.0\" Low=\"24.4\" High=\"34.5\">32.0</sq:Price>" +
" </sq:Stock>" +
"</sq:Stocks>");
XNamespace sq
= "http://www.stock_quotes.com";
var stockSpreads
=
from stock
in elem
.Elements(sq
+ "Stock")
let spread
= (decimal)stock
.Element(sq
+ "Price").Attribute("High") -
(decimal)stock
.Element(sq
+ "Price").Attribute("Low")
orderby spread
descending
select new { Symbol
= stock
.Element(sq
+ "Symbol").Value
, Spread
= spread
};
Array
.ForEach(stockSpreads
.ToArray(), o
=> Console
.WriteLine(o
));
}
}
节点批注
class Program
{
static void Main(string[] args
)
{
const string filename
= "..\\..\\Stocks.xml";
XElement elem
= XElement
.Load(filename
);
XNamespace sq
= "http://www.stock_quotes.com";
var stocksToAnnotate
=
from stock
in elem
.Elements(sq
+ "Stock")
select stock
;
const string yahooQuery
= "http://download.finance.yahoo.com/d/?s={0}&f=ncbh";
foreach (var stock
in stocksToAnnotate
)
{
stock
.AddAnnotation(string.Format(yahooQuery
, stock
.Element(sq
+ "Symbol").Value
));
Console
.WriteLine(stock
.Annotation(typeof(Object
)));
}
}
}
