static void Main(string[] args)
{
#if false
// X-DOM Overview 文档对象模型 概述
{
XElement config = XElement.Parse(
@"<configuration>
<client enabled='true'>
<timeout>30</timeout>
</client>
</configuration>");
foreach (XElement child in config.Elements())
{
child.Name.Dump("Child element name");
}
XElement client = config.Element("client");
bool enabled = (bool)client.Attribute("enabled"); // Read attribute
enabled.Dump("enabled attribute");
client.Attribute("enabled").SetValue(!enabled); // Update attribute
int timeout = (int)client.Element("timeout"); // Read element
timeout.Dump("timeout element");
client.Element("timeout").SetValue(timeout * 2); // Update element
client.Add(new XElement("retries", 3)); // Add new elememt
}
// Instantiation X-DOM 实例化 X-DOM
{
// 方法 添加 元素节点 节点值 属性 熟悉值
XElement lastName = new XElement("lastname", "Bloggs");
lastName.Add(new XComment("nice name"));
XElement customer = new XElement("customer");
customer.Add(new XAttribute("id", 123));
customer.Add(new XElement("firstname", "Joe"));
customer.Add(lastName);
customer.Dump();
// Functional Construction 函数式构建
new XElement("customer", new XAttribute("id", 123),
new XElement("firstname", "joe"),
new XElement("lastname", "bloggs",
new XComment("nice name")
)
);
// Fucntional Construction from Database Query 为每个实体对象 创建 元素节点
NutshellEntities dataContext = new NutshellEntities();
new XElement("customers",
from c in dataContext.Customer
select new XElement("customer",
new XAttribute("id", c.ID),
new XElement("name", c.Name,
new XComment("nice name"))));
// Automatic Deep Cloing 自动深度克隆
var address =
new XElement("address",
new XElement("street", "Lawley St"),
new XElement("town", "North Beach")
);
var customer1 = new XElement("customer1", address);
var customer2 = new XElement("customer2", address);
customer1.Element("address").Element("street").Value = "Another St";
Console.WriteLine(customer2.Element("address").Element("street").Value);
}
#elif false
// Navigating and Querying 导航查询
{
// FirstNode LastNode and Nodes
var bench =
new XElement("bench",
new XElement("toolbox",
new XElement("handtool", "Hammer"),
new XElement("handtool", "Rasp")
),
new XElement("toolbox",
new XElement("handtool", "Saw"),
new XElement("powertool", "Nailgun")
),
new XComment("Be careful with the nailgun")
);
bench.FirstNode.Dump("FirstNode");
bench.LastNode.Dump("LastNode");
foreach (XNode node in bench.Nodes())
{
Console.WriteLine(node.ToString(SaveOptions.DisableFormatting) + "."); // toolbox = HammerRasp
}
// toolbox = SawNailgun
// Enumerating Elements 检索元素
foreach (XElement e in bench.Elements())
{
Console.WriteLine(e.Name + "=" + e.Value);
}
// Quering Elements
IEnumerable <string> toolboxWithNailgun = from toolbox in bench.Elements()
where toolbox.Elements().Any(tool => tool.Value == "Nailgun")
select toolbox.Value;
var handTools = from toolbox in bench.Elements()
from tool in toolbox.Elements()
where tool.Name == "handtool"
select tool.Value;
int toolboxCount = bench.Elements("toolbox").Count();
var handTools2 =
from tool in bench.Elements("toolbox").Elements("handtool")
select tool.Value.ToUpper();
toolboxWithNailgun.Dump("The toolbox with the nailgun");
handTools.Dump("The hand tools in all toolboxes");
toolboxCount.Dump("Number of toolboxes");
handTools2.Dump("The hand tools in all toolboxes");
XElement singnal = bench.Element("toolbox").Element("xyc");
string nullableValue = singnal?.Value;
// Quering Elements - Recursive
// Descendants 返回所有叶子节点 并 可筛选
// DescendantNodes 返回包含所有的父节点 和 叶子节点
bench.Descendants("handtool").Count().Dump();
foreach (XNode node in bench.DescendantNodes())
{
Console.WriteLine(node.ToString(SaveOptions.DisableFormatting));
}
(
from c in bench.DescendantNodes().OfType <XComment>()
where c.Value.Contains("careful")
orderby c.Value
select c.Value
).Dump("Comments anywhere in the X-DOM containing the word 'careful'");
}
#elif false
// Updating X-DOM 更新 X-DOM
{
// SetValue Replaces Child Content
XElement settings =
new XElement("settings",
new XElement("timeout", 30));
settings.Dump("Original XML");
settings.SetValue("blah");
settings.Dump("Notice the timeout node has disappeared");
// SetElementValue 添加或覆盖
XElement settings2 = new XElement("settings");
settings.SetElementValue("timeout", 30); settings2.Dump("Adds child element");
settings.SetElementValue("timeout", 60); settings2.Dump("Updates child element");
// AddAfterSelf Remove Replace
XElement items =
new XElement("items",
new XElement("one"),
new XElement("three")
);
items.Dump("Original XML");
items.FirstNode.AddAfterSelf(new XElement("two"));
items.Dump("After calling items.FirstNode.AddAfterSelf");
items.FirstNode.ReplaceWith(new XComment("One was here"));
items.Dump("After calling ReplaceWith");
XElement contacts = XElement.Parse(@"
<contacts>
<customer name='Mary'/>
<customer name='Chris' archived='true'/>
<supplier name='Susan'>
<phone archived='true'>012345678<!--confidential--></phone>
</supplier>
</contacts>");
contacts.Dump("Before");
contacts.Elements("customer").Remove();
contacts.Dump("After");
contacts.Dump("Before");
contacts.Elements() // <customer name='Chris' archived='true'/> 被移除
.Where(e1 => (bool?)e1.Attribute("archived") == true)
.Remove();
contacts.Dump("After");
contacts.Dump("Before");
contacts.Descendants() // 所有 属性archived的值为 true 的元素被移除
.Where(e2 => (bool?)e2.Attribute("archived") == true)
.Remove();
contacts.Dump("After");
contacts.Dump("Before");
contacts.Elements()
.Where(e3 => e3.DescendantNodes().OfType <XComment>().Any(c => c.Value == "confidential"))
.Remove();
contacts.Dump("After");
contacts.Descendants().OfType <XComment>().Remove(); // 移除整个树🌳中的注释节点
contacts.DescendantNodes().OfType <XComment>().Remove();
// Get and Set Value
var e = new XElement("date", DateTime.Now);
e.SetValue(DateTime.Now.AddDays(1));
e.Value.Dump();
DateTime dt = (DateTime)e;
XAttribute a = new XAttribute("resolution", 1.234);
double res = (double)a;
// Nullables 可空类型
int? timeout = (int?)e.Element("timeout");
double resolution = (double?)e.Attribute("resolution") ?? 1.0;
var nullXe = new XElement("Empty");
try
{
int timeout1 = (int)nullXe.Element("timeout");
}
catch (Exception ex)
{
ex.Message.Dump("Element (\"timeout\") returns null so the result cannot be cast to int");
}
int?timeout2 = (int?)nullXe.Element("timeout");
timeout2.Dump("Casting to a nullable type solve this problem");
var data = XElement.Parse(@"
<data>
<customer id='1' name='Mary' credit='100' />
<customer id='2' name='John' credit='150' />
<customer id='3' name='Anne' />
</data>");
IEnumerable <string> query =
from cust in data.Elements()
where (int?)cust.Attribute("credit") > 100 // 属性值转换为 nullable，避免 NullReferenceException
select cust.Attribute("name").Value;
query.Dump();
IEnumerable <string> query2 =
from cust in data.Elements()
where cust.Attributes("credit").Any() && (int)cust.Attribute("credit") > 100
select cust.Attribute("name").Value;
query2.Dump();
// XText 与 XElement 混合内容
XElement summary =
new XElement("summary",
new XText("An XAttribute is "),
new XElement("bold", "not"),
new XText(" an XNode")
);
summary.Dump(); // An XAttribute is not an XNode
{
var e1 = new XElement("test", "Hello");
e1.Add("World");
var e2 = new XElement("test", "Hello", "World");
var e3 = new XElement("test", new XText("Hello"), new XText("World"));
e1.Dump(); e2.Dump(); e3.Dump(); // 均输出 Hello World
e1.Nodes().Count().Dump("Number of children in e1"); // 均为 2
e2.Nodes().Count().Dump("Number of children in e2");
e3.Nodes().Count().Dump("Number of children in e3");
}
}
#elif false
// Documents and Declarations 文档和声明
{
// Building an XHTML document 建立一个XHTML 文档{
{
var styleInstruction = new XProcessingInstruction(
"xml-stylesheet", "href='styles.css' type='text/css'");
var docType = new XDocumentType("html",
"-//W3C//DTD XHTML 1.0 Strict//EN",
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd", null);
XNamespace ns = "http://www.w3.org/1999/xhtml";
var root =
new XElement(ns + "html",
new XElement(ns + "head",
new XElement(ns + "title", "An XHTML page")),
new XElement(ns + "body",
new XElement(ns + "h1", "This is a heading."),
new XElement(ns + "p", "This is some content."))
);
var doc =
new XDocument(
new XDeclaration("1.0", "utf-8", "no"),
new XComment("Reference a stylesheet"),
styleInstruction,
docType,
root
);
string tempPath = Path.Combine(Path.GetTempPath(), "sample.html");
doc.Save(tempPath);
Process.Start(tempPath); // This will display the page in IE or FireFox
File.ReadAllText(tempPath).Dump();
doc.Root.Name.LocalName.Dump("Root element's local name");
XElement bodyNode = doc.Root.Element(ns + "body");
(bodyNode.Document == doc).Dump("bodyNode.Document == doc");
(doc.Root.Parent == null).Dump("doc.Root.Parent is null");
foreach (XNode node in doc.Nodes())
{
Console.Write(node.Parent == null);
}
}
// Declarations 声明
{
var doc =
new XDocument(
new XDeclaration("1.0", "utf-16", "yes"),
new XElement("test", "data")
);
string tempPath = Path.Combine(Path.GetTempPath(), "test.xml");
doc.Save(tempPath);
File.ReadAllText(tempPath).Dump();
var output = new StringBuilder();
var settings = new XmlWriterSettings {
Indent = true
};
using (XmlWriter xw = XmlWriter.Create(output, settings))
doc.Save(xw);
output.ToString().Dump("Notice the encoding is utf-16 and not utf-8");
}
// Names and Namespaces 名称和命名空间
{
// 直接使用 {}
new XElement("{http://domain.com/xmlspace}customer", "Bloggs");
// 使用 XName 和 XNamespace
XName localName = "customer";
localName.Dump("localName");
XName fullName1 = "{http://domain.com/xmlspace}customer";
fullName1.Dump("fullname1");
XNamespace ns = "http://domain.com/xmlspace";
XName fullName2 = ns + "customer";
fullName2.Dump("fullname2 - same result, but cleaner and more efficient");
var data =
new XElement(ns + "data",
new XAttribute(ns + "id", 123)
);
data.Dump();
XElement x = data.Element(ns + "customer"); // OK
XElement y = data.Element("customer"); // null
// 为每一个元素分配命名空间
var data2 =
new XElement(ns + "data",
new XElement("customer", "Bloggs"),
new XElement("purchase", "Bicycle")
);
data.Dump("Before");
foreach (XElement e in data2.DescendantsAndSelf())
{
if (e.Name.Namespace == "")
{
e.Name = ns + e.Name.LocalName;
}
}
data.Dump("After");
// Prefixes 前缀
XNamespace ns1 = "http://domain.com/space1";
XNamespace ns2 = "http://domain.com/space2";
var mix =
new XElement(ns1 + "data",
new XElement(ns2 + "element", "value"),
new XElement(ns2 + "element", "value"),
new XElement(ns2 + "element", "value")
);
mix.Dump("Without prefixes");
mix.SetAttributeValue(XNamespace.Xmlns + "ns1", ns1);
mix.SetAttributeValue(XNamespace.Xmlns + "ns2", ns2);
mix.Dump("With prefixes");
XNamespace xsi = "http://www.w3.org/2001/XMLSchema-instance";
var nil = new XAttribute(xsi + "nil", true);
var cust =
new XElement("customers",
new XAttribute(XNamespace.Xmlns + "xsi", xsi),
new XElement("customer",
new XElement("lastname", "Bloggs"),
new XElement("dob", nil),
new XElement("credit", nil)
)
);
cust.Dump();
}
}
#elif true
// Annotations 注解
{
#if true
{
XElement e = new XElement("test");
e.AddAnnotation("Hello");
e.Annotation <string>().Dump("String annotations");
e.RemoveAnnotations <string>();
e.Annotation <string>().Dump("String annotations");
}
{
XElement e = new XElement("test");
e.AddAnnotation(new Customer {
ID = 13, Name = "Linaggan", Purchase = null
});
e.Annotations <Customer>().First().Name.Dump();
e.RemoveAnnotations <Customer>();
e.Annotations <Customer>().Count();
}
#endif
}
// Projecting into an X-DOM 将数据映射到X-DOM中
{
var customers =
new XElement("Customers",
new XElement("Customer", new XAttribute("id", 13),
new XElement("name", "Lianggan13"),
new XElement("buys", 3)));
NutshellEntities dataContext = new NutshellEntities();
var customers2 =
new XElement("Customers",
from c in dataContext.Customer.ToList() // 注:此处 要有 ToList()
select new XElement("Customer", new XAttribute("id", c.ID),
new XElement("name", c.Name),
new XElement("buys", (c.Purchase.Count))));
{
IEnumerable <XElement> queryxe =
from c in dataContext.Customer
select new XElement("Customer", new XAttribute("id", c.ID),
new XElement("name", c.Name),
new XElement("buys", c.Purchase.Count));
//var customers3 = new XElement("Customers", queryxe.AsQueryable());
}
{
// 在查询的客户信息中还包含客户最近的高价购买记录的详细信息 （排除空元素）
IEnumerable <XElement> queryxe2 =
from c in dataContext.Customer
let lastBigBuy = (
from p in c.Purchase
where p.Price > 1000
orderby p.Date descending
select p
).FirstOrDefault()
select new XElement("Customer", new XAttribute("id", c.ID),
new XElement("name", c.Name),
new XElement("buys", c.Purchase.Count),
lastBigBuy == null ? null : // 客户没有lastBigBuy时，返回null，其内容自动被忽略
new XElement("LastBigBuy",
new XElement("Description", lastBigBuy.Description),
new XElement("Price", lastBigBuy.Price)
));
// var customers4 = new XElement("Customers", queryxe2);
}
// Transfer X-DOM 转换 X-DOM
// 获取项目文件中的文件信息
XElement project = XElement.Parse(@"
<Project DefaultTargets=""Build"" xmlns=""http://schemas.microsoft.com/developer/msbuild/2003"">
<PropertyGroup>
<Platform Condition="" '$(Platform)' == '' "">AnyCPU</Platform>
<ProductVersion>9.0.11209</ProductVersion>
</PropertyGroup>
<ItemGroup>
<Compile Include=""ObjectGraph.cs"" />
<Compile Include=""Program.cs"" />
<Compile Include=""Properties\AssemblyInfo.cs"" />
<Compile Include=""Tests\Aggregation.cs"" />
<Compile Include=""Tests\Advanced\RecursiveXml.cs"" />
</ItemGroup>
</Project>");
XNamespace ns = project.Name.Namespace;
var queryFiles =
new XElement("ProjectReport",
from complieItem in project.Elements(ns + "ItemGroup").Elements(ns + "Compile")
let include = complieItem.Attribute("Include")
where include != null
select new XElement("File", include.Value));
queryFiles.Save(Directory.GetCurrentDirectory() + "\\" + "Files.xml");
var paths =
from complieItem in project.Elements(ns + "ItemGroup").Elements(ns + "Compile")
let include = complieItem.Attribute("Include")
where include != null
select include.Value;
var queryFoderFiles = new XElement("ProjectReport", ExpandPaths(paths));
queryFoderFiles.Save(Directory.GetCurrentDirectory() + "\\" + "FoderFiles .xml");
}
#endif
Console.ReadKey();
}
static void Main(string[] args)
{
// 序列 --> 序列
{
// 筛选运算符
// where Take TakeWhile Skip SkipWhile Distinct
{
string[] names = { "Tom", "Dick", "Harry", "Mary", "Jay" };
var query = from n in names
where n.Length > 3
let u = n.ToUpper() // let:引入变量作用域
where u.EndsWith("Y")
select u;
var query2 = names.Where((n, i) => i % 2 == 0); // 索引筛选 仅适用本地查询
int[] numbers = { 3, 5, 2, 234, 4, 1 };
numbers.TakeWhile(n => n < 100);
numbers.SkipWhile(n => n < 100);
}
// 映射运算符
// Select SelectMany
{
{
// 返回 “我的文档” 下所有目录的描述，而每个子集合包含相应目录下的文件
string sampleDirectory = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
DirectoryInfo[] dirs = new DirectoryInfo(sampleDirectory).GetDirectories();
// 关联子查询：子查询引用外部查询对象
var query =
from d in dirs
where (d.Attributes & FileAttributes.System) == 0
select new
{
DirectoryName = d.FullName,
Created = d.CreationTime,
Files = from f in d.GetFiles() // 此处引用 外部 查询变量
where (f.Attributes & FileAttributes.Hidden) == 0
select new { FileName = f.Name, f.Length, }
};
// Here's how to enumerate the results manually:
foreach (var dirFiles in query)
{
Console.WriteLine("Directory: " + dirFiles.DirectoryName);
foreach (var file in dirFiles.Files)
{
Console.WriteLine(" " + file.FileName + "Len: " + file.Length);
}
}
NutshellEntities dataContext = new NutshellEntities();
// 检索每个客户的姓名及其 大额购买记录
// 外连接：不论客户有没有购买记录，所有的客户都会被查询出来
var query2 = from c in dataContext.Customer
select new
{
c.Name,
Purchases = from p in c.Purchase // 利用导航属性
where p.Price > 1000
select new { p.Description, p.Price }
};
// 内连接：只查询大额购买的客户，其他客户不会被查询出来、
var query3 = from c in dataContext.Customer
where c.Purchase.Any(p => p.Price > 1000) // 增加一个筛选条件
select new
{
c.Name,
Purchases = from p in c.Purchase // 利用导航属性
where p.Price > 1000
select new { p.Description, p.Price }
};
// 使用let 改进 内连接
var query4 = from c in dataContext.Customer
let highValueP = from p in c.Purchase
where p.Price > 1000
select new { p.Description, p.Price }
where highValueP.Any()
select new { c.Name, Purchases = highValueP };
// 映射自定义实体类: 将结果 映射为 【多层对象层次结构】
var query5 = from c in dataContext.Customer
select new MyCustomerEntity
{
Name = c.Name,
Purchases =
(
from p in c.Purchase
where p.Price > 1000
select new MyPurchaseEntity
{
Description = p.Description,
Price = p.Price
}
).ToList()
};
List <MyCustomerEntity> result = query5.ToList();
}
{
// SelectMany 返回平面结果集 Select返回层次化结果集
// 如果实体类为特定关系定义了关联属性，那么可以扩展该子集合（非筛选交叉连接），实现关联查询效果
string[] fullNames = { "Anne Williams", "John Fred Smith", "Sue Green" };
var query1 = fullNames.SelectMany(n => n.Split());
var query2 = fullNames.SelectMany(n => n.Split().Select(n2 => new { n2, n }));
var query3 = fullNames.SelectMany(n => n.Split(), (n, n2) => new { n, n2 });
IEnumerable <string> query4 =
from fullName in fullNames
from x in fullName.Split().Select(name => new { name, fullName })
orderby x.fullName, x.name
select x.name + " came from " + x.fullName;
IEnumerable <string> query5 = fullNames
.SelectMany(fName => fName.Split().Select(name => new { name, fName }))
.OrderBy(x => x.fName)
.ThenBy(x => x.name)
.Select(x => x.name + " came from " + x.fName);
// 在 LINQ to SQL 和 EF 中使用 “SelectMany”
var players = new[] { "Tom", "Jay", "Mary" }.AsQueryable();
IEnumerable <string> query6 =
from name1 in players
from name2 in players
where name1.CompareTo(name2) < 0
orderby name1, name2
select name1 + " vs " + name2;
NutshellEntities dataContext = new NutshellEntities();
// 内连接
var query7 = from c in dataContext.Customer
from p in c.Purchase
where p.Price > 1000
from pi in p.PurchaseItem
select new { c.Name, p.Description, p.Price, pi.Detail };
// 外连接
var query8 = from c in dataContext.Customer
from p in c.Purchase.Where(p => p.Price > 1000).DefaultIfEmpty()
//from pi in p.PurchaseItem.DefaultIfEmpty()
select new
{
c.Name,
Description = p == null ? null : p.Description,
Price = p == null ? (decimal?)null : p.Price,
// Detail = pi == null ? null : pi.Detail
};
}
}
// 连接运算符
// Join GroupJoin Zip
{
{
{
// Join GroupJoin 将两个输入序列连接为一个输出序列，Join 生成平面的输出，GroupJoin 产生层次化的输出
NutshellEntities dataContext = new NutshellEntities();
var query1 = from c in dataContext.Customer
join p in dataContext.Purchase
on c.ID equals p.CustomerID
select c.Name + " bought a " + p.Description;
Customer[] localCustomers = dataContext.Customer.ToArray(); // 转化到本地
Purchase[] localPurchases = dataContext.Purchase.ToArray();
// 【SelectMany】 vs. 【Join】
var slowQuery2 = from c in localCustomers
//from p in c.Purchase where c.ID == p.CustomerID
from p in localPurchases where c.ID == p.CustomerID
select c.Name + " bought a " + p.Description;
var fastQuery3 = from c in localCustomers // 外部序列 localCustomers
join p in localPurchases // 内部序列 localPurchases
on c.ID equals p.CustomerID
select c.Name + " bought a " + p.Description;
// Join 在流式语法中的使用
var query4 = localCustomers.Join(localPurchases,
c => c.ID,
p => p.CustomerID, // IDE 不会给出提示
(c, p) => new { c.Name, p.Description, p.Price }
);
var query5 = localCustomers.Join(localPurchases,
c => c.ID,
p => p.CustomerID,
(c, p) => new { c, p })
.OrderBy(x => x.p.Price)
.Select(x => x.c.Name + " bought a " + x.p.Description);
}
{
// GroupJoin (join + into) 返回外部元素分组的层次化结果结果
NutshellEntities dataContext = new NutshellEntities();
IEnumerable <IEnumerable <Purchase> > query1 =
from c in dataContext.Customer
join p in dataContext.Purchase
on c.ID equals p.CustomerID
into custPurchases
select custPurchases;
// 左外连接(层次)
var query2 =
from c in dataContext.Customer
join p in dataContext.Purchase
on c.ID equals p.CustomerID
into custPurchases
select new { CustName = c.Name, custPurchases };
// 内连接 查询仅有购买记录的客户
var query3 = from c in dataContext.Customer
join p in dataContext.Purchase.Where(p => p.Price > 1000)
on c.ID equals p.CustomerID
into custPurchases
where custPurchases.Any()
select new { CustName = c.Name, custPurchases };
// 左外连接(平面) DefaultIfEmpty 需要有允许为 null 的地方
var query4 = from c in dataContext.Customer
join p in dataContext.Purchase
on c.ID equals p.CustomerID
into custPurchases
from pg in custPurchases.DefaultIfEmpty()
select new
{
CustName = c.Name,
Description = (pg == null) ? null : pg.Description,
Price = (pg == null) ? (decimal?)null : pg.Price
};
// 连接查找表
// 将所有的购买记录都加载进查找表中
ILookup <int?, Purchase> purchLookup =
dataContext.Purchase.ToLookup(p => p.CustomerID, p => p);
var query5 = from c in dataContext.Customer
from p in purchLookup[c.ID]
select new { c.Name, p.Description, p.Price };
// + DefaultIfEmpty --> 外连接
var query6 = from c in dataContext.Customer
from p in purchLookup[c.ID].DefaultIfEmpty()
select new
{
CustName = c.Name,
Description = (p == null) ? null : p.Description,
Price = (p == null) ? (decimal?)null : p.Price
};
}
{
// Zip 同时枚举两个集合中的元素(像拉链一下)
int[] numbers = { 3, 5, 7 };
string[] words = { "three", "five", "seven", "none" };
IEnumerable <string> zip = numbers.Zip(words, (n, w) => n + "=" + w);
}
}
}
// 排序运算符
// Ordery ThenBy Reverse
{
var names = new[] { "Tom", "Dick", "Harry", "Mary", "Jay" }.AsQueryable();
// By length, then alphabetically
var query1 = names.OrderBy(s => s.Length).ThenBy(s => s);
// By length, then second character, then first character
var query2 = names.OrderBy(s => s.Length).ThenBy(s => s[1]).ThenBy(s => s[0]);
var query3 =
from s in names
orderby s.Length, s[1], s[0]
select s;
NutshellEntities dataContext = new NutshellEntities();
var query4 = dataContext.Purchase
.OrderByDescending(p => p.Price)
.ThenBy(p => p.Description);
var query5 = from p in dataContext.Purchase
orderby p.Price descending, p.Description
select p;
// IComparer
var query6 = names.OrderBy(n => n, StringComparer.CurrentCultureIgnoreCase);
var query7 =
from c in dataContext.Customer
orderby c.Name.ToUpper()
select c.Name;
// IOrderedEnumerable IOrderedQueryable
IOrderedEnumerable <string> query8 = names.AsEnumerable().OrderBy(s => s.Length);
IOrderedEnumerable <string> query9 = query8.ThenBy(s => s);
var query10 = names.OrderBy(s => s.Length).AsEnumerable();
query10 = query10.Where(n => n.Length > 3);
}
// 分组运算符
// GroupBy
{
string[] files = Directory.GetFiles(Path.GetTempPath()).Take(100).ToArray();
IEnumerable <IGrouping <string, string> > query1 =
files.GroupBy(file => Path.GetExtension(file));
foreach (IGrouping <string, string> grouping in query1)
{
Console.WriteLine("Extension: " + grouping.Key);
foreach (string filename in grouping)
{
Console.WriteLine(" - " + filename);
}
}
// 指定 elementSelector 参数对输入元素处理，但与 排序主键选择器 keySelector 无关
var query2 = files.GroupBy(file => Path.GetExtension(file), file => file.ToUpper());
var query3 = from file in files
group file.ToUpper() by Path.GetExtension(file);
// + into --> 对分组结果 筛选
var query4 = from file in files
group file.ToUpper() by Path.GetExtension(file)
into grouping
where grouping.Count() < 5
select grouping;
// 分组求和: 分组统计一年销售额
NutshellEntities dataContext = new NutshellEntities();
var query5 = from p in dataContext.Purchase
group p.Price by p.Date.Year
into salesByYear
select new
{
Year = salesByYear.Key,
TotalPrice = salesByYear.Sum()
};
// 对多个键进行分组
var query6 = from n in new[] { "Tom", "Dick", "Harry", "Mary", "Jay" }.AsQueryable()
group n by new
{
FirstLetter = n[0],
Length = n.Length
};
// The following groups purchases by year, then returns only those groups where
// the average purchase across the year was greater than $1000:
var query7 = from p in dataContext.Purchase
group p.Price by p.Date.Year into salesByYear
where salesByYear.Average(x => x) > 1000
select new
{
Year = salesByYear.Key,
TotalSales = salesByYear.Count(),
AvgSale = salesByYear.Average(),
TotalValue = salesByYear.Sum()
};
}
// 集合运算符
// Concat Union Intersect Except
{
int[] seq1 = { 1, 2, 3 }, seq2 = { 3, 4, 5 };
// 合集
IEnumerable <int> concat = seq1.Concat(seq2);
// 合集 不含共有
IEnumerable <int> union = seq1.Union(seq2);
// 交接
seq1.Intersect(seq2);
// 补集
seq1.Except(seq2);
seq2.Except(seq1);
var query1 = from s1 in seq1
where !seq2.Contains(s1)
select s1;
}
// 转换方方法：导入，导出
// OfType Cast , ToArray ToList ToDictionary ToLookup AsEnumerable AsQueryable
{
// Cast 兼容类型，抛异常 OfType 忽略不兼容类型
ArrayList classicList = new ArrayList();
classicList.AddRange(new int[] { 3, 4, 5 });
DateTime offender = DateTime.Now;
classicList.Add(offender);
IEnumerable <int>
ofTypeSequence = classicList.OfType <int>(),
castSequence = classicList.Cast <int>();
// ofTypeSequence.Dump("Notice that the offending DateTime element is missing");
try
{
castSequence.ToList();
}
catch (InvalidCastException ex)
{
// ex.Message.Dump("Notice what the offending DateTime element does to the Cast sequence");
}
}
}
// 序列 --> 元素或标量值
{
// 元素运算符
// Fisrt FirstOfDefault Last LastOfDefault Single SingleOrDefault ElementAt DefaultIfEmpty
{
// DefaultIfEmpty
// 输入序列为空时，返回一个default元素列表，否则返回原始输入序列
// 实现展平结果的外连接
}
// 聚合方法
// Aggregate Average Count LongCount Sum Max Min
{
// Average
// 查询返回了平均购买记录大于＄500的用户
NutshellEntities dataContext = new NutshellEntities();
var query1 = from c in dataContext.Customer
where c.Purchase.Average(p => p.Price) > 500
select c;
// Aggregate
int[] numbers = { 1, 2, 3, 4 };
int sum1 = numbers.Aggregate(0, (total, n) => total + n);
int sum2 = numbers.Select(n => n * n).Aggregate((total, n) => total + n);
}
// 量词运算符
// All Any Contains SequenceEqual
{
int[] numbers = { 1, 2, 3, 4 };
bool hasAThree = numbers.Contains(3);
bool hasABiggerThree = numbers.Any(n => n > 3);
NutshellEntities dataContext = new NutshellEntities();
IQueryable <Customer> query1 = dataContext.Customer.Where(c => c.Purchase.All(p => p.Price < 100));
var query2 = "Hello".Distinct();
query2.SequenceEqual("Helo");
}
}
// Void --> 序列
{
// 生成集合方法
// Empty Rnage Repeatxdd
{
int[][] numbers =
{
new int[] { 1, 2, 3 },
new int[] { 4, 5, 6 },
null // this null makes the query below fail.
};
IEnumerable <int> flatExp = numbers.SelectMany(innerArray => innerArray);
IEnumerable <int> flat = numbers.SelectMany(innerArray => innerArray ?? Enumerable.Empty <int>());
Enumerable.Range(5, 5);
Enumerable.Repeat(true, 3);
}
}
Console.ReadLine();
}
