From 6e181771a2779100a000f7ae99304d2a721ebce1 Mon Sep 17 00:00:00 2001
From: bicijinlian <bicijinlian@163.com>
Date: Sat, 31 Aug 2019 17:51:44 +0800
Subject: [PATCH] =?UTF-8?q?=E6=9B=B4=E6=96=B0?=
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LinqStudy.Test/Doc/LinqToObject.md | 43 +++++
LinqStudy.Test/Doc/Linq总体说明.md | 1 +
LinqStudy.Test/LinqBase/Lamda表达式.md | 1 +
LinqStudy.Test/LinqBase/初始化器.md | 1 +
.../LinqBase/匿名类与匿名方法.md | 1 +
LinqStudy.Test/LinqToObject/BaseTest.cs | 96 ++++++++++
LinqStudy.Test/LinqToObject/CreateTest.cs | 11 ++
LinqStudy.Test/LinqToObject/OtherTest.cs | 30 ++++
LinqStudy.Test/LinqToObject/ProjectiveTest.cs | 168 ++++++++++++++++++
LinqStudy/Models/Employee.cs | 16 ++
10 files changed, 368 insertions(+)
create mode 100644 LinqStudy.Test/Doc/LinqToObject.md
create mode 100644 LinqStudy.Test/Doc/Linq总体说明.md
create mode 100644 LinqStudy.Test/LinqBase/Lamda表达式.md
create mode 100644 LinqStudy.Test/LinqBase/初始化器.md
create mode 100644 LinqStudy.Test/LinqBase/匿名类与匿名方法.md
create mode 100644 LinqStudy.Test/LinqToObject/BaseTest.cs
create mode 100644 LinqStudy.Test/LinqToObject/CreateTest.cs
create mode 100644 LinqStudy.Test/LinqToObject/OtherTest.cs
create mode 100644 LinqStudy.Test/LinqToObject/ProjectiveTest.cs
create mode 100644 LinqStudy/Models/Employee.cs
diff --git a/LinqStudy.Test/Doc/LinqToObject.md b/LinqStudy.Test/Doc/LinqToObject.md
new file mode 100644
index 0000000..b9ffe14
--- /dev/null
+++ b/LinqStudy.Test/Doc/LinqToObject.md
@@ -0,0 +1,43 @@
+# Linq To Object
+
+> Linq To Object是操作内存对象。
+>
+> 使用前提：对象必须实现IEnumerable或`IEnumerable<T>`接口。
+>
+> 因为IQueryable和`IQueryable<T>`也实现了IEnumerable或`IEnumerable<T>接口`，所以也可以使用Linq To Object。
+> 泛型集合均实现了`IEnumerable<T>`接口，可以直接使用。
+> 一些集合类，也提供了转换扩展方法，可以转换后使用。
+>
+
+## Linq To Object本质
+
+> 本质是扩展方法，没有相应的 Linq Provider，这点与 Linq To SQL不同。
+
+## 注意事项
+
++ 延时执行
+
+ > 写好操作步骤时，只是进行了“定义”，直到调用(转换方法、聚合方法会立即执行)时才会真正执行操作。这点特别注意。
+
++ 异常
+
+ > 当对象为null时，通常都会抛出“参数null值”异常。使用前，就确保对象不为null
+
+ ``` csharp
+ [Fact]
+ public void Null_Test()
+ {
+ List<Person> person = null;
+
+ //对Linq操作符而言，基本上数据源为Null时，将引发异常。
+ Assert.ThrowsAny<ArgumentNullException>(() =>
+ {
+ //此处引发异常
+ var query = person.Where(p => p == null);
+ });
+ }
+ ```
+
++ 操作结果
+
+ > 当操作结果没有数据项时，不是返回null,而是返回“0数据项”的IEnumerable对象。对结果**不用进行null值判断**
diff --git a/LinqStudy.Test/Doc/Linq总体说明.md b/LinqStudy.Test/Doc/Linq总体说明.md
new file mode 100644
index 0000000..97b38ca
--- /dev/null
+++ b/LinqStudy.Test/Doc/Linq总体说明.md
@@ -0,0 +1 @@
+# Linq总体说明
diff --git a/LinqStudy.Test/LinqBase/Lamda表达式.md b/LinqStudy.Test/LinqBase/Lamda表达式.md
new file mode 100644
index 0000000..b124f4b
--- /dev/null
+++ b/LinqStudy.Test/LinqBase/Lamda表达式.md
@@ -0,0 +1 @@
+# Markdown file
\ No newline at end of file
diff --git a/LinqStudy.Test/LinqBase/初始化器.md b/LinqStudy.Test/LinqBase/初始化器.md
new file mode 100644
index 0000000..b124f4b
--- /dev/null
+++ b/LinqStudy.Test/LinqBase/初始化器.md
@@ -0,0 +1 @@
+# Markdown file
\ No newline at end of file
diff --git a/LinqStudy.Test/LinqBase/匿名类与匿名方法.md b/LinqStudy.Test/LinqBase/匿名类与匿名方法.md
new file mode 100644
index 0000000..b124f4b
--- /dev/null
+++ b/LinqStudy.Test/LinqBase/匿名类与匿名方法.md
@@ -0,0 +1 @@
+# Markdown file
\ No newline at end of file
diff --git a/LinqStudy.Test/LinqToObject/BaseTest.cs b/LinqStudy.Test/LinqToObject/BaseTest.cs
new file mode 100644
index 0000000..18b8b3d
--- /dev/null
+++ b/LinqStudy.Test/LinqToObject/BaseTest.cs
@@ -0,0 +1,96 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Linq;
+using System.Linq.Expressions;
+using FluentAssertions;
+
+using Xunit;
+
+namespace LinqStudy.Test.LinqToObject
+{
+ /// <summary>
+ /// 基本项测试
+ /// </summary>
+ public class BaseTest
+ {
+ /// <summary>
+ /// 数据源为 Null,引发异常.
+ /// </summary>
+ /// <exception cref="ArgumentNullException">
+ /// ArgumentNullException
+ /// </exception>
+ /// <remarks>
+ /// 对Linq操作符而言，数据源为Null时，均引发异常。
+ /// </remarks>
+ [Fact]
+ public void DataSource_IsNull_Test()
+ {
+ List<Person> person = null;
+
+ Assert.ThrowsAny<ArgumentNullException>(() =>
+ {
+ //引发异常
+ var query = person.Where(p => p == null);
+ });
+ }
+
+ /// <summary>
+ /// 数据源数据项为0时,不会引发异常.
+ /// </summary>
+ [Fact]
+ public void DataSource_Item_0_Test()
+ {
+ List<Person> person = new List<Person>();
+
+ //数据源为没有任何内容项时，即 Count=0，不会引发异常。
+ Action action = () =>
+ {
+ //查不到任何数据，不返回null，而是返回 Count=0的对象。
+ person.Where(p => p == null).ToList();
+ };
+
+ //不引发异常
+ action.Should().NotThrow();
+ }
+
+ /// <summary>
+ /// 数据源数据项为0时，查询等操作，不返回null,而返回“0数据项的”IEnumerable<T>对象。
+ /// </summary>
+ [Fact]
+ public void DataSource_Item0_Return_Test()
+ {
+ List<Person> person = new List<Person>();
+
+ //数据源为没有任何内容项时，即 Count=0，不会引发异常。
+ Action action = () =>
+ {
+ //查不到任何数据，不返回null，而是返回 Count=0的对象。
+ person.Where(p => p == null).ToList();
+ };
+
+ //不引发异常
+ action.Should().NotThrow();
+ }
+
+ /// <summary>
+ /// 查询不到数据项时，不返回null,而是返回“0数据项的”IEnumerable<T>对象
+ /// </summary>
+ [Fact]
+ public void NoQueryItem_Return_Test()
+ {
+ List<Person> person = new List<Person>()
+ {
+ new Person(){ Id=1,Name="小屁孩",Age=87},
+ new Person(){ Id=2,Name="小屁孩",Age=45},
+ new Person(){ Id=3,Name="小屁孩",Age=55},
+ new Person(){ Id=4,Name="小屁孩",Age=23},
+ };
+
+ //查不到数据时，返回Count=0的IEnumerable<T>对象
+ var result = person.Where(p => p.Age < 10).ToList();
+
+ Assert.Empty(result);
+ }
+ }
+}
diff --git a/LinqStudy.Test/LinqToObject/CreateTest.cs b/LinqStudy.Test/LinqToObject/CreateTest.cs
new file mode 100644
index 0000000..0aaacc5
--- /dev/null
+++ b/LinqStudy.Test/LinqToObject/CreateTest.cs
@@ -0,0 +1,11 @@
+using System;
+
+namespace LinqStudy.Test.LinqToObject
+{
+ /// <summary>
+ /// 生成操作符
+ /// </summary>
+ public class CreateTest
+ {
+ }
+}
diff --git a/LinqStudy.Test/LinqToObject/OtherTest.cs b/LinqStudy.Test/LinqToObject/OtherTest.cs
new file mode 100644
index 0000000..b7285b1
--- /dev/null
+++ b/LinqStudy.Test/LinqToObject/OtherTest.cs
@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Xunit;
+namespace LinqStudy.Test.LinqToObject
+{
+ public class OtherTest
+ {
+ /// <summary>
+ /// is操作符用作if条件时，判断之后可以直接赋值给一个变量.(输出给变量)
+ /// 其它地方可以用as实现相同功能
+ /// </summary>
+ /// <example>
+ /// if (id is List-int output){output.Add(1);}
+ /// </example>
+ [Fact]
+ public void Is_Test()
+ {
+ List<int> id = new List<int>();
+
+ if (id is List<int> output)
+ {
+ output.Add(1);
+ }
+
+ var cc = id as List<int>;
+ cc.Add(1);
+ }
+ }
+}
diff --git a/LinqStudy.Test/LinqToObject/ProjectiveTest.cs b/LinqStudy.Test/LinqToObject/ProjectiveTest.cs
new file mode 100644
index 0000000..0386b74
--- /dev/null
+++ b/LinqStudy.Test/LinqToObject/ProjectiveTest.cs
@@ -0,0 +1,168 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+
+using Xunit;
+
+using LinqStudy;
+
+namespace LinqStudy.Test.LinqToObject
+{
+ /// <summary>
+ /// 投影操作符
+ /// 投影：遍历序列中的元素，将元素由一种类型转换为另一种类型的操作，并返回由转换后元素组成的新序列。
+ /// 即是：IEnumerable<TSource> => IEnumerable<TResult>
+ /// </summary>
+ public class ProjectiveTest
+ {
+ /// <summary>
+ /// Select投影：简单投影，一对一
+ /// </summary>
+ [Fact]
+ public void Select_Test()
+ {
+ // Arrange
+ var persons = PersonManager.GetPersons();
+
+ // Act
+ var maps = persons.Select(p=>p.Age).ToList();
+
+ // Assert
+ Assert.IsType<List<int>>(maps);
+ }
+ /// <summary>
+ /// 投影为匿名类
+ /// </summary>
+ [Fact]
+ public void Select_Anonymous_Test()
+ {
+ // Arrange
+ var persons = PersonManager.GetPersons();
+
+ // Act
+ var maps = persons.Select(p=>new {Id=p.Id, Node=$"姓名{p.Name},年龄{p.Age}."}).ToList();
+
+ // Assert
+ Assert.IsNotType<List<Person>>(maps);
+ }
+
+ /// <summary>
+ /// 投影传入索引(序号)参数
+ /// </summary>
+ [Fact]
+ public void Select_Index_Test()
+ {
+ var persons = PersonManager.GetPersons();
+
+ var maps = persons.Select((query,index)=> new KeyValuePair<int, Person>(index,query)).ToList();
+ var indexs = persons.Select((query, index) => index).ToList();
+
+ Assert.IsType<List<KeyValuePair<int, Person>>>(maps);
+ Assert.Equal(0,indexs[0]);
+ }
+
+ /// <summary>
+ /// SelectMany:复合投影，一对多，合并多到一个集合。
+ /// 枚举源序列，将源序列每一项投影为新的集合，合并所有新集合为一个可枚举序列，做为返回值；
+ /// 提供了将多个 from子句组合起来的功能，它将每个对象的结果合并成单个可枚举序列。
+ /// </summary>
+ [Fact]
+ public void SelectMany_Test()
+ {
+ var employees = new List<Employee>()
+ {
+ new Employee(){Id=1,Name="小明",Emails=new List<string>(){ "abc@163.com", "acd@163.com", "ade@163.com" } },
+ new Employee(){Id=2,Name="大壮",Emails=new List<string>(){ "bbc@163.com", "bcd@163.com", "bde@163.com" } },
+ new Employee(){Id=3,Name="周羊",Emails=new List<string>(){ "cbc@163.com", "ccd@163.com", "cde@163.com" } },
+ new Employee(){Id=4,Name="承承",Emails=new List<string>(){ "dbc@163.com", "dcd@163.com", "dde@163.com" } },
+ new Employee(){Id=5,Name="东升",Emails=new List<string>(){ "ebc@163.com", "ecd@163.com", "ede@163.com" }},
+ };
+
+ var maps = employees.SelectMany(q=>q.Emails).ToList();
+
+ Assert.IsType<List<string>>(maps);
+ Assert.Equal(15, maps.Count);
+ }
+
+ /// <summary>
+ /// 投影传入索引(序号)参数
+ /// </summary>
+ [Fact]
+ public void SelectMany_Index_Test()
+ {
+ var employees = new List<Employee>()
+ {
+ new Employee(){Id=1,Name="小明",Emails=new List<string>(){ "abc@163.com", "acd@163.com", "ade@163.com" } },
+ new Employee(){Id=2,Name="大壮",Emails=new List<string>(){ "bbc@163.com", "bcd@163.com", "bde@163.com" } },
+ new Employee(){Id=3,Name="周羊",Emails=new List<string>(){ "cbc@163.com", "ccd@163.com", "cde@163.com" } },
+ new Employee(){Id=4,Name="承承",Emails=new List<string>(){ "dbc@163.com", "dcd@163.com", "dde@163.com" } },
+ new Employee(){Id=5,Name="东升",Emails=new List<string>(){ "ebc@163.com", "ecd@163.com", "ede@163.com" }},
+ };
+
+ var maps = employees.SelectMany((q, idx) =>
+ {
+ q.Emails.Add(idx.ToString());
+ return q.Emails;
+ }).ToList();
+
+ Assert.IsType<List<string>>(maps);
+ Assert.Equal(20, maps.Count);
+ }
+
+ /// <summary>
+ /// 自定义结果项:源项与源项选择的集合项，一一组合，组成新自定义序列。
+ /// 类似Cross JOIN
+ /// </summary>
+ [Fact]
+ public void SelectMany_TCollection_Test()
+ {
+ var employees = new List<Employee>()
+ {
+ new Employee(){ Id=1,Name="小明",Emails=new List<string>(){ "a1@163.com", "a2@163.com", "a3@163.com" } },
+ new Employee(){ Id=2,Name="大壮",Emails=new List<string>(){ "b1@163.com", "b2@163.com", "b3@163.com" } },
+ new Employee(){ Id=3,Name="周羊",Emails=new List<string>(){ "c1@163.com", "c2@163.com", "c3@163.com" } },
+ new Employee(){ Id=4,Name="承承",Emails=new List<string>(){ "d1@163.com", "d2@163.com", "d3@163.com" } },
+ new Employee(){ Id=5,Name="东升",Emails=new List<string>(){ "e1@163.com", "e2@163.com", "e3@163.com" } },
+ };
+
+ var maps = employees.SelectMany((employee)=> employee.Emails,(person,email)=> new { Name=person.Name,Email=email}).ToList();
+
+ Assert.Equal(15, maps.Count);
+ }
+
+ /// <summary>
+ /// 自定义结果项:带索引
+ /// 类似Cross JOIN
+ /// </summary>
+ [Fact]
+ public void SelectMany_TCollection_Index_Test()
+ {
+ var employees = new List<Employee>()
+ {
+ new Employee(){ Id=1,Name="小明",Emails=new List<string>(){ "a1@163.com", "a2@163.com", "a3@163.com" } },
+ new Employee(){ Id=2,Name="大壮",Emails=new List<string>(){ "b1@163.com", "b2@163.com", "b3@163.com" } },
+ new Employee(){ Id=3,Name="周羊",Emails=new List<string>(){ "c1@163.com", "c2@163.com", "c3@163.com" } },
+ new Employee(){ Id=4,Name="承承",Emails=new List<string>(){ "d1@163.com", "d2@163.com", "d3@163.com" } },
+ new Employee(){ Id=5,Name="东升",Emails=new List<string>(){ "e1@163.com", "e2@163.com", "e3@163.com" } },
+ };
+
+ var maps = employees.SelectMany
+ (
+ (employee, idx) =>
+ {
+ return new List<Employee>() { new Employee() { Id = employee.Id, Name = employee.Name + "_" + idx, Emails = employee.Emails } };
+ },
+
+ (person,email) => new
+ {
+ Name = email.Name,
+ Email = email.Emails
+ }
+ )
+ .ToList();
+
+ Assert.Equal(5, maps.Count);
+ }
+ }
+}
diff --git a/LinqStudy/Models/Employee.cs b/LinqStudy/Models/Employee.cs
new file mode 100644
index 0000000..1db3c25
--- /dev/null
+++ b/LinqStudy/Models/Employee.cs
@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace LinqStudy
+{
+ /// <summary>
+ /// 雇员
+ /// </summary>
+ public class Employee
+ {
+ public int Id { get; set; }
+ public string Name { get; set; }
+ public List<string> Emails { get; set; }
+ }
+}