更新

LinqStudy.Test/LinqToDataSet/DataSetDemo.cs

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+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace LinqStudy.Test.LinqToDataSet
+{
+    public class DataSetDemo
+    {
+    }
+}

LinqStudy.Test/LinqToDataSet/DataTableDemo.cs

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+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace LinqStudy.Test.LinqToDataSet
+{
+    public class DataTableDemo
+    {
+    }
+}

LinqStudy.Test/LinqToObject/WhereTest.cs

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+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Linq;
+using System.Linq.Expressions;
+
+using Xunit;
+
+namespace LinqStudy.Test.LinqToObject
+{
+    /// <summary>
+    /// where操作符：过滤查询条件
+    /// </summary>
+    public class WhereTest
+    {
+
+        [Fact]
+        public void Where_Test()
+        {
+            var Persons = new List<Person>()
+            {
+                new Person(){ Id=1,Name="zhangsan",Age=2},
+                new Person(){ Id =2,Name="lishi",Age=33}
+            };
+
+            var query = Persons.Where(p => p.Name.StartsWith("zhang"));
+            var age = query.FirstOrDefault()?.Age;
+
+            Assert.Equal(2, age);
+        }
+
+        [Fact]
+        public void Where_Argm_Test()
+        {
+            List<Person> Persons = null;
+
+            Action act = ()=> { Persons.Where(p => p.Name.StartsWith("zhang")); };
+
+            Assert.Throws<ArgumentNullException>(act);
+        }
+    }
+}

LinqStudy.Test/LinqToSQL/Readme.txt

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+
+Linq To SQL 与EF一起学习，不再单独列出。

LinqStudy.Test/LinqToXml/Person.xml

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+<?xml version="1.0" encoding="utf-8" ?> 

LinqStudy.Test/Util/StringUtil.cs

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+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace LinqStudy.Test.Util
+{
+    public static class StringUtil
+    {
+
+    }
+}

LinqStudy/Models/PersonEqual.cs

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+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace LinqStudy
+{
+    /// <summary>
+    /// Person自定义比较类
+    /// 各属性均同，则相等.有一个Null值则不相等。
+    /// </summary>
+    public class PersonEqual : IEqualityComparer<Person>
+    {
+        bool IEqualityComparer<Person>.Equals(Person x, Person y)
+        {
+            if (x==null || y==null)
+            {
+                return false;
+            }
+
+            return x.Id == y.Id && x.Name == y.Name && x.Age == y.Age;
+        }
+
+        int IEqualityComparer<Person>.GetHashCode(Person obj)
+        {
+            return (obj.Id+obj.Name+obj.Age).GetHashCode();
+        }
+    }
+}