背景介紹

在ADO.NET中我們可以根據用戶輸入的查詢條件拼接出指定的SQL語句進行查詢或者篩選出所需的數據，但是在ORM框架如EF中，我們一般用LINQ操作數據查詢，LINQ是否可以像SQL一樣拼接查詢條件呢？答案是可以的。這一技術叫Linq.Dynamic(動態Linq)，Linq.Dynamic的出現解決了本人心中的疑惑，不然總感覺少了什么。不管怎么樣，我們首先要做的是去網上找各種大神的資料，本文參考如下幾篇資料：

Linq.Dynamic基本介紹1：https://www.cnblogs.com/myzony/p/9143692.html

Linq.Dynamic基本介紹2：https://blog.csdn.net/flyingdream123/article/details/79962525

另外Linq.Dynamic是由外國大神所創，源碼在其個人主頁上也有：源碼地址

首先，需要在NuGet程序包中引入Linq.Dynamic.Core并引用其命名空間才能使用。

其次，使用動態查詢必須先調用AsQueryable()方法。

static void Main(string[] args){List<Phone> PhoneLists = new List<Phone>(){new Phone { Country = "中國", City = "北京", Name = "小米" },new Phone { Country = "中國",City = "北京",Name = "華為"},new Phone { Country = "中國",City = "北京",Name = "聯想"},new Phone { Country = "中國",City = "臺北",Name = "魅族"},new Phone { Country = "日本",City = "東京",Name = "索尼"},new Phone { Country = "日本",City = "大阪",Name = "夏普"},new Phone { Country = "日本",City = "東京",Name = "松下"},new Phone { Country = "美國",City = "加州",Name = "蘋果"},new Phone { Country = "美國",City = "華盛頓",Name = "三星"},new Phone { Country = "美國",City = "華盛頓",Name = "HTC"}};var Lists = PhoneLists.AsQueryable().Where("Country = @0 And City = @1", "中國", "北京").OrderBy("Name,City").Select("new (Country as Country,City as City,Name as Name)");var dLists = Lists.ToDynamicList();foreach (var list in dLists){Console.WriteLine(list.Country + "-" + list.City + "-" + list.Name);}Console.Read();}

運行效果如下圖所示：

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當然也支持GroupBy()查詢，代碼如下：

static void Main(string[] args){List<Phone> PhoneLists = new List<Phone>(){new Phone { Country = "中國", City = "北京", Name = "小米" },new Phone { Country = "中國",City = "北京",Name = "華為"},new Phone { Country = "中國",City = "北京",Name = "聯想"},new Phone { Country = "中國",City = "臺北",Name = "魅族"},new Phone { Country = "日本",City = "東京",Name = "索尼"},new Phone { Country = "日本",City = "大阪",Name = "夏普"},new Phone { Country = "日本",City = "東京",Name = "松下"},new Phone { Country = "美國",City = "加州",Name = "蘋果"},new Phone { Country = "美國",City = "華盛頓",Name = "三星"},new Phone { Country = "美國",City = "華盛頓",Name = "HTC"}};var Lists = PhoneLists.AsQueryable().GroupBy("new (Country as Country,City as City)");var dLists = Lists.ToDynamicList();foreach (var list in dLists){Console.WriteLine(list + ":");foreach (var lis in list){Console.WriteLine(lis.Country + "-" + lis.City + "-" + lis.Name);Console.WriteLine($"{lis.Country} - {lis.City} - {lis.Name}");}}Console.Read();}

執行效果如下圖所示：

希望對大家有所幫助！

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