視頻演示：http://u.115.com/file/f2cf72dc9e

也許最常用的查詢操作是應用布爾表達式形式的篩選器。此篩選器使查詢只返回那些表達式結果為 true 的元素。使用 where 子句生成結果。實際上，篩選器指定從源序列中排除哪些元素。在下面的示例中，只返回那些地址位于倫敦的 customers。

NorthwindDataContext db = new NorthwindDataContext(); var LondonCustomers = from Customer in db.Customers where Customer.City == "London" select Customer; foreach (var Customer in LondonCustomers) { Console.WriteLine("---------------------"); Console.WriteLine("Customer ID : {0}", Customer.CustomerID); Console.WriteLine("Customer Name : {0}", Customer.ContactName); Console.WriteLine("City : {0}", Customer.City); } NorthwindDataContext db = new NorthwindDataContext();var LondonCustomers = from Customer in db.Customerswhere Customer.City == "London"select Customer;foreach (var Customer in LondonCustomers) {Console.WriteLine("---------------------");Console.WriteLine("Customer ID : {0}", Customer.CustomerID);Console.WriteLine("Customer Name : {0}", Customer.ContactName);Console.WriteLine("City : {0}", Customer.City); }

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您可以使用熟悉的 C# 邏輯 AND 和 OR 運算符來根據需要在 where 子句中應用任意數量的篩選表達式。例如，若要只返回位于“倫敦”AND 姓名為“Thomas Hardy”的客戶，您應編寫下面的代碼：

var LondonCustomers = from Customer in db.Customers where Customer.City == "London" && Customer.ContactName == "Thomas Hardy" select Customer; var LondonCustomers = from Customer in db.Customerswhere Customer.City == "London" && Customer.ContactName == "Thomas Hardy"select Customer;

若要返回位于倫敦或巴黎的客戶，您應編寫下面的代碼：

var LondonCustomers = from Customer in db.Customers where Customer.City == "London" || Customer.City == "Paris" select Customer;

轉載于:https://www.cnblogs.com/GJYSK/archive/2010/10/28/1863789.html

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