Dapper是一个用于.NET的简单的对象映射，并且在速度上有着轻ORM之王的称号。
Dapper扩展IDbConnection，提供有用的扩展方法来查询数据库。
那么Dapper是怎样工作的呢？
总共三步：
- 创建一个IDbConnection对象
- 写一个语句来执行CRUD操作
- 传递语句作为Execute方法的一个参数
因为这篇文章主要是为了学习其中一些方法的使用，所以，这里不再叙述安装等的一些使用，有需要的同学可以参考：
1.Execute
Execute是可以被IDbConnection类型的任何对象调用的扩展方法。它可以执行一个命令一次或者很多次，并且返回受影响的行数。
这个方法可以用于执行：
- 存储过程(Stored Procedure)
- 插入语句(INSERT statement)
- 更新语句(UPDATE statement)
- 删除语句(DELETE statement)
下面的表格，展示了Execute方法的参数
这里给出一个实现代码的示例，其余部分直接在官网上的示例上面记录学习。
using Dapper;using System;using System.Data.SqlClient;using System.Runtime.Serialization;namespace Dapper_Demo{ public class Customer { public int ID { get; set; } public string Name { get; set; } public string About { get; set; } public DateTime UpdateDate { get; set; } } class Program { private static readonly string connectionString = @"Data Source = 127.0.0.1;Initial Catalog = DapperDemo;User Id = sa;Password = 111111;"; static void Main(string[] args) { Console.WriteLine("Hello World!"); var customer = new Customer { ID = 2, Name = "jack", About = "jack hh", UpdateDate = DateTime.Now }; var Insertsql = @"insert into Customer values(@ID,@Name,@About,@UpdateDate)"; using(var connection=new System.Data.SqlClient.SqlConnection(connectionString)) { var affectedRows = connection.Execute(Insertsql,customer); Console.WriteLine(affectedRows); } Console.ReadKey(); } }} 注意，在使用之前，可以nuget程序集引入Dapper和System.Data.SqlClient
下面的部分是官方代码记录学习。
1.1 执行存储过程
单次(Single)
执行一次存储过程
string sql = "Invoice_Insert";using (var connection = My.ConnectionFactory()){ var affectedRows = connection.Execute(sql, new {Kind = InvoiceKind.WebInvoice, Code = "Single_Insert_1"}, commandType: CommandType.StoredProcedure); My.Result.Show(affectedRows);} 多次(Many)
执行存储过程多次。数组列表中的每个对象执行一次
string sql = "Invoice_Insert";using (var connection = My.ConnectionFactory()){ var affectedRows = connection.Execute(sql, new[] { new {Kind = InvoiceKind.WebInvoice, Code = "Many_Insert_1"}, new {Kind = InvoiceKind.WebInvoice, Code = "Many_Insert_2"}, new {Kind = InvoiceKind.StoreInvoice, Code = "Many_Insert_3"} }, commandType: CommandType.StoredProcedure ); My.Result.Show(affectedRows);} 1.2 执行插入
单次(Single)
执行一次插入语句
string sql = "INSERT INTO Customers (CustomerName) Values (@CustomerName);";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var affectedRows = connection.Execute(sql, new {CustomerName = "Mark"}); Console.WriteLine(affectedRows); var customer = connection.Query ("Select * FROM CUSTOMERS WHERE CustomerName = 'Mark'").ToList(); FiddleHelper.WriteTable(customer);} 多次(Many)
执行多次插入语句。数组列表中的每个对象执行一次
string sql = "INSERT INTO Customers (CustomerName) Values (@CustomerName);";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ connection.Open(); var affectedRows = connection.Execute(sql, new[] { new {CustomerName = "John"}, new {CustomerName = "Andy"}, new {CustomerName = "Allan"} });Console.WriteLine(affectedRows); 1.3 执行更新
单次(Single)
执行一次更新语句
string sql = "UPDATE Categories SET Description = @Description WHERE CategoryID = @CategoryID;";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var affectedRows = connection.Execute(sql,new {CategoryID = 1, Description = "Soft drinks, coffees, teas, beers, mixed drinks, and ales"}); Console.WriteLine(affectedRows);} 多次(Many)
执行多次更新语句。数组列表中的每个对象执行一次
string sql = "UPDATE Categories SET Description = @Description WHERE CategoryID = @CategoryID;";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var affectedRows = connection.Execute(sql, new[] { new {CategoryID = 1, Description = "Soft drinks, coffees, teas, beers, mixed drinks, and ales"}, new {CategoryID = 4, Description = "Cheeses and butters etc."} });Console.WriteLine(affectedRows); 1.4 执行删除
单次(Single)
执行一次删除语句
string sql = "DELETE FROM Customers WHERE CustomerID = @CustomerID";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var affectedRows = connection.Execute(sql, new {CustomerID = 1}); Console.WriteLine(affectedRows);} 多次(Many)
执行多次删除语句。数组列表中的每个对象执行一次
string sql = "DELETE FROM OrderDetails WHERE OrderDetailID = @OrderDetailID";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var affectedRows = connection.Execute(sql, new[] { new {OrderDetailID = 1}, new {OrderDetailID = 2}, new {OrderDetailID = 3} });Console.WriteLine(affectedRows); 1.5 场景说明
对于上面的execute方法在执行少量数据时，比较合适；但是如果执行数据量太大，速度就会很慢，就不适用了。下面会有对于大数据量的操作方法。
下面给出使用excute在执行批量插入数据时的一些结果。
代码如下:
1 using Dapper; 2 using System; 3 using System.Collections.Generic; 4 using System.Data.SqlClient; 5 using System.Diagnostics; 6 using System.Runtime.Serialization; 7 8 namespace Dapper_Demo 9 {10 11 public class Customer12 {13 public int ID { get; set; }14 15 public string Name { get; set; }16 17 public string About { get; set; }18 19 public DateTime UpdateDate { get; set; }20 21 }22 class Program23 {24 private static readonly string connectionString = @"Data Source = 127.0.0.1;Initial Catalog = DapperDemo;User Id = sa;Password = 111111;";25 static void Main(string[] args)26 {27 Console.WriteLine("Hello World!");28 29 var list = new List ();30 for(int i = 0; i < 100; i++)31 {32 var customer = new Customer { ID = i, Name = "jack"+i, About = "jack hh"+i, UpdateDate = DateTime.Now };33 list.Add(customer);34 }35 36 37 var Insertsql = @"insert into Customer values(@ID,@Name,@About,@UpdateDate)";38 39 var stopWatch = new Stopwatch();40 stopWatch.Start();41 using(var connection=new System.Data.SqlClient.SqlConnection(connectionString))42 {43 var affectedRows = connection.Execute(Insertsql,list);44 Console.WriteLine(affectedRows);45 }46 stopWatch.Stop();47 Console.WriteLine("花费的时间：" + stopWatch.ElapsedMilliseconds);48 49 Console.ReadKey();50 }51 }52 } 插入100条数据
插入500条数据
插入1000条数据
可以看出当数据量逐渐增大时，execute方法就不太适用了。
2. Query
这个方法使用来执行查询和映射结果的。
它的结果可以映射到：
- Anonymous
- Strongly Typed
- Multi-Mapping（One to One）
- Multi-Mapping(One to Many)
- Multi-Type
可以执行的参数
2.1 Query Anonymous
Query方法可以执行原生 SQL 查询并且映射结果到动态集合
string sql = "SELECT TOP 10 * FROM OrderDetails";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var orderDetail = connection.Query(sql).FirstOrDefault(); FiddleHelper.WriteTable(orderDetail);} 2.2 Query Strongly Typed
Query方法可以执行原生 SQL 查询并且映射结果到强类型集合
string sql = "SELECT TOP 10 * FROM OrderDetails";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var orderDetails = connection.Query (sql).ToList(); Console.WriteLine(orderDetails.Count); FiddleHelper.WriteTable(orderDetails);} 2.3 Query Multi-Mapping（One to One）
Query方法可以执行原生 SQL 查询并且用一对一的关系映射结果到强类型集合
string sql = "SELECT * FROM Invoice AS A INNER JOIN InvoiceDetail AS B ON A.InvoiceID = B.InvoiceID;";using (var connection = My.ConnectionFactory()){ connection.Open(); var invoices = connection.Query ( sql, (invoice, invoiceDetail) => { invoice.InvoiceDetail = invoiceDetail; return invoice; }, splitOn: "InvoiceID") .Distinct() .ToList();} 2.4 Query Multi-Mapping (One to Many)
Query方法可以执行原生 SQL 查询并且用一对多的关系映射结果到强类型集合
string sql = "SELECT TOP 10 * FROM Orders AS A INNER JOIN OrderDetails AS B ON A.OrderID = B.OrderID;";using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools())){ var orderDictionary = new Dictionary (); var list = connection.Query ( sql, (order, orderDetail) => { Order orderEntry; if (!orderDictionary.TryGetValue(order.OrderID, out orderEntry)) { orderEntry = order; orderEntry.OrderDetails = new List (); orderDictionary.Add(orderEntry.OrderID, orderEntry); } orderEntry.OrderDetails.Add(orderDetail); return orderEntry; }, splitOn: "OrderID") .Distinct() .ToList(); Console.WriteLine(list.Count); FiddleHelper.WriteTable(list); FiddleHelper.WriteTable(list.First().OrderDetails);} 2.5 Query Multi-Type
Query方法可以执行原生 SQL 查询并且映射结果到有多个类型的集合
string sql = "SELECT * FROM Invoice;";using (var connection = My.ConnectionFactory()){ connection.Open(); var invoices = new List (); using (var reader = connection.ExecuteReader(sql)) { var storeInvoiceParser = reader.GetRowParser (); var webInvoiceParser = reader.GetRowParser (); while (reader.Read()) { Invoice invoice; switch ((InvoiceKind) reader.GetInt32(reader.GetOrdinal("Kind"))) { case InvoiceKind.StoreInvoice: invoice = storeInvoiceParser(reader); break; case InvoiceKind.WebInvoice: invoice = webInvoiceParser(reader); break; default: throw new Exception(ExceptionMessage.GeneralException); } invoices.Add(invoice); } } My.Result.Show(invoices);}