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：https://dapper-tutorial.net/dapper
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。
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)
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<Customer>("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 Customer 12 { 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 Program 23 { 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<Customer>(); 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
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<OrderDetail>(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<Invoice, InvoiceDetail, Invoice>( 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<int, Order>(); var list = connection.Query<Order, OrderDetail, Order>( sql, (order, orderDetail) => { Order orderEntry; if (!orderDictionary.TryGetValue(order.OrderID, out orderEntry)) { orderEntry = order; orderEntry.OrderDetails = new List<OrderDetail>(); 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<Invoice>(); using (var reader = connection.ExecuteReader(sql)) { var storeInvoiceParser = reader.GetRowParser<StoreInvoice>(); var webInvoiceParser = reader.GetRowParser<WebInvoice>(); 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); } 3. QueryFirst
待续。。
来源：博客园
作者：Vincent-yuan
链接：https://www.cnblogs.com/Vincent-yuan/p/11504004.html