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。
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<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
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<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);
}
来源：oschina
链接：https://my.oschina.net/u/4338729/blog/3399648