Dapper学习(一)之Execute和Query

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 = , 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 = , 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 = , Description = "Soft drinks, coffees, teas, beers, mixed drinks, and ales"},
    new {CategoryID = , 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 = });

    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 = },
    new {OrderDetailID = },
    new {OrderDetailID = }
    }
);

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:

 using Dapper;
 using System;
 using System.Collections.Generic;
 using System.Data.SqlClient;
 using System.Diagnostics;
 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 list = new List<Customer>();
             for(int i = ; i < ; i++)
             {
                 var customer = new Customer { ID = i, Name = "jack"+i, About = "jack hh"+i, UpdateDate = DateTime.Now };
                 list.Add(customer);
             }

             var Insertsql = @"insert into Customer values(@ID,@Name,@About,@UpdateDate)";

             var stopWatch = new Stopwatch();
             stopWatch.Start();
             using(var connection=new System.Data.SqlClient.SqlConnection(connectionString))
             {
                 var affectedRows = connection.Execute(Insertsql,list);
                 Console.WriteLine(affectedRows);
             }
             stopWatch.Stop();
             Console.WriteLine("花费的时间：" + stopWatch.ElapsedMilliseconds);

             Console.ReadKey();
         }
     }
 }

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);
}