Dapper是什么？

　　Dpper是一款.Net平台简单（Simple）的对象映射库，并且Dapper拥有着“微型ORM之王”的称号。就速度而言与手写ADO.NET SqlDateReader相同。ORM是Object Relational Mapper的缩写，代表着数据库与编程语言之间的映射。

　　Dapper的基本特性是通过扩展IDbConnection 接口，并为其提供查询数据库的方法。

Dapper是如何工作的？

　　将大象装冰箱总共分三步，Dapper也是如此。

创建IDBConnection对象（例如：SqlConnection）
编写用于CRUD的Sql语句
将Sql语句当作参数纯如执行操作的方法

安装

　　通过NuGet安装：https://www.nuget.org/packages/Dapper

　　PM> Install-Package Dapper

方法表

　　Dapper会用多个方法去扩展IDBConnection接口

Execute
Query
QueryFirst
QueryFirstOrDefault
QuerySingle
QuerySingleOrDefault
QueryMultiple

string sqlInvoices = "SELECT * FROM Invoice;";
string sqlInvoice = "SELECT * FROM Invoice WHERE InvoiceID = @InvoiceID;";
string sp = "EXEC Invoice_Insert";

using (var connection = My.ConnectionFactory())
{
    var invoices = connection.Query<Invoice>(sqlInvoices).ToList();
    var invoice = connection.QueryFirstOrDefault(sqlInvoice, new {InvoiceID = 1});
    var affectedRows = connection.Execute(sp, new { Param1 = "Single_Insert_1" }, commandType: CommandType.StoredProcedure);
}

参数表

　　有多种不同的方式给“查询（例如：select）”和“执行（例如：delete、update、insert）”方法传递参数

Anonymous
Dynamic
List
String

// 匿名类对象（相对比较常用）
var affectedRows = connection.Execute(sql,
                    new {Kind = InvoiceKind.WebInvoice, Code = "Single_Insert_1"},
                    commandType: CommandType.StoredProcedure);

// Dynamic
DynamicParameters parameter = new DynamicParameters();

parameter.Add("@Kind", InvoiceKind.WebInvoice, DbType.Int32, ParameterDirection.Input);
parameter.Add("@Code", "Many_Insert_0", DbType.String, ParameterDirection.Input);
parameter.Add("@RowCount", dbType: DbType.Int32, direction: ParameterDirection.ReturnValue);

connection.Execute(sql,
    new {Kind = InvoiceKind.WebInvoice, Code = "Single_Insert_1"},
    commandType: CommandType.StoredProcedure);

// List
connection.Query<Invoice>(sql, new {Kind = new[] {InvoiceKind.StoreInvoice, InvoiceKind.WebInvoice}}).ToList();

// String
connection.Query<Invoice>(sql, new {Code = new DbString {Value = "Invoice_1", IsFixedLength = false, Length = 9, IsAnsi = true}}).ToList();

结果集

　　查询方法的返回值可以映射成多种类型

Anonymous
Strongly Typed
Multi-Mapping
Multi-Result
Multi-Type

string sql = "SELECT * FROM Invoice;";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var anonymousList = connection.Query(sql).ToList();
    var invoices = connection.Query<Invoice>(sql).ToList();
}

Utilities

Async
Buffered
Transaction
Stored Procedure

// Async
connection.QueryAsync<Invoice>(sql)

// Buffered
connection.Query<Invoice>(sql, buffered: false)

// Transaction
using (var transaction = connection.BeginTransaction())
{
    var affectedRows = connection.Execute(sql,
        new {Kind = InvoiceKind.WebInvoice, Code = "Single_Insert_1"},
        commandType: CommandType.StoredProcedure,
        transaction: transaction);

    transaction.Commit();
}

// Stored Procedure
var affectedRows = connection.Execute(sql,
    new {Kind = InvoiceKind.WebInvoice, Code = "Single_Insert_1"},
    commandType: CommandType.StoredProcedure);

执行非查询语句

描述

你可以从任意实现IDbConnection的类对象中调用Dapper的扩展方法“Execute”。它能够执行一条命令（Command）一次或者多次，并返回受影响的行数。这个方法通常用来执行：

Stored Procedure
INSERT statement
UPDATE statement
DELETE statement

参数

下面表格中显示了Execute方法的不同参数

名称	描述
sql	要执行的sql语句文本
param	command的参数
transaction	事务
commandTimeout	command超时时间
commandType	command类型

示例：执行存储过程

单次

执行存储过程一次

string sql = "EXEC Invoice_Insert";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var affectedRows = connection.Execute(sql,
        new {Kind = InvoiceKind.WebInvoice, Code = "Single_Insert_1"},
        commandType: CommandType.StoredProcedure);

    My.Result.Show(affectedRows);
}

多次

执行存储过程多次，数组中的每条数据都执行一次

string sql = "EXEC Invoice_Insert";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    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);
}

示例：执行插入

单次

执行插入语句一次

string sql = "INSERT INTO Invoice (Code) Values (@Code);";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var affectedRows = connection.Execute(sql, new {Kind = InvoiceKind.WebInvoice, Code = "Single_Insert_1"});

    My.Result.Show(affectedRows);
}

多次

执行多次，数组中的每条数据都执行一次

string sql = "INSERT INTO Invoice (Code) Values (@Code);";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    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"}
        }
    );

    My.Result.Show(affectedRows);
}

示例：执行Update

单次

执行Update语句一次

string sql = "UPDATE Invoice SET Code = @Code WHERE InvoiceID = @InvoiceID";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var affectedRows = connection.Execute(sql, new {InvoiceID = 1, Code = "Single_Update_1"});

    My.Result.Show(affectedRows);
}

多次

执行多次，数组中的每条数据都执行一次。

string sql = "UPDATE Invoice SET Code = @Code WHERE InvoiceID = @InvoiceID";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var affectedRows = connection.Execute(sql,
        new[]
        {
            new {InvoiceID = 1, Code = "Many_Update_1"},
            new {InvoiceID = 2, Code = "Many_Update_2"},
            new {InvoiceID = 3, Code = "Many_Update_3"}
        });

    My.Result.Show(affectedRows);
}

示例：执行Delete

单次

执行Delete语句一次

string sql = "DELETE FROM Invoice WHERE InvoiceID = @InvoiceID";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var affectedRows = connection.Execute(sql, new {InvoiceID = 1});

    My.Result.Show(affectedRows);
}

多次

执行多次，数组中的每条数据都执行一次

string sql = "DELETE FROM Invoice WHERE InvoiceID = @InvoiceID";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var affectedRows = connection.Execute(sql,
        new[]
        {
            new {InvoiceID = 1},
            new {InvoiceID = 2},
            new {InvoiceID = 3}
        });
}

Dapper Query查询

介绍

查询方法（Query）是IDbConnection的扩展方法，它可以用来执行查询（select）并映射结果到C#实体（Model、Entity）类

查询结果可以映射成如下类型：

Anonymous 匿名类型
Strongly Typed 强类型
Multi-Mapping (One to One) 多映射一对一
Multi-Mapping (One to Many) 多映射一对多
Multi-Type 多类型

参数

下面表格中显示了Query方法的不同参数

名称	描述
sql	要执行的sql语句文本
param	command的参数
transaction	事务
buffered	True to buffer readeing the results of the query (default = true). 翻译不来。。。
commandTimeout	command超时时间
commandType	command类型

示例 - 匿名查询

Raw SQL query can be executed using Query method and map the result to a dynamic list.

直接执行SQL语句字符串，然后将结果映射成 dynamic类型的List中

string sql = "SELECT * FROM Invoice;";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var invoices = connection.Query(sql).ToList();
    
    My.Result.Show(invoices);
}

示例 - 强类型查询（最常用）

直接执行SQL语句字符串，然后将结果映射成强类型类型的List中

string sql = "SELECT * FROM Invoice;";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var invoices = connection.Query<Invoice>(sql).ToList();
    
    My.Result.Show(invoices);
}

示例 - 多映射查询 (One to One)

Raw SQL query can be executed using Query method and map the result to a strongly typed list with a one to one relation.（没太理解）

直接执行SQL语句字符串，然后将结果用一对一的关系映射成强类型类型的List中

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();
        
    My.Result.Show(invoices);
}

示例 - 查询多映射 (One to Many)

Raw SQL query can be executed using Query method and map the result to a strongly typed list with a one to many relations.

直接执行SQL语句字符串，然后将结果用一对多的关系映射成强类型类型的List中

string sql = "SELECT * FROM Invoice AS A INNER JOIN InvoiceItem AS B ON A.InvoiceID = B.InvoiceID;";

using (var connection = My.ConnectionFactory())
{
    connection.Open();

    var invoiceDictionary = new Dictionary<int, Invoice>();

    var invoices = connection.Query<Invoice, InvoiceItem, Invoice>(
            sql,
            (invoice, invoiceItem) =>
            {
                Invoice invoiceEntry;
                
                if (!invoiceDictionary.TryGetValue(invoice.InvoiceID, out invoiceEntry))
                {
                    invoiceEntry = invoice;
                    invoiceEntry.Items = new List<InvoiceItem>();
                    invoiceDictionary.Add(invoiceEntry.InvoiceID, invoiceEntry);
                }

                invoiceEntry.Items.Add(invoiceItem);
                return invoiceEntry;
            },
            splitOn: "InvoiceID")
        .Distinct()
        .ToList();
        
    My.Result.Show(invoices);
}

示例 - Query Multi-Type

Raw SQL query can be executed using Query method and map the result to a list of different types.

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);
}

参考文章：

dapper toturial http://dapper-tutorial.net/dapper

http://dapper-tutorial.net/query

Dapper实用教程