ORM 轻量级框架 Dapper（介绍）

Dapper是什么？

Dapper是.net 一个简单的对象映射，就速度而言，他是轻量数据 Orm 之王，他和Ado.net的DataReader一样快。ORM是对象关系映射器，负责数据库和编程语言之间的映射。

Dapper 继承了IDbConnection，通过扩展数据库查询方法进行数据库查询

Dapper可与任何数据库提供程序使用，没有特定的数据库实现。

Dapper怎样工作？

   主要分三个过程：

• 　　创建一个IDbConnection 对象
• 　　编写CRUD操作语句
• 　　将操作语句作为参数，传递给Execute 方法

安装

Dapper通过Negut进行安装:https://www.nuget.org/packages/Dapper

PM> Install-Package Dapper

方法

dapper使用多种方法扩展IDbConnection接口

• Execute
• Query
• QueryFirst
• QueryFirstOrDefault
• QuerySingle
• QuerySingleOrDefault
• QueryMultiple

string sqlOrderDetails = "SELECT TOP 5 * FROM OrderDetails;";
string sqlOrderDetail = "SELECT * FROM OrderDetails WHERE OrderDetailID = @OrderDetailID;";
string sqlCustomerInsert = "INSERT INTO Customers (CustomerName) Values (@CustomerName);";

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{
    var orderDetails = connection.Query<OrderDetail>(sqlOrderDetails).ToList();
    var orderDetail = connection.QueryFirstOrDefault<OrderDetail>(sqlOrderDetail, new {OrderDetailID = 1});
    var affectedRows = connection.Execute(sqlCustomerInsert,  new {CustomerName = "Mark"});

    Console.WriteLine(orderDetails.Count);
    Console.WriteLine(affectedRows);

    FiddleHelper.WriteTable(orderDetails);
    FiddleHelper.WriteTable(new List<OrderDetail>() { orderDetail });
}

　

参数

执行和查询可以使用多种不同类型的参数

• Anonymous
• Dynamic
• List
• String

// Anonymous
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,
    parameter,
    commandType: CommandType.StoredProcedure);

int rowCount = parameter.Get<int>("@RowCount");

// 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

查询方法返回的结果可以映射为不同类型

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

string sqlOrderDetails = "SELECT TOP 10 * FROM OrderDetails;";

using (var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServerW3Schools()))
{
    var anonymousList = connection.Query(sqlOrderDetails).ToList();
    var orderDetails = connection.Query<OrderDetail>(sqlOrderDetails).ToList();

    Console.WriteLine(anonymousList.Count);
    Console.WriteLine(orderDetails.Count);

    FiddleHelper.WriteTable(orderDetails);

    FiddleHelper.WriteTable(connection.Query(sqlOrderDetails).FirstOrDefault());
}

实用工具

• 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);