第 1 步：定义策略接口
首先创建一个接口isqlstrategy，声明getdatatable方法，该方法将由不同的数据库策略实现。
using system.data;
namespace myproject.util
{
public interface isqlstrategy
{
datatable getdatatable(string sql);
}
}
第 2 步：实施具体策略
接下来，为每种数据库类型（mysql、postgresql 和 sql server）实现 isqlstrategy 接口。
mysql 策略：
using mysql.data.mysqlclient;
using system;
using system.configuration;
using system.data;
namespace myproject.util
{
public class mysqlquery : isqlstrategy
{
public datatable getdatatable(string sql)
{
try
{
using (mysqlconnection conn = new mysqlconnection(configurationmanager.appsettings["mysqlconnectionstring"]))
{
datatable dt = new datatable();
conn.open();
mysqlcommand command = new mysqlcommand(sql, conn);
dt.load(command.executereader());
conn.close();
return dt;
}
}
catch (exception e)
{
console.writeline(e.tostring());
return null;
}
}
}
}
postgresql 策略：
using npgsql;
using system;
using system.configuration;
using system.data;
namespace myproject.util
{
public class npgsqlquery : isqlstrategy
{
public datatable getdatatable(string sql)
{
try
{
using (npgsqlconnection conn = new npgsqlconnection(configurationmanager.appsettings["npgsqlconnectionstring"]))
{
datatable dt = new datatable();
conn.open();
npgsqlcommand command = new npgsqlcommand(sql, conn);
npgsqldataadapter _dap = new npgsqldataadapter(command);
_dap.fill(dt);
conn.close();
return dt;
}
}
catch (exception e)
{
console.writeline(e.tostring());
return null;
}
}
}
}
sql server 策略：
using system;
using system.configuration;
using system.data;
using system.data.sqlclient;
namespace myproject.util
{
public class tsqlquery : isqlstrategy
{
public datatable getdatatable(string sql)
{
try
{
using (sqlconnection conn = new sqlconnection(configurationmanager.appsettings["tsqlconnectionstring"]))
{
datatable dt = new datatable();
conn.open();
sqlcommand command = new sqlcommand(sql, conn);
sqldataadapter da = new sqldataadapter(command);
da.fill(dt);
conn.close();
return dt;
}
}
catch (exception e)
{
console.writeline(e.tostring());
return null;
}
}
}
}
第 3 步：创建上下文类
sqlstrategy 类将使用 isqlstrategy 的实例来执行数据库操作。
using system.data;
namespace myproject.util
{
public class sqlstrategy
{
private readonly isqlstrategy _sqlstrategy;
public sqlstrategy(isqlstrategy sqlstrategy)
{
_sqlstrategy = sqlstrategy;
}
public datatable getdatatable(string sql)
{
return _sqlstrategy.getdatatable(sql);
}
}
}
第 4 步：实施客户端代码
最后，编写客户端代码来测试策略模式的实现。
using system;
using system.data;
namespace myproject.util
{
public class client
{
public static void main()
{
sqlstrategy sqlhelper = new(new tsqlquery());
datatable result = sqlhelper.getdatatable("select top (10) * from [product]");
foreach (datarow row in result.rows)
{
foreach (datacolumn column in result.columns)
{
console.write($"{column.columnname}: {row[column]} \t");
}
console.writeline();
}
}
}
}
总结
- 定义策略接口：使用 getdatatable 方法创建接口 isqlstrategy。
- 实施具体策略：实现 mysql、postgresql 和 sql server 的接口。
- 创建context类：使用sqlstrategy类与策略交互。
- 编写客户端代码：通过查询数据库来测试实现。
- 这种方法可以让您轻松地在不同的数据库实现之间切换！
完整编码
using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using Npgsql;
using MySql.Data.MySqlClient;
namespace MyProject.Util
{
//Strategy (Interface)
public interface ISQLStrategy
{
DataTable GetDataTable(string sql);
//You could add more methods for "Create", "Update" as well
}
//Concrete Strategies
public class MySQLQuery : ISQLStrategy
{
public DataTable GetDataTable(string sql)
{
try
{
using (MySqlConnection conn = new MySqlConnection(ConfigurationManager.AppSettings["MySqlConnectionString"]))
{
DataTable dt = new DataTable();
conn.Open();
MySqlCommand command = new MySqlCommand(sql, conn);
dt.Load(command.ExecuteReader());
conn.Close();
return dt;
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
return null;
}
}
}
public class NpgSqlQuery : ISQLStrategy
{
public DataTable GetDataTable(string sql)
{
try
{
using (NpgsqlConnection conn = new NpgsqlConnection(ConfigurationManager.AppSettings["NpgSqlConnectionString"]))
{
DataTable dt = new DataTable();
conn.Open();
NpgsqlCommand command = new NpgsqlCommand(sql, conn);
NpgsqlDataAdapter _dap = new NpgsqlDataAdapter(command);
_dap.Fill(dt);
conn.Close();
return dt;
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
return null;
}
}
}
public class TSqlQuery : ISQLStrategy
{
public DataTable GetDataTable(string sql)
{
try
{
using (SqlConnection conn = new SqlConnection(ConfigurationManager.AppSettings["TSqlConnectionString"]))
{
DataTable dt = new DataTable();
conn.Open();
SqlCommand command = new SqlCommand(sql, conn);
SqlDataAdapter da = new SqlDataAdapter(command);
da.Fill(dt);
conn.Close();
return dt;
}
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
return null;
}
}
}
//Context
public class SQLStrategy
{
public ISQLStrategy _sqlStrategy;
public SQLStrategy(ISQLStrategy sqlStrategy)
{
_sqlStrategy = sqlStrategy;
}
public DataTable GetDataTable(string sql)
{
return _sqlStrategy.GetDataTable(sql);
}
}
// Testing the Strategy Design Pattern
// Client Code
public class Client
{
public static void Main()
{
SQLStrategy sqlHelper = new(new TSqlQuery());
DataTable result = sqlHelper.GetDataTable("SELECT TOP (10) * FROM [Product]");
foreach (DataRow row in result.Rows)
{
foreach (DataColumn column in result.Columns)
{
Console.Write($"{column.ColumnName}: {row[column]} \t");
}
Console.WriteLine();
}
}
}
}
热爱 c#！
