使用策略设计模式分步指南在 C# 中实现数据库助手

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]} 	");
                }
                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]} 	");
                }

                Console.WriteLine();
            }
        }
    }
}

热爱 c#！

以上就是使用策略设计模式分步指南在 C# 中实现数据库助手的详细内容，更多请关注其它相关文章！