使用策略設計模式逐步指南在 C# 中實作資料庫助手-mysql教程-PHP中文網

Implementing a Database Helper in C# Using the Strategy Design Pattern Step-by-Step Guide

第 1 步：定義策略介面

首先建立一個介面 ISQLStrategy，聲明 GetDataTable 方法，該方法將由不同的資料庫策略實作。

using System.Data;

namespace MyProject.Util
{
    public interface ISQLStrategy
    {
        DataTable GetDataTable(string sql);
    }
}

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第 2 步：實施具體策略

接下來，為每個資料庫類型（MySQL、PostgreSQL 和 SQL Server）實作 ISQLStrategy 介面。

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;
            }
        }
    }
}

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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;
            }
        }
    }
}

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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;
            }
        }
    }
}

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第 3 步：建立上下文類別

SQLStrategy 類別將使用 ISQLStrategy 的執行個體來執行資料庫操作。

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);
        }
    }
}

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第 4 步：實作客戶端程式碼

最後，寫客戶端程式碼來測試策略模式的實作。

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();
            }
        }
    }
}

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總結

定義策略介面：使用 GetDataTable 方法建立介面 ISQLStrategy。
實作具體策略：實作 MySQL、PostgreSQL 和 SQL Server 的介面。
建立Context類別：使用SQLStrategy類別與策略互動。
編寫客戶端程式碼：透過查詢資料庫來測試實作。
這種方法可以讓您輕鬆地在不同的資料庫實作之間切換！

完整編碼

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();
            }
        }
    }
}

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