Castle ActiveRecord 組態封裝方案：工廠模式實現多資料庫通用初始化

痛點：重複的組態字串難維護

每個專案都要在 web.config 或程式碼中重複寫入 hibernate.connection.driver_class、dialect、connection_string 等鍵值，易出錯且難以切換資料庫。

解決方案：工廠模式封裝初始化邏輯

1. 定義抽象初始化介面

public abstract class ActiveRecordInitializer
{
    public abstract void Initialize(string databaseName, string modelAssembly);
}

2. 實作不同資料庫的具體初始化類別

public class SqlServerInitializer : ActiveRecordInitializer
{
    public override void Initialize(string databaseName, string modelAssembly)
    {
        var properties = new Hashtable
        {
            ["hibernate.connection.driver_class"] = "NHibernate.Driver.SqlClientDriver",
            ["hibernate.dialect"] = "NHibernate.Dialect.MsSql2000Dialect",
            ["hibernate.connection.provider"] = "NHibernate.Connection.DriverConnectionProvider",
            ["hibernate.connection.connection_string"] =
                $"Data Source=.;Initial Catalog={databaseName};Integrated Security=SSPI"
        };
        var source = new InPlaceConfigurationSource();
        source.Add(typeof(ActiveRecordBase), properties);
        ActiveRecordStarter.Initialize(Assembly.Load(modelAssembly), source);
        ActiveRecordStarter.CreateSchema();
    }
}

public class MySqlInitializer : ActiveRecordInitializer
{
    public override void Initialize(string databaseName, string modelAssembly)
    {
        var properties = new Hashtable
        {
            ["hibernate.connection.driver_class"] = "NHibernate.Driver.MySqlDataDriver",
            ["hibernate.dialect"] = "NHibernate.Dialect.MySQLDialect",
            ["hibernate.connection.provider"] = "NHibernate.Connection.DriverConnectionProvider",
            ["hibernate.connection.connection_string"] =
                $"Server=localhost;Database={databaseName};Uid=root;Pwd=123;CharSet=utf8;"
        };
        var source = new InPlaceConfigurationSource();
        source.Add(typeof(ActiveRecordBase), properties);
        ActiveRecordStarter.Initialize(Assembly.Load(modelAssembly), source);
        ActiveRecordStarter.CreateSchema();
    }
}

3. 工廠類別：根據型別回傳對應初始化器

public static class ActiveRecordFactory
{
    public static ActiveRecordInitializer Create(string dbType)
    {
        return dbType.ToUpper() switch
        {
            "SQL" => new SqlServerInitializer(),
            "MYSQL" => new MySqlInitializer(),
            _ => new SqlServerInitializer()
        };
    }
}

4. 使用方式：一行程式碼完成初始化

// 在 Global.asax Application_Start 中
var initializer = ActiveRecordFactory.Create("SQL"); // 或 "MYSQL"
initializer.Initialize("MyDatabase", "MyProject.Model");

進階擴充建議

• 將連線字串參數化（Server、UID、PWD 從 appSettings 讀取）。
• 支援 PostgreSQL、Oracle、SQLite 只需新增對應 Initializer。
• 生產環境移除 CreateSchema()，改用 FluentMigrator 或 Flyway 管理版本。
• 搭配 Dependency Injection 容器（如 Windsor）註冊 ActiveRecordInitializer 介面，實現完全解耦。

總結

透過**工廠模式 + 策略模式**封裝 ActiveRecord 初始化邏輯，達到：

1. 零重複組態：連線參數集中管理。
2. 多資料庫熱插拔：新增資料庫只需加類別、改工廠。
3. 測試友善：單元測試可注入 In-Memory SQLite 初始化器。