如何在多个实体数据模型之间共享连接字符串

Question

我有一个具有4个实体数据模型的项目，要构建它们，我不想在我的项目中保存连接字符串，而是要将连接字符串存储在app.config文件中并在我的模型之间共享，我该怎么做？

谢谢

Answer 1

假设首先是 DbContext 和模型/数据库。

1. 将生成的 EF 连接字符串保留在 app.config 文件中不变。正如 Arthur 所说，它们包含 EF 元数据 (csdl/ssdl/msl) 的路径。模型设计者也在开发过程中使用它们。
2. 添加一个名为“SharedConnection”的存储连接字符串。这是唯一需要在生产中修改的连接字符串。
3. 创建一个派生自 DbContext 的基类，并从该类派生所有上下文。
4. 在基类中显式创建默认 EF 连接。然后修改它以使用共享连接字符串，如下所示：

public class BaseContext : DbContext
{
    public BaseContext(string nameOrConnectionString)
        : base(CreateConnection(nameOrConnectionString), true)
    {
    }

    private static EntityConnection CreateConnection(string connectionString)
    {
        // Create a (plain old database) connection using the shared connection string.
        DbConnection dbConn = Database.DefaultConnectionFactory.CreateConnection(
            ConfigurationManager.ConnectionStrings["SharedConnection"].ConnectionString);

        // Create a helper EntityConnection object to build a MetadataWorkspace out of the
        // csdl/ssdl/msl parts of the generated EF connection string for this DbContext.
        EntityConnection wsBuilder = new EntityConnection(connectionString);

        // Merge the specific MetadataWorkspace and the shared DbConnection into a new EntityConnection.
        return new EntityConnection(wsBuilder.GetMetadataWorkspace(), dbConn);
    }
}

派生上下文的代码不会改变，只是它们必须继承自 BaseContext。这是一个更健壮的 CreateConnection 方法。它具有错误处理功能，并以添加应用程序设置为代价从代码中删除共享连接字符串的名称。

private static EntityConnection CreateConnection(string connectionString)
{
    // Find the name of the shared connection string.
    const string appSettingKey = "SharedConnectionStringName";

    string sharedConnectionStringName = ConfigurationManager.AppSettings[appSettingKey];
    if (string.IsNullOrEmpty(sharedConnectionStringName))
    {
        throw new Exception(string.Format(
            "Shared connection not configured. " +
            "Please add a setting called \"{0}\" to the \"appSettings\" " +
            "section of the configuration file.", appSettingKey));
    }

    // Create a (plain old database) connection using the shared connection string.
    ConnectionStringSettings backendSettings =
        ConfigurationManager.ConnectionStrings[sharedConnectionStringName];
    if (backendSettings == null)
    {
        throw new Exception(string.Format(
            "Invalid connection string name \"{0}\" in appSetting \"{1}\"",
            sharedConnectionStringName, appSettingKey));
    }

    System.Data.Common.DbConnection dbConn =
        Database.DefaultConnectionFactory.CreateConnection(
        backendSettings.ConnectionString);

    // Create a helper EntityConnection object to build a MetadataWorkspace out of the
    // csdl/ssdl/msl parts of the generated EF connection string for this DbContext.
    EntityConnection wsBuilder = new EntityConnection(connectionString);

    // Merge the specific MetadataWorkspace and the shared DbConnection into a new EntityConnection.
    return new EntityConnection(wsBuilder.GetMetadataWorkspace(), dbConn);
}