Question

有人可以帮我理解以下两种将连接字符串传递给DbContext的方法吗？

方法＃1：

public EWebDBContextEMS() : base("mainConnectionString")
{
}

和方法＃2：

public EWebDBContextEMS() : base("name=mainConnectionString")
{
}

This article states name=...将由设计师创建，但我使用纯DbContext代码进行测试，它也能正常运行。

这是DbContext构造函数的意图吗？在documentation中，没有提到连接字符串可以接受name=。

非常感谢

Answer 1

类DBContext类备注有完整的解释简而言之：

您的第一个示例可能会导致名为＆＃34; mainConnectionString＆＃34;被创造。
name = xxxx在app.config中查找名称为

某些工具确实为您添加了App.config中的条目您链接的在线文档准确说明了帮助的位置。

在线帮助说：

使用给定的字符串作为名称构造一个新的上下文实例或连接将要连接到的数据库的连接字符串制作。请参阅类备注，了解如何使用它来创建连接。

如果你去上课评论，你会找到一个完整的解释......

///               The connection to the database (including the name of the database) can be specified in several ways.
///             If the parameterless DbContext constructor is called from a derived context, then the name of the derived context
///             is used to find a connection string in the app.config or web.config file.  If no connection string is found, then
///             the name is passed to the DefaultConnectionFactory registered on the <see cref="T:System.Data.Entity.Database"/> class.  The connection
///             factory then uses the context name as the database name in a default connection string.  (This default connection
///             string points to .\SQLEXPRESS on the local machine unless a different DefaultConnectionFactory is registered.)
///             Instead of using the derived context name, the connection/database name can also be specified explicitly by
///             passing the name to one of the DbContext constructors that takes a string.  The name can also be passed in
///             the form "name=myname", in which case the name must be found in the config file or an exception will be thrown.
///             Note that the connection found in the app.config or web.config file can be a normal database connection
///             string (not a special Entity Framework connection string) in which case the DbContext will use Code First.
 ///             However, if the connection found in the config file is a special Entity Framework connection string, then the
 ///             DbContext will use Database/Model First and the model specified in the connection string will be used.
 ///             An existing or explicitly created DbConnection can also be used instead of the database/connection name.
 ///             A <see cref="T:System.Data.Entity.DbModelBuilderVersionAttribute"/> can be applied to a class derived from DbContext to set the
 ///             version of conventions used by the context when it creates a model. If no attribute is applied then the
 ///             latest version of conventions will be used.

Answer 2

第一种方法允许您在运行时创建自己的完整连接字符串，而不是app.config或web.config文件中的命名连接字符串。

方法2在配置文件中使用命名连接字符串。

使用方法1和处理连接字符串构建的部分类，您可以在运行时构建连接字符串，如：

DbContext构造函数接受连接字符串作为参数。你可能最好建立一个连接字符串并将其传递给构造函数，如下所示：

我使用了类似的东西：

// the model name in the app.config connection string (any model name - Model1?)
private static string GetConnectionString(string model, settings)
{
    // Build the provider connection string with configurable settings
    var providerSB = new SqlConnectionStringBuilder
    {
        InitialCatalog = settings.InitialCatalog,
        DataSource = settings.DataSource,
        UserID = settings.User,
        Password = settings.Password
    };

    var efConnection = new EntityConnectionStringBuilder();
    // or the config file based connection without provider connection string
    // var efConnection = new EntityConnectionStringBuilder(@"metadata=res://*/model1.csdl|res://*/model1.ssdl|res://*/model1.msl;provider=System.Data.SqlClient;");
    efConnection.Provider = "System.Data.SqlClient";
    efConnection.ProviderConnectionString = providerSB.ConnectionString;
    // based on whether you choose to supply the app.config connection string to the constructor
    efConnection.Metadata = string.Format("res://*/Model.{0}.csdl|res://*/Model.{0}.ssdl|res://*/Model.{0}.msl", model); ;
    return efConnection.ToString();

}

具有连接字符串的Entity Framework DbContext构造函数

2 个答案: