HOW TO：实体框架的动态连接字符串

Question

喜欢标题。我该怎么做？

我尝试了一些东西，但是没有按我预期的那样工作。

我正在使用实体框架模型。我需要像参数一样传递连接字符串，因此，在另一个文件中，我编写了

namespace MyNamespace.Model
{
    using System;
    using System.Data.Entity;
    using System.Data.Entity.Infrastructure;

    public partial class MyEntities: DbContext
    {
        public MyEntities(string nameOrConnectionString) : base(nameOrConnectionString)
        {

        }
    }
}

启动应用程序时，我会以这种方式调用此构造函数，因此无论如何我都可以在应用程序中引用它：

public static MyEntities dbContext = new MyEntities(mdlImpostazioni.SetConnectionString());

其中mdlImpostazioni.SetConnectionString（）返回一个字符串（数据正确）：

server=192.168.1.100\SVILUPPO;database=MyDB;uid=myName;pwd=111111;

当我执行此代码时，似乎一切正常，但是当我尝试进行如下查询时：

var query = (from r in MainWindow.dbContext.TabTipoSistema select r);

它从这里抛出异常：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    throw new UnintentionalCodeFirstException(); //exception here
}

所以，这是一种糟糕的方法...正确的方法是？（仅使用代码C＃，不使用xaml）

Answer 1

您的方法是正确的，但是您需要记住EF的连接字符串需要元数据等。因此，请使用EntityConnectionStringBuilder。例如：

// the model name in the app.config connection string (any model name - Model1?)
private static string GetConnectionString(string model, YourSettings settings)
{
    // Build the provider connection string with configurable settings
    var providerSB = new SqlConnectionStringBuilder
    {
        // You can also pass the sql connection string as a parameter instead of settings
        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();

}
// Or just pass the connection string
private static string GetConnectionString(string model, string providerConnectionString)
{

    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 = providerConnectionString;
    // 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);
    // Make sure the "res://*/..." matches what's already in your config file.
    return efConnection.ToString();

}

编辑

您得到的异常是因为当您传递纯SQL连接字符串时，它假定您首先使用Code，因此它将调用OnModelCreation事件。如上所示，当您包括MetaData部分时，将告诉EF这是一个完整的EF连接字符串。