c# - 如何将 Entity Framework (代码优先)与动态创建的连接字符串和单文件数据库一起使用？

Question

我正在使用代码优先的 SqlServerCompact Entity Framework ，并且动态生成连接字符串，因为它是在用户请求时生成的数据库。

我遵循了这个问题的建议:How do I programmatically set the connection string for Entity-Framework Code-First?但是，我仍然有问题，事实上我得到一个异常，提示模型中的架构与代码中使用的架构不同。

然而，这很明显，我希望从代码生成模式，所以我真的不明白为什么会这样

有人可以帮我吗？这是使用的代码:

NerdDinners.cs

class NerdDinners : DbContext
{
    public static string CreateConnectionString(string dbPath = @"|DataDirectory|\NerdDinners.sdf")
    {
        SqlCeConnectionStringBuilder sqlConnection = new SqlCeConnectionStringBuilder();
        sqlConnection.Password = "9023fase93";
        sqlConnection.DataSource = dbPath;

        EntityConnectionStringBuilder connection = new EntityConnectionStringBuilder();
        connection.Metadata = @"res://*/NerdDinnersModel.csdl|res://*/NerdDinnersModel.ssdl|res://*/NerdDinnersModel.msl";
        connection.Provider = "System.Data.SqlServerCe.3.5";
        connection.ProviderConnectionString = sqlConnection.ToString();

        return connection.ToString();
    }

    public NerdDinners() : base() { }
    public NerdDinners(string nameOrConnectionString) : base(nameOrConnectionString) { }

    public DbSet<Dinner> Dinners { get; set; }
    public DbSet<RSVP> RSVPs { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        Database.SetInitializer<NerdDinners>(new NerdDinnersInitializer());
        Database.DefaultConnectionFactory = new SqlCeConnectionFactory("System.Data.SqlServerCe");

        base.OnModelCreating(modelBuilder);
    }
}

Program.cs

class Program
{
    static void Main(string[] args)
    {
        NerdDinners nerdDinner = new NerdDinners(NerdDinners.CreateConnectionString());
        Console.WriteLine("Inizio test");

        var res = from d in nerdDinner.Dinners
                  select d;

        Console.WriteLine("Dinners:");
        foreach (var item in res)
            Console.WriteLine(item.ToString());
        Console.WriteLine("End");

        // Usato per terminazione
        Console.ReadKey();
    }
}

这是我的解决方案(图片):

编辑 1:

错误是一个 MetadataException，它提示无效的模式

编辑 2:

NerdDinnersInitializer.cs

class NerdDinnersInitializer : DropCreateDatabaseAlways<NerdDinners>
{
    public NerdDinnersInitializer() : base() { }

    protected override void Seed(NerdDinners context)
    {
        var toadd = new List<Dinner>
        {
            new Dinner
            {
                Address = "bla",
                DinnerID = 0,
                EventDate = DateTime.Parse("2010-12-03"),
                HostedBy = "mclink",
                Title = "Notitle",
            },
            new Dinner
            {
                Address = "Fiwe",
                DinnerID = 0,
                EventDate = DateTime.Parse("2011-12-03"),
                HostedBy = "ngi",
                Title = "Bah",
            },
        };

        toadd.ForEach(item => context.Dinners.Add(item));

        context.SaveChanges();

        base.Seed(context);
    }
}

Answer 1

我不确定这是否适用于您的情况，但如果模型与当前现有的数据库架构不匹配，您可能会收到错误消息。你需要做类似的事情-

Database.SetInitializer<NerdDinners>(
    new DropCreateDatabaseIfModelChanges<NerdDinners>());

这将删除现有数据库并根据您的模型创建一个新数据库。

您的示例代码中确实有一些代码可以设置初始值设定项 -

Database.SetInitializer<NerdDinners>(new NerdDinnersInitializer());

但我不确定您的 NerdDinnersInitializer 类在做什么。