entity-framework-4 - EF 4 代码优先 : Model compatibility cannot be checked because the EdmMetadata type was not included in the model

Question

我正在尝试使用 EF 4 Code First 模式。我的初始化代码如下:

创建模型生成器:

private static DbModelBuilder CreateModelBuild()
{
    var builder = new DbModelBuilder();

    //add entity classes about 12 of them

    builder.Conventions.Remove<IncludeMetadataConvention>();
    return builder;
}

创建 session :

private bool BuildSqlServerSession(DbModelBuilder builder)
{
    var model =
    builder.Build(new SqlConnection(@"connection string"));
    var cm = model.Compile();
    var context = new LittlePOSContext(cm);
    var dbExists = context.Database.Exists();
    _session = new EFSession(context);
    return dbExists;
}

这在我第一次运行代码时有效。但是当第二次运行并尝试使用 context.Add(myEntity) 添加对象时我得到以下异常:

Model compatibility cannot be checked because the EdmMetadata type was not 
included in the model. Ensure that IncludeMetadataConvention has been added 
to the DbModelBuilder conventions.

我尝试删除以下行:

builder.Conventions.Remove<IncludeMetadataConvention>();

但我仍然收到错误。

Answer 1

嗯，感觉有点傻，但真正的罪魁祸首是以下声明:

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

看来 DropCreateDatabaseIfModelChanges与 Code First 不兼容方法或者是其他一些我不明白的谜(还)。