错误信息:

“自数据库创建以来,支持‘AddressBook’上下文的模型已经发生了变化。手动删除/更新数据库,或者调用database。带有IDatabaseInitializer实例的SetInitializer。例如,RecreateDatabaseIfModelChanges策略将自动删除并重新创建数据库,并可选地为其添加新数据。”

我正在尝试使用代码优先功能,以下是我写的:

var modelBuilder = new ModelBuilder();
var model = modelBuilder.CreateModel();
using (AddressBook context = new AddressBook(model))
{
    var contact = new Contact
    {
        ContactID = 10000,
        FirstName = "Brian",
        LastName = "Lara",
        ModifiedDate = DateTime.Now,
        AddDate = DateTime.Now,
        Title = "Mr."

    };
    context.contacts.Add(contact);
    int result = context.SaveChanges();
    Console.WriteLine("Result :- "+ result.ToString());
}

上下文类:

public class AddressBook : DbContext
{
    public AddressBook()
    { }
    public AddressBook(DbModel AddressBook)
        : base(AddressBook)
    {

    }
    public DbSet<Contact> contacts { get; set; }
    public DbSet<Address> Addresses { get; set; }
}

和连接字符串:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
    <add name="AddressBook" providerName="System.Data.SqlClient"  
         connectionString="Data Source=MyMachine;Initial Catalog=AddressBook;
         Integrated Security=True;MultipleActiveResultSets=True;"/>
    </connectionStrings>
</configuration>

因此,数据库名称是“AddressBook”,当我试图将联系人对象添加到上下文时发生错误。我遗漏了什么吗?


当前回答

好建议,但并非在所有情况下都如此准确。我算出一个。 请确保您在Visual Studio中使用PM窗口运行“enable-migrations”,迁移文件夹将添加到您的项目中。

确保添加到文件夹中的两个c#类文件将包含所有模型及其各自的属性。

如果您拥有所有这些,就构建解决方案,并发布部署。

逻辑是不能覆盖现有元数据,因为应用程序没有元数据来替换当前元数据。结果,你会得到这样的错误“支持上下文的模型自数据库创建以来已经改变了”

其他回答

在这里,我想分享另一种防止上下文改变时模型备份错误的方法:

1)打开DbContext文件

2)使用Microsoft.AspNet.Identity.EntityFramework添加命名空间;

3) public MyDbContext() : base(“name=MyDbContext”) { Database.SetInitializer(new DropCreateDatabaseAlways()); }

刚刚找到答案,想在这里更新。只需要做以下事情。

public class AddressBook: DbContext
{
   protected override void OnModelCreating(ModelBuilder modelBuilder)
   {
    modelBuilder.IncludeMetadataInDatabase = false;
   }
}

当我们为两个应用程序使用一个数据库时,我遇到了同样的问题。设置disableDatabaseInitialization="true"在上下文类型节为我工作。

<entityFramework>
<providers>
  <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
</providers>
<contexts>
  <context type="PreferencesContext, Preferences" disableDatabaseInitialization="true">
    <databaseInitializer type="System.Data.Entity.MigrateDatabaseToLatestVersion`2[[PreferencesContext, Preferences], [Migrations.Configuration, Preferences]], EntityFramework" />
  </context>
</contexts>

详情https://msdn.microsoft.com/en-us/data/jj556606.aspx

以下是Jeff在Scott Gu的博客上发布的一些信息:

For those who are seeing this exception: "The model backing the 'Production' context has changed since the database was created. Either manually delete/update the database, or call Database.SetInitializer with an IDatabaseInitializer instance." Here is what is going on and what to do about it: When a model is first created, we run a DatabaseInitializer to do things like create the database if it's not there or add seed data. The default DatabaseInitializer tries to compare the database schema needed to use the model with a hash of the schema stored in an EdmMetadata table that is created with a database (when Code First is the one creating the database). Existing databases won’t have the EdmMetadata table and so won’t have the hash…and the implementation today will throw if that table is missing. We'll work on changing this behavior before we ship the fial version since it is the default. Until then, existing databases do not generally need any database initializer so it can be turned off for your context type by calling: Database.SetInitializer<YourDbContext>(null); Jeff

I am reading the Pro ASP.NET MVC 4 book as well, and ran into the same problem you were having. For me, I started having the problem after making the changes prescribed in the 'Adding Model Validation' section of the book. The way I resolved the problem is by moving my database from the localdb to the full-blown SQL Server 2012 server. (BTW, I know that I am lucky I could switch to the full-blown version, so don't hate me. ;-))) There must be something with the communication to the db that is causing the problem.