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?
尝试使用Database SetInitializer，它属于using System.Data.Entity;
在Global.asax
protected void Application_Start()
{
Database.SetInitializer(new DropCreateDatabaseIfModelChanges<yourContext>());
}
这将在每次模型更改时创建新的数据库。但是您的数据库将是空的。为了用虚拟数据填充它，你可以使用播种。你可以实现为:
播种::
protected void Application_Start()
{
Database.SetInitializer(new AddressBookInitializer());
----rest code---
}
public class AddressBookInitializer : DropCreateDatabaseIfModelChanges<AddressBook>
{
protected override void Seed(AddressBook context)
{
context.yourmodel.Add(
{
});
base.Seed(context);
}
}
这很奇怪，但这里所有的答案对我来说都没用。
对于我来说，有效的初始化器
MigrateDatabaseToLatestVersion
以下是我的解决方案(我知道，它可以简单得多，但这就是我使用它的方式):
class MyDbMigrateToLatest : MigrateDatabaseToLatestVersion<MyDbContext, Configuration>
{
}
public class MyDbContext: DbContext
{
public MyDbContext() : base("DbName")
{
SetInitializer();
}
public MyDbContext(string connString) : base(connString)
{
SetInitializer();
}
private static void SetInitializer()
{
if (ConfigurationManager.AppSettings["RebuildDatabaseOnStart"] == "true")
Database.SetInitializer(new MyDbInitializerForTesting());
else
Database.SetInitializer(new MyDbMigrateToLatest());
}
}
public sealed class Configuration : DbMigrationsConfiguration<MyDbContext>
{
public Configuration()
{
AutomaticMigrationsEnabled = true;
}
protected override void Seed(MyDbContext context)
{
// Whatever
}
}
MyDbInitializerForTesting只是继承自DropCreateDatabaseAlways，所以在某些特定的情况下(测试)，整个数据库被重建。否则，它已迁移到最新版本。
我的来源:https://msdn.microsoft.com/en-us/data/jj591621.aspx#specific
我花了很多天来解决这个问题，分析了很多不同的帖子，尝试了很多选择，最终解决了这个问题。
这2个项目在我的解决方案使用EF代码第一次迁移:
控制台应用程序“DataModel”，主要用作程序集，其中包含我所有的代码第一个实体，DbContext, Mirgations和通用存储库。我在这个项目中包含了单独的空本地数据库文件(在DataModel/App_Data文件夹中)，以便能够从包管理器控制台生成迁移。
WebApi引用了DataModel项目，并使用了WebApi/App_Data文件夹中的本地数据库文件，该文件不包含在项目中
当请求WebApi时，我得到了这个错误…
我的环境:
Windows 8.1 x64
Visual Studio 2015 Professional with Update 1
我所有的项目都针对。net Framework 4.6.1
EntityFramework 6.1.3 from NuGet
在这里，我收集了所有你应该注意的事项和所有必须满足的条件/要求，以避免提到的例外:
You should use only one version of EntityFramework Nuget package for all projects in your solution.
Database, created by running sequentially all migration scripts should have the same structure/schema as you target database and correspond to entity model. Following 3 things must exactly correspond/reflect/match each other:
Your all migration script up to last
Current code first entity model state (DbContext, entities)
Target database
Target database (mdf file) should be updated/correspond up to last migration script. Verify that "__MigrationHistory" table in your target database contains records for all migration scripts that you have, it means that all migration scripts was successfully applied to that database. I recommend you to use Visual Studio for generation correct code first entities and context that corresponds to your database, Project -> Add New Item -> ADO.NET Entity Data Model -> Code First from database:
Of course, as an alternative, if you have no database you can write manually model (code first entities and context) and then generate initial migration and database.
Name of connection string e.g. MyConnectionString in config file of startup project (Web.config/App.config):
<configuration>
<connectionStrings>
<add name="MyConnectionString" connectionString="...">
</connectionStrings>
<configuration>
should be equal to parameter passed in constructor of your DbContext:
public partial class MyDbContext : DbContext
{
public MyDbContext()
: base("name=MyConnectionString"){}
...
Before using Package Manager Console, make sure that you are using correct database for update or generate migration and needed project is set as startup project of solution. For connect to database it will use connection string from that .config file, which in project, that is set as startup project.
And the main, which fixed my issue: It is weird, but in my WebApi/bin folder DataModel.exe was old, not refreshed since last build. Since migrations was embedded in my assembly DataModel.exe then my WebApi updated database using old mirgations. I was confused why after updating database in WebApi it not corresponds to latest migration script from DataModel. Following code automatically creates(if not exists) or updates to latest migration local database in my WebApi/App_Data folder.
public class WebApiApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
Database.SetInitializer(new MigrateDatabaseToLatestVersion<ODS_DbContext, Configuration>());
...
I tried clean and rebuild solution but it did not help, than I completely removed
bin and obj folders from WebApi, deleted database files from WebApi/App_Data, built, restarted WebApi, made request to it, it created correct database - lazy initialization (using lines above), which corresponds to latest migration and exception didn't appear more.
So, this may fix your problem:
remove manually bin, obj folders from your startup project (which generates/updates your database)
build your startup project or better clean and rebuild all you solution.
recreate database by starting project (will execute lines above) or use Package Manager Console "update-database" command.
manually check whether generated db and __MirgationHistory corresponds to latest migration script.
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
创建自定义上下文初始化项:
public class MyDbContextInitializer : MigrateDatabaseToLatestVersion<MyDbContext, Migrations.Configuration>
{
public override void InitializeDatabase(MyDbContext context)
{
bool exists = context.Database.Exists();
base.InitializeDatabase(context);
if (!exists)
{
MyDbSeed.Seed(context);
}
}
}
注意迁移。Configuration是Package Manager Console中由迁移命令行生成的类。您可能需要将迁移的内部修饰符更改为公共修饰符。配置类。
并从您的OmModelCreating注册它:
public partial class MyDbContext : DbContext
{
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
Database.SetInitializer<MyDbContext>(new MyDbContextInitializer());
//other code for creating model
}
}
