我对Entity Framework甚至ADO.NET都是全新的(通常不会对数据库做太多工作) .
-
我下载并安装了MySQL Connector/NET 6.3.5 .
-
我在Visual Studio 2010中创建了一个新的C#项目 .
-
我在我的项目中添加了一个新的ADO.NET实体数据模型并选择了"Generate from database."
-
我添加了一个新的连接到我的本地MySQL服务器w /服务器名称"localhost"我的用户名和密码 .
-
我检查了MySQL数据库中的所有表以生成对象 .
-
我写了以下代码:
( things
只是一个虚假的表格,我和一些任意字段一起扔了 . )
TestDataEntities entities = new TestDataEntities();
var things = entities.things.Execute(MergeOption.AppendOnly); // exception
上面扔了一个 NullReferenceException
,我甚至知道还有什么可以调查 .
对于那些真正了解这些东西的人来说,这是我得到的例外(但是,对于我未经训练的眼睛,这实际上看起来并没有那么有用):
at MySql.Data.MySqlClient.MySqlClientFactory.get_MySqlDbProviderServicesInstance()
at MySql.Data.MySqlClient.MySqlClientFactory.System.IServiceProvider.GetService(Type serviceType)
at System.Data.Common.DbProviderServices.GetProviderServices(DbProviderFactory factory)
at System.Data.Metadata.Edm.StoreItemCollection.Loader.InitializeProviderManifest(Action`3 addError)
at System.Data.Metadata.Edm.StoreItemCollection.Loader.OnProviderManifestTokenNotification(String token, Action`3 addError)
at System.Data.EntityModel.SchemaObjectModel.Schema.HandleProviderManifestTokenAttribute(XmlReader reader)
at System.Data.EntityModel.SchemaObjectModel.Schema.HandleAttribute(XmlReader reader)
at System.Data.EntityModel.SchemaObjectModel.SchemaElement.ParseAttribute(XmlReader reader)
at System.Data.EntityModel.SchemaObjectModel.SchemaElement.Parse(XmlReader reader)
at System.Data.EntityModel.SchemaObjectModel.Schema.HandleTopLevelSchemaElement(XmlReader reader)
at System.Data.EntityModel.SchemaObjectModel.Schema.InternalParse(XmlReader sourceReader, String sourceLocation)
at System.Data.EntityModel.SchemaObjectModel.Schema.Parse(XmlReader sourceReader, String sourceLocation)
at System.Data.EntityModel.SchemaObjectModel.SchemaManager.ParseAndValidate(IEnumerable`1 xmlReaders, IEnumerable`1 sourceFilePaths, SchemaDataModelOption dataModel, AttributeValueNotification providerNotification, AttributeValueNotification providerManifestTokenNotification, ProviderManifestNeeded providerManifestNeeded, IList`1& schemaCollection)
at System.Data.Metadata.Edm.StoreItemCollection.Loader.LoadItems(IEnumerable`1 xmlReaders, IEnumerable`1 sourceFilePaths)
at System.Data.Metadata.Edm.StoreItemCollection.Init(IEnumerable`1 xmlReaders, IEnumerable`1 filePaths, Boolean throwOnError, DbProviderManifest& providerManifest, DbProviderFactory& providerFactory, Memoizer`2& cachedCTypeFunction)
at System.Data.Metadata.Edm.StoreItemCollection..ctor(IEnumerable`1 xmlReaders, IEnumerable`1 filePaths)
at System.Data.Metadata.Edm.MetadataCache.StoreMetadataEntry.LoadStoreCollection(EdmItemCollection edmItemCollection, MetadataArtifactLoader loader)
at System.Data.Metadata.Edm.MetadataCache.StoreItemCollectionLoader.LoadItemCollection(StoreMetadataEntry entry)
at System.Data.Metadata.Edm.MetadataCache.LoadItemCollection[T](IItemCollectionLoader`1 itemCollectionLoader, T entry)
at System.Data.Metadata.Edm.MetadataCache.GetOrCreateStoreAndMappingItemCollections(String cacheKey, MetadataArtifactLoader loader, EdmItemCollection edmItemCollection, Object& entryToken)
at System.Data.EntityClient.EntityConnection.LoadStoreItemCollections(MetadataWorkspace workspace, DbConnection storeConnection, DbProviderFactory factory, DbConnectionOptions connectionOptions, EdmItemCollection edmItemCollection, MetadataArtifactLoader artifactLoader)
at System.Data.EntityClient.EntityConnection.GetMetadataWorkspace(Boolean initializeAllCollections)
at System.Data.EntityClient.EntityConnection.InitializeMetadata(DbConnection newConnection, DbConnection originalConnection, Boolean closeOriginalConnectionOnFailure)
at System.Data.EntityClient.EntityConnection.Open()
at System.Data.Objects.ObjectContext.EnsureConnection()
at System.Data.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption)
at System.Data.Objects.ObjectQuery`1.Execute(MergeOption mergeOption)
at EntityFrameworkTest.Form1..ctor() in D:\Development\EntityFrameworkTest\Form1.cs:line 23
at EntityFrameworkTest.Program.Main() in D:\Development\EntityFrameworkTest\Program.cs:line 18
at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
5 回答
我通过添加对MySql.Data.Entity.dll(和MySql.Web.dll)的引用来解决此错误
这是一个提供程序错误 . 它可能是由配置错误触发的错误,但它仍然是提供程序错误 . 您应该与编写MySQL提供程序的人员交谈,并向他们发送堆栈和测试用例 .
好消息 !此问题已在MySQL Connector/NET 6.3.6中解决 . 更新MySql连接器以解决问题 .
好吧,我不应该这样做(如果是的话,我有点尴尬 - 尽管在我的辩护中,我没有看到任何明确指出的地方);但它似乎 the problem was that I had my target framework set to .NET 3.5 . 在将项目的目标框架(老实说,一时兴起)更改为.NET 4.0之后,
NullReferenceException
消失了 .因此,尽管不尽如人意,但这似乎是我案例中的解决方案 .
在MySqlClientFactory-> MySqlDbProviderServicesInstance属性中 . 它引用了ass:MySql.Data.Entity使用代码
string str = Assembly.GetExecutingAssembly().FullName.Replace("MySql.Data", "MySql.Data.Entity");
但是在MySql Client 6.3.5中,MySqlData的版本是6.3.5,而MySql.Data.Entity的版本是6.3.4(在\ Program Files \ MySQL \ MySQL Connector Net 6.3.5 \ Assemblies \ v2.0中).so它无法成功加载 .
在文件夹(\ Program Files \ MySQL \ MySQL Connector Net 6.3.5 \ Assemblies \ v4.0)中,MySql.Data.Entity的版本为6.3.5,因此可以加载成功 .
因此,一种方法是将目标更改为.NET 4.0,另一种方法是将MySql.Data转回6.3.2 / 6.1.2 .