如何为现有的AzureCosmosDB生成模型类？

Question

我有一个现有的Azure CosmosDB，里面有所有的数据和集合。现在，我希望基于我对SQLServer数据库所做的相同过程来生成模型类。

https://www.learnentityframeworkcore.com/walkthroughs/existing-database

我尝试了以下命令，使用cmd实用程序导航到包含解决方案文件的文件夹：

dotnet ef dbcontext scaffold <Azure CosmosDB ConnectionString> Microsoft.EntityFrameworkCore.Cosmos -o Models

在执行上面的命令时，我得到以下错误：

System.InvalidOperationException: Unable to find expected assembly attribute named DesignTimeProviderServicesAttribute in provider assembly Microsoft.EntityFrameworkCore.Cosmos. This attribute is required to identify the class which acts as the design-time service provider factory.
   at Microsoft.EntityFrameworkCore.Design.Internal.DesignTimeServicesBuilder.ConfigureProviderServices(String provider, IServiceCollection services, Boolean throwOnError)
   at Microsoft.EntityFrameworkCore.Design.Internal.DesignTimeServicesBuilder.Build(String provider)
   at Microsoft.EntityFrameworkCore.Design.Internal.DatabaseOperations.ScaffoldContext(String provider, String connectionString, String outputDir, String outputContextDir, String dbContextClassName, IEnumerable`1 schemas, IEnumerable`1 tables, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContextImpl(String provider, String connectionString, String outputDir, String outputDbContextDir, String dbContextClassName, IEnumerable`1 schemaFilters, IEnumerable`1 tableFilters, Boolean useDataAnnotations, Boolean overwriteFiles, Boolean useDatabaseNames)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.ScaffoldContext.<>c__DisplayClass0_1.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Unable to find expected assembly attribute named DesignTimeProviderServicesAttribute in provider assembly Microsoft.EntityFrameworkCore.Cosmos. This attribute is required to identify the class which acts as the design-time service provider factory.

有人能帮助我知道如何解决这个问题吗？

Answer 1

为了使其正常工作，数据库提供程序需要包含有关如何进行搭建的信息。目前，CosmosDB不支持此功能，因此您将无法使用命令行界面从现有数据库创建模型。

有一个Github issue open可以改进错误消息，使这一点更加清楚。如果你愿意，你可以在该repo上打开一个问题，请求为Cosmos添加该功能。