Code templates for scaffolding entity types and DbContext from an existing database

[rowanmiller]

We have one seam at the moment where folks can get a hold of the IModel we build from the database and manipulate it. We haven't really done any usability testing on this to see if it is good for changing table name conventions, etc..

We will also want some higher level extensibility points, such as code generation templates.

[abelepereira]

Where is this IModel manipulation being allowed? I guess some sort of extension over the default ef command (EntityFramework.Commands) need to be implemented, but where? Also: does this "extension" for model customization implies creating a new command assembly or will the default EntityFramework.Commands allow some sort of DI?

Regards

[rowanmiller]

The seam we have at the moment is designed for providers to use... so yes, you probably need to implement at least some parts of the provider to use it. This issue is about creating some high level seams that can be used by the application developer.

[dazinator]

Just wanted to check my understanding - as of the present release there is no way for an application developer to customise the code generated via scaffolding (a provider writer can), although in earlier releases there was a razor based template approach which has since been pulled? So essentially to do stuff like pluralisation etc we are waiting for the resolution of this issue - is that correct?

[rowanmiller]

@dazinator yes, that is correct. Post the 7.0.0 release we plan to provide customizable code-gen templates and code based interception points where you can customize the reverse engineered model and how it is written out to code.

[idg10]

One problem with this approach is that the existing model seems to support just one Name for an entity, which is used for both the generated type, and also for the property on the context. This means that if you want an entity type called Customer but and you want the DbSet<Customer> on your context to be called Customers, it doesn't look like you can do it, because the code gen pulls the name of both the type and that property from the IEntitySet.Name property.

I've worked through an attempt to singularize some names. (I'm working with a database where all the tables have plural names. Leaving this as is produces correct-sounding dbset properties, but wrong-sounding entity types. E.g., new Customers is a weird way to create a single customer. Singular names produce wrong-sounding dbset props, but I find that slightly less disturbing.)

Having done this, I'm not sure the approach of modifying the model feels right, because the name you want depends on where the name is actually being used - a property referring to a collection of entities of some type typically wants a different name than one referring to a single property, and some people might want yet another convention again for the mapped table name. I'd prefer the ability to supply an interface (e.g., INameMapper) with methods such as GetSingularNavigationPropertyName, GetMultipleNavigationPropertyName, GetEntityTypeName, and maybe even GetContextDbSetPropertyName.

There's already a partial implementation of this concept in RelationalScaffoldingModelFactory, which has GetEntityTypeName and GetPropertyName methods you can override. My ideal solution to this would have this fleshed out so I can control everything, and for it to be separated out, so that I'm not obliged to derive from, say, SqlServerScaffoldingModelFactory just to be able to plug in my logic. (Pluralizing/singularizing of identifiers used in code doesn't feel like it should have a dependency on a database-specific type, but as far as I can tell, I needed to make my own derived SqlServerScaffoldingModelFactory to be able to use this extensibility point.)

[jjwilliams42]

I realize this is going on 2 years old, but was anything changed here that might make customization easier?

[tonysneed]

👍 For providing customizable code gen templates (for ex, T4 or handlebars), but doing so in a way that can feed into dotnet ef scaffold, so that it's cross platform and not tied to Visual Studio.

[bricelam]

No progress yet. Our main focus for Reverse Engineering is enable updating the model to incorporate changes made to the database after the initial scaffold. #831 During update, we'll try to preserve any manual changes that have been made to the model (e.g. renames and inheritance) which mitigates some of the reasons you might be asking for this feature. But there are still plenty of other reasons to do this feature. It's just a matter of prioritization.

[tonysneed]

In #9676 @ajcvickers states you would accept a PR to add virtual methods for extensibility. If that's the case, I'd be happy to submit a PR for this.

[ajcvickers]

@tonysneed Yep. There was a PR (#9908) but it was abandoned. We would want protected virtual methods.

[bricelam]

If anyone is interested in poking around the internal components...

⚠️Warning: These will break in a future release.

class MyDesignTimeServices : IDesignTimeServices
{
    public void ConfigureDesignTimeServices(IServiceCollection services)
        => services
            .AddSingleton<ICSharpDbContextGenerator, MyDbContextGenerator>()
            .AddSingleton<ICSharpEntityTypeGenerator, MyEntityTypeGenerator>();
}

class MyDbContextGenerator : CSharpDbContextGenerator
{
    public MyDbContextGenerator(
        IScaffoldingProviderCodeGenerator providerCodeGenerator,
        IAnnotationCodeGenerator annotationCodeGenerator,
        ICSharpUtilities cSharpUtilities)
        : base(providerCodeGenerator, annotationCodeGenerator, cSharpUtilities)
    {
    }
    
    // TODO: Override DbContext generation
}

class MyEntityTypeGenerator : CSharpEntityTypeGenerator
{
    public MyEntityTypeGenerator(ICSharpUtilities cSharpUtilities)
        : base(cSharpUtilities)
    {
    }
    
    // TODO: Override entity type generation
}

[tonysneed]

I can pick this one up. Already signed a contrib agreement for ASPNET Core.

[tonysneed]

For some reason adding the user profile dotnet folder to my path system env variable doesn't seem to work.

dotnet --version doesn't see it.

However, if I replace the path entirely, it's OK.

Am I doing something obviously wrong? TIA!

P.S. I can just open the VS solution from the command line, so I can get past the issue. Just wondering about setting the global path and what I might be doing wrong there.

[tonysneed]

@bricelam So to use the overrides, would one then register IDesignTimeServices with MyDesignTimeServices in Startup.ConfigureServices?

nm .. I see how to do it in your SO answer here.

[bricelam]

That answer outdated. Just add an implementation anywhere in your project. The tools will scan the assembly to find it.

[ajcvickers]

@tonysneed Make sure the userprofile dotnet is at the start of the path so that it is found before the normally installed copy.

[bricelam]

Also, don't use %USERPROFILE% in System variables. It's ...unpredictable. 😉

[tonysneed]

@ajcvickers I'm having a hard time controlling the placement of the userprofile dotnet in the path. Adding it at the top ..

Seems to have no effect. It is placed after the system dotnet.

Not a big deal, since I can set the path on the command line and open VS from there. Just curious if I'm missing something obvious.

[ErikEJ]

I have removed the system .net path setting

[ajcvickers]

@tonysneed I think you need to set it as a system environment variable--at least, that's what I did. You can also click on Edit text.., then it's easy to put it where you want:

[tonysneed]

OK, mystery solved. I was opening the command prompt from the GitHub Desktop app, and it wasn't picking up the new environment variables -- until I restarted the app.