C#•2y ago

❔ Python Decorators in C# ??? How do i intercept method calls with attributes?

Is is possible to intercept/prevent a method call in c# with attributes? i was thinking about something like python decorators, which can decide what happens with the method call, args and return value

[ThrowIfIdMatches("id", 69)]
public string MyMethod(int id)
{
  return "my id is " + id
}

[ThrowIfIdMatches("id", 69)]
public string MyMethod(int id)
{
  return "my id is " + id
}

that should throw a ValueError if the id parameter is 69, for example

45 Replies

Thinker•2y ago

You can't actually no you can but it takes the power of literal black magic Bottom line is that Python-like decorators just aren't supported in regular C#.

Jimmacle•2y ago

if you have the ability to add an attribute to the method you also have the ability to add code that does the same thing, no?

Sossenbinder•2y ago

This is probably a task for source generators or dynamic codegen Not sure what python does to make this work

skyslide22OP•2y ago

i got 100 database "middlewares" where i just want to add attributes to catch exceptions if env.IsDevelopment() for example

Thinker•2y ago

SGs can't do this because they can't modify source

Sossenbinder•2y ago

Yeah that's true, they'd have to put a decorator around

Thinker•2y ago

Then you should probably do that using middleware/filters

Sossenbinder•2y ago

So the code needs to be in a specific layout

Jimmacle•2y ago

this would be IL weaving if anything

Thinker•2y ago

yeah, black magic

Sossenbinder•2y ago

Yeah, that's going to work for everything I'd put source gen a level lower on the magic scale at least, but it won't work everywhere

skyslide22OP•2y ago

this is what we do at the moment

namespace Application.Logic
{
    public class AppLogic
    {
        private readonly Database _database;
        private readonly EmailSender _emailsender;
        private readonly BlobStorage _blobStorage;
        private readonly QMessageHandler _qMessageHandler;

        //Inject all services that will be used by logic layer
        public AppLogic(Database database, EmailSender emailsender, BlobStorage blobstorage, QMessageHandler qmessagehandler)
        {
            _database = database;
            _emailsender = emailsender;
            _blobStorage = blobstorage;
            _qMessageHandler = qmessagehandler;
        }

        public IEnumerable<procVermieterSelectGridAll_Results> procVermieterSelectGridAll()
        {
            return _database.procVermieterSelectGridAll();
        }
        public procVermieterSelect_Results? procVermieterSelect(procVermieterSelect_InputParams procVermieterSelect_InputParams)
        {
            return _database.procVermieterSelect(procVermieterSelect_InputParams).FirstOrDefault();
        }
        public IEnumerable<procFranchisorAll_Results> procFranchisorAll()
        {
            return _database.procFranchisorAll();
        }
        public IEnumerable<proccboshopsall_Results> proccboshopsall()
        {
            return _database.proccboshopsall();
        }
        public IEnumerable<Rents_PaidSelectList_Results> Rents_PaidSelectList(Rents_PaidSelectList_InputParams Rents_PaidSelectList_InputParams)
        {
            return _database.Rents_PaidSelectList(Rents_PaidSelectList_InputParams);
        }

        [ThrowIfInDevelopmentElse(null)]
        public async Task<int?> Rents_PaidInsert(Rents_PaidInsert_InputParams Rents_PaidInsert_InputParams)
        {
            return await _database.Rents_PaidInsert(Rents_PaidInsert_InputParams);
        }
    }
}

namespace Application.Logic
{
    public class AppLogic
    {
        private readonly Database _database;
        private readonly EmailSender _emailsender;
        private readonly BlobStorage _blobStorage;
        private readonly QMessageHandler _qMessageHandler;

        //Inject all services that will be used by logic layer
        public AppLogic(Database database, EmailSender emailsender, BlobStorage blobstorage, QMessageHandler qmessagehandler)
        {
            _database = database;
            _emailsender = emailsender;
            _blobStorage = blobstorage;
            _qMessageHandler = qmessagehandler;
        }

        public IEnumerable<procVermieterSelectGridAll_Results> procVermieterSelectGridAll()
        {
            return _database.procVermieterSelectGridAll();
        }
        public procVermieterSelect_Results? procVermieterSelect(procVermieterSelect_InputParams procVermieterSelect_InputParams)
        {
            return _database.procVermieterSelect(procVermieterSelect_InputParams).FirstOrDefault();
        }
        public IEnumerable<procFranchisorAll_Results> procFranchisorAll()
        {
            return _database.procFranchisorAll();
        }
        public IEnumerable<proccboshopsall_Results> proccboshopsall()
        {
            return _database.proccboshopsall();
        }
        public IEnumerable<Rents_PaidSelectList_Results> Rents_PaidSelectList(Rents_PaidSelectList_InputParams Rents_PaidSelectList_InputParams)
        {
            return _database.Rents_PaidSelectList(Rents_PaidSelectList_InputParams);
        }

        [ThrowIfInDevelopmentElse(null)]
        public async Task<int?> Rents_PaidInsert(Rents_PaidInsert_InputParams Rents_PaidInsert_InputParams)
        {
            return await _database.Rents_PaidInsert(Rents_PaidInsert_InputParams);
        }
    }
}

take a look at the last method

Thinker•2y ago

wtf are these type and parameter names kekw

skyslide22OP•2y ago

we got a code generator ^^

Jimmacle•2y ago

make the code generator follow standard C# guidelines peepo

skyslide22OP•2y ago

those are old database table names etc, can not change that

Thinker•2y ago

you use database table names for type names...?

skyslide22OP•2y ago

for models, yes our code generator creates c# classes from mssql database tables based on stored procedures for insert, select, update, delete, selectList

Jimmacle•2y ago

i'm glad i just use efc

Mayor McCheese•2y ago

Well you can do it without black magic, but it's extremely expensive performance wise Assuming black magic is il weaving

Thinker•2y ago

hmm, how would you do it otherwise? like... replace the method IL at runtime?

Jimmacle•2y ago

one of my old game projects made liberal use of runtime IL emission and monkey patching https://github.com/TorchAPI/Torch/tree/master/Torch/Managers/PatchManager it's basically harmony from before harmony added a bunch of features also i didn't write it so don't ask me questions about it when

Mayor McCheese•2y ago

Some di frameworks support interception, with absurd performance costs

Thinker•2y ago

Would love to see how that is done

Mayor McCheese•2y ago

https://autofac.readthedocs.io/en/latest/advanced/interceptors.html

Sossenbinder•2y ago

Doesn't that use something like Castle DynamicProxies?

Mayor McCheese•2y ago

Yes And castle DP is a bit of a perf nightmare, couple that with transient DI, it can get nasty

skyslide22OP•2y ago

i think this solves my problem

        public async Task<TResult?> ThrowIfNotProduction<TResult, TArg>(Func<TArg, Task<TResult>> func, TArg arg)
        {
            try
            {
                return await func(arg);
            }
            catch
            {
                if(_env.IsDevelopment())
                    throw;
            }
            return default;
        }
// and then
        public async Task<int?> Rents_PaidInsert(Rents_PaidInsert_InputParams Rents_PaidInsert_InputParams)
        {
            return await ThrowIfNotProduction(_database.Rents_PaidInsert, Rents_PaidInsert_InputParams);
        }

        public async Task<TResult?> ThrowIfNotProduction<TResult, TArg>(Func<TArg, Task<TResult>> func, TArg arg)
        {
            try
            {
                return await func(arg);
            }
            catch
            {
                if(_env.IsDevelopment())
                    throw;
            }
            return default;
        }
// and then
        public async Task<int?> Rents_PaidInsert(Rents_PaidInsert_InputParams Rents_PaidInsert_InputParams)
        {
            return await ThrowIfNotProduction(_database.Rents_PaidInsert, Rents_PaidInsert_InputParams);
        }

Mayor McCheese•2y ago

I'm not remotely a fan You're going to swallow exceptions because it's prod??

Jimmacle•2y ago

sounds like a bad idea log them at minimum

skyslide22OP•2y ago

i want to return null to the frontend if an exception is raised in prod

Mayor McCheese•2y ago

So do that with an exception handler

skyslide22OP•2y ago

default(T) is probably not the best solution

Mayor McCheese•2y ago

Is this aspnet core?

skyslide22OP•2y ago

blazor wasm api yes

Mayor McCheese•2y ago

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/error-handling

Handle errors in ASP.NET Core

Discover how to handle errors in ASP.NET Core apps.

Mayor McCheese•2y ago

Do you mean you have an api machine in wasm? Or you have a server side api you call?

skyslide22OP•2y ago

server side api

Mayor McCheese•2y ago

I'd just use a global exception handler than try and muddy up the works

skyslide22OP•2y ago

my goal is to get rid of try catch in every method, i was thinking about a wrapper which handles the exceptions and may return null on production, with logging or email sending

Mayor McCheese•2y ago

Just use the global exception handler and only add the middleware in prod The handler will grab the exception and you decide how to handle it and pass back whatever you want You can write your own middleware too if you want Just don't make your code a hot mess of environment proxy wrappers everywhere.

Thinker•2y ago

kinda, yeah, but that's not implemented yet

Mayor McCheese•2y ago

Which?

cap5lut•2y ago

probably the interceptor proposal: https://github.com/dotnet/csharplang/issues/7009

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Python Decorators in C# ??? How do i intercept method calls with attributes?