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

skyslide22 · 2023-06-14T20:06:40.831Z

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 ```cs [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

T

Thinker•6/14/23, 8:06 PM

You can't

T

Thinker•6/14/23, 8:07 PM

actually no you can but it takes the power of literal black magic

T

Thinker•6/14/23, 8:08 PM

Bottom line is that Python-like decorators just aren't supported in regular C#.

J

Jimmacle•6/14/23, 8:08 PM

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?

S

Sossenbinder•6/14/23, 8:09 PM

This is probably a task for source generators or dynamic codegen

S

Sossenbinder•6/14/23, 8:09 PM

Not sure what python does to make this work

S

skyslide22OP•6/14/23, 8:09 PM

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

T

Thinker•6/14/23, 8:09 PM

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

S

Sossenbinder•6/14/23, 8:09 PM

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

Sskyslide22 i got 100 database "middlewares" where i just want to add attributes to catch ex...

T

Thinker•6/14/23, 8:09 PM

Then you should probably do that using middleware/filters

S

Sossenbinder•6/14/23, 8:10 PM

So the code needs to be in a specific layout

J

Jimmacle•6/14/23, 8:10 PM

this would be IL weaving

J

Jimmacle•6/14/23, 8:10 PM

if anything

T

Thinker•6/14/23, 8:10 PM

yeah, black magic

S

Sossenbinder•6/14/23, 8:10 PM

Yeah, that's going to work for everything

S

Sossenbinder•6/14/23, 8:10 PM

I'd put source gen a level lower on the magic scale at least, but it won't work everywhere

S

skyslide22OP•6/14/23, 8:11 PM

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);
        }
    }
}

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);
        }
    }
}

S

skyslide22OP•6/14/23, 8:12 PM

take a look at the last method

T

Thinker•6/14/23, 8:12 PM

wtf are these type and parameter names kekw

S

skyslide22OP•6/14/23, 8:12 PM

we got a code generator ^^

J

Jimmacle•6/14/23, 8:13 PM

make the code generator follow standard C# guidelines peepo

S

skyslide22OP•6/14/23, 8:13 PM

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

T

Thinker•6/14/23, 8:18 PM

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

S

skyslide22OP•6/14/23, 8:31 PM

for models, yes

S

skyslide22OP•6/14/23, 8:32 PM

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

J

Jimmacle•6/14/23, 8:33 PM

i'm glad i just use efc

TThinker actually no you *can* but it takes the power of literal black magic

M

Mayor McCheese•6/14/23, 8:40 PM

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

M

Mayor McCheese•6/14/23, 8:41 PM

Assuming black magic is il weaving

T

Thinker•6/14/23, 8:42 PM

hmm, how would you do it otherwise?

T

Thinker•6/14/23, 8:42 PM

like... replace the method IL at runtime?

J

Jimmacle•6/14/23, 8:44 PM

one of my old game projects made liberal use of runtime IL emission and monkey patching

J

Jimmacle•6/14/23, 8:45 PM

https://github.com/TorchAPI/Torch/tree/master/Torch/Managers/PatchManager it's basically harmony from before harmony added a bunch of features

J

Jimmacle•6/14/23, 8:46 PM

also i didn't write it so don't ask me questions about it when

TThinker hmm, how would you do it otherwise?

M

Mayor McCheese•6/14/23, 8:46 PM

Some di frameworks support interception, with absurd performance costs

T

Thinker•6/14/23, 8:47 PM

Would love to see how that is done

TThinker Would love to see how that is done

M

Mayor McCheese•6/14/23, 8:47 PM

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

S

Sossenbinder•6/14/23, 8:47 PM

Doesn't that use something like Castle DynamicProxies?

M

Mayor McCheese•6/14/23, 8:48 PM

Yes

M

Mayor McCheese•6/14/23, 8:51 PM

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

S

skyslide22OP•6/14/23, 8:56 PM

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);
        }

        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);
        }

M

Mayor McCheese•6/14/23, 8:59 PM

I'm not remotely a fan

M

Mayor McCheese•6/14/23, 8:59 PM

You're going to swallow exceptions because it's prod??

J

Jimmacle•6/14/23, 9:00 PM

sounds like a bad idea

J

Jimmacle•6/14/23, 9:00 PM

log them at minimum

S

skyslide22OP•6/14/23, 9:02 PM

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

M

Mayor McCheese•6/14/23, 9:02 PM

So do that with an exception handler

S

skyslide22OP•6/14/23, 9:02 PM

default(T) is probably not the best solution

M

Mayor McCheese•6/14/23, 9:02 PM

Is this aspnet core?

S

skyslide22OP•6/14/23, 9:03 PM

blazor wasm api yes

M

Mayor McCheese•6/14/23, 9:04 PM

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

Handle errors in ASP.NET Core

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

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