injecting service into decorator

[cosmic sierra]

I need to create decorator which will be used to generate traces, to do so I will need an external service injected in this decorator - what's the recommended way of doing such thing? can I somehow simply inject service into decorator?

[stone cloud]

I think you are looking for Interceptors : https://docs.nestjs.com/interceptors

[cosmic sierra]

I don't think so - I want to trace just a single method not a whole request

[wicked spindle]

you could set a metadata key for the decorated method and on startup wrap all methods that have this metadata with a trace function

[gleaming flume]

While it's not possible to inject a service into a decorator, you can take a method decorator and modify the descriptor.value to reference the class's injected values. I have an example of this with my ogma package where I provide a @Log() method that printed a log at the beginning and end of the method for tracing purposes

[tribal steppe]

@gleaming flume Could you share a link for that please ?

[gleaming flume]

https://github.com/jmcdo29/ogma/blob/main/packages/nestjs-module/src/decorators/ogma-logger.decorator.ts#L25

[crystal hemlock]

@cosmic sierra If you need to generate traces, just go with OTEL. There's no point in inventing a custom solution. https://www.npmjs.com/package/nestjs-otel

[tribal steppe]

Thank you very much 🙏

[cosmic sierra]

ok, I agree with traces, but there's probably no "standardized" way of measuring time of execution of some method for metrics purposes, correct? so the only way is to write some custom decorator

[crystal hemlock]

I think otel can do metrics this way too, let me check

@OtelHistorgram might do that