How to implement a universal log system for entity changes using TypeORM & NestJS (with relations)

[wary nest]

Hi everyone 👋

I’m building a universal logging system in NestJS using TypeORM. My goal is to track and log all changes made to entities, including nested properties and relations.

What I'm currently doing:
I use a TypeORM event subscriber (afterUpdate) to hook into update events.

I compare the old value vs new value using the diff npm library.

I store the changed paths, old values, and new values for auditing purposes.

The limitation:
TypeORM only provides the updated entity in event.entity, and not the full object with its relations or nested structure.

event.databaseEntity (the previous value) also lacks full nested relation data.

To work around this, I do the following:

Manually fetch the full object with nested relations before the update using .findOne({ relations: [...] }).

After the update, fetch the new version of the object.

Compare both versions using diff.

Manually exclude fields like id, createdAt, etc. which are irrelevant for audit logging.

What I'm asking:
Is there a better, cleaner or more efficient way to do this in NestJS with TypeORM?

Specifically to get both before and after states of an entity with all nested relations inside the subscriber or elsewhere in a universal/global context.

Bonus: any way to auto-ignore non-meaningful fields like id, timestamps, etc.

Would love to hear how others solved this or approached it differently 🙏

How to implement a universal log system for entity changes using TypeORM & NestJS (with relations)

[robust scroll]

What's the motivation for creating such log?

[wary nest]

To keep track of any changes done by anyone in the application.CRUD

[robust scroll]

I understand the purpose, I'm trying to understand the reason why you need such a detailed log?

I'm afraid there's no generic tool to do this. The closest thing I know of is Debezium, that monitors your database's transaction log and streams the changes to Kafka

[wary nest]

Take a scenario
I'm tracking application's changes

i changed its statue (status_id) that is basically a uuid
in logs I want to show the actual status name not the change in UUID(foreign key)

and the motivation is self-interest and requirement of the project. The DB I'm working on is quite sensitive and needs to be tracked of any changes after once the data has been inserted

[robust scroll]

Then I recommend to explicitly create an audit logger and call it in the relevant use-cases. In the same transaction that the data change

TypeORMs listeners don't use the same transaction, and you might lose the logs

[wary nest]

I thought the same but my project has grown quite a bit So , I want something generic.
Something that can be applied globally once and for all

[robust scroll]

Audit logs are not a generic thing. They have business context, which is different for each application

You already said that you don't just need to log dumb data changes, but you need to attach meaning to them

Data change for different reasons, and only your business logic knows for which reason

Of course, you can build something generic for the scope of your project

[wary nest]

yeah , by that I meant changes of foreign keys because they are nor readable for user but i still wanna track the name(or any changed values) of that foreign relation

[wary nest]

I'm having an idea to make a generic function that accepts repo as argument
fetch 2 states (along with all of their relations)
before and after updated
compare the two
make changes logs
exclude useless info (uuid e.t.c)
save it in audit_logs

The downside is I'll have to declare it in each method but I cant see a way around it

@robust scroll Thanks a lot for your insight

[shy coral]

Doesn't your DB already have CDC?

[shy coral]

Unless you mean something diferrent by audit logs, they are generic, answering a question - who did what. Not why.

[robust scroll]

Well, they usually also contain business context and metadata relevant to certain types of actions.

You can't infer that from simple CDC