Single responsibility principle - importer

Question

I'm writing an importer, it should fetch some data from the database and put that data into appropriate places.

Now the question is, should the importer itself fetch that data, or should that data(to import) be passed to the importer and database fetching would be done outside?

What's a better way to design this?

Answer 1

If the importer does the whole job, it has to know

1. Where the data is located in the database.

2. What the "appropriate places" in your application are.

Theoretically, both of these could change independently from each other. So theoretically it is a violation of SRP.

Still I would probably not split the importer into two classes. Database schemes tend to be relatively stable, and why should the places where you have to put the data change? Therefore splitting things up sounds like overengineering to me.

Abstraction is very helpful if you actually make use of it. But it also comes at a cost.

Of course as always it depends on the specific case and you did not provide much background information.

Answer 2

There is an already accepted answer, but I do have a different opinion - when both loading from one source medium and saving to another target medium are not trivial.

For instance take reading an Excel and storing in a database.

Excel Reader class

One can create an Excel reader with which to traverse the table rows, check the correct column titles, convert date/time values, deal with the last "half" row. Maybe pass a Map of defined columns with their own customizable data validation and conversion.

This class can nicely be unit tested and decoupled of the specific import usage.

Top Importer class (controller?)

The main importing class could have an Excel reader field and do a specific import, storing the values.

Writing to the database could be a separate concern, but I believe that the database beans will be extended to have adequate inserts and all.

The repository bean(s) of the database

One may consider the injected repository beans, as fields of the importer class are also a form of separating responsibilities.

Conclusion

What one would not like to have is one loop reading and writing, with special handling on both sides.

Also unit tests are much easier, one might store sample data. Test Driven Development is possible.

And finally maybe simpler code and code reuse are now feasible.