Spring4D, DI and attribute inject

[Jacek Laskowski 57]

I now do the injection by the constructor, but this causes some constructors to be very complex.

Is injecting by [inject] attribute directly into the object field a good practice? Is it better not to do it?

[Stefan Glienke 2002]

No, it's not a good practice - write your classes in a way that you could do pure DI.

If you do field injection that code can't run without a DI container or some other ways to do such injection.

 

If you have too many ctor arguments you are suffering from so called constructor over-injection and there is a way to solve this:

refactor your code and respect the single responsibility principle - see https://blog.ploeh.dk/2010/02/02/RefactoringtoAggregateServices/

 

Always think of a DI container as something like an automated assembling plant - all the screws and pieces that are put together there by robots don't know of the assembling plant.

You can as well grab a screwdriver or some other tool yourself and put the pieces together manually with a lot of work and sweat but it's possible.

Edited October 22, 2019 by Stefan Glienke