Writing a 'database' in ECS

Currently, my items are read from a XML and written in many Dictionaries. It's literally ECS but with none of the advantages. Why I did like that? Because it's easy to know if they exist, I can access from anywhere, works at edit time, can have sprites and strings (etc etc, probably will be replaced with pure ECS when it finally releases fully featured).
What I want to know, is how to convert that into ECS during runtime, with the 'best strategy', so I can get the best of both worlds.

Some context to clarify:
All item descriptors (names, weight, icon, etc) are stored in plenty of Dictionaries across many classes and indexed by a long key, so that it's easy to mod a new property, like volume.
All item instances are in ECS, same with containers.
All item operations (move to container, consume, destroy) will, hopefully, run in ECS

So what I want to, is to copy the relevant bits of information in those dictionaries into ECS, but I am unsure the best strategy for that. I assume it's something to do with those ISharedComponentData.
Currently, most operations, when a item information is needed, like weight, would query a Dictionary for said information. I could ensure that the long identifiers are all sequential and replace the Dictionaries with arrays, but the best possible scenario would be to use those nifty cache-miss-avoiding-mathmagics from ECS.

So I'd like to know, what are the best strategies to use when possible, and least worse to use otherwise

 

I will ask just in case, you are aware, that ECS itself don't handle strings, if you go beyond dictionary <string, type> etc.?

But if your DB handles only numeric values, then buffer arrays could be good way to go.

 

I am aware that ECS don't handle strings, which is why it was easier to load stuff to Dictionary for now.
I guess i will just go with arrays then, I assumed there was a "right" way rather than static arrays

 

If you use NativeHashMap/MultiHashMap instead of Dictionary you can take them to the job.

 

Isn't hash map inherently bad access speed compared to arrays?
Well, since it's native and managed by the ECS, it might end up with faster access than a static array