Separate item system and effect system, don't mix them up.

The effect system manages a collection of effects.
Each effect has a unique ID (the ID can be either string or integer, whatever), and implement an interface, e.g IEffect.
IEffect has a function, something like, void perform(Item * item);
When you add new effect, just implement IEffect and add the interface to effect system.

The item system manages a collection of items.
The items can be read from database, or added by code.
An item holds a collection of effect IDs.
When you want to do the effect, just ask the effect system with the effect ID, and the call IEffect::perform with the given item.

With this design, your item only knows an effect ID. It doesn't care what's the effect, or how effect works.

Separate item system and effect system, don't mix them up.

The effect system manages a collection of effects.
Each effect has a unique ID (the ID can be either string or integer, whatever), and implement an interface, e.g IEffect.
IEffect has a function, something like, void perform(Item * item);
When you add new effect, just implement IEffect and add the interface to effect system.

The item system manages a collection of items.
The items can be read from database, or added by code.
An item holds a collection of effect IDs.
When you want to do the effect, just ask the effect system with the effect ID, and the call IEffect::perform with the given item.

With this deisng, your item only knows an effect ID. It doesn't care what's the effect, or how effect works.