Dot Code School Suggestion: Feedback for Section 1 - Chapter 3: Substrate Storage

[benjaminsalon]

Hey @philoniare, I think this part about the ValueQuery is not true:

https://github.com/philoniare/polkadot-sdk-tutorial-dex/blob/b4611fc2ec6dbae147f15f46e05d0db99778e6ed/README.md?plain=1#L22

The ValueQuery is there to define the default behavior of the storage when we try to get something with an unexisting key. You can check here: https://paritytech.github.io/polkadot-sdk/master/frame_support/storage/types/trait.QueryKindTrait.html

[shawntabrizi]

yes, this is correct.

The way i would explain value query is to go a little deeper in general:

• in a DB, storage is always an option: there is either Some value at a key, or there is None value at a key.
• the default behavior for accessing storage is OptionQuery which exposes exactly that information to you the developer
• there are scenarios where you want None to actually represent some value, the common example is Balance where None is exactly the same as having 0 balance. In this case, you would probably rather handle 0 than an option each time you query and use a balance.
• value query will return the default value for a type when the value is None and can be used in scenarios like this.
• to adjust the value returned by value query, you can also adjust the defaultvalue parameter or whatevr it is called

[philoniare]

@benjaminsalon @shawntabrizi Thanks for pointing it out guys. Updated