Convert Result<Option<T> > into struct

Technical Discussion
#1

How can I convert the type returned value from hdk::get_entry(&address) into struct without parsing data to end-user.

I’m a beginner in Rust and hope anybody help me in this.

Thank you

#2

Hello @Rzan and welcome to the forum! Let’s see if I understand you correctly: hdk::get_entry(&address) returns a ZomeApiResult<Option<Entry>> but you actually want the return value to be in the Rust type that it was when you committed the entry, right?

If that’s true, then there’s a helper function called hdk::util::get_as_type(). If you use this function, it’ll convert automatically back into the Rust struct. Note that you do have to specify which type of struct; Holochain isn’t yet smart enough to figure that out for you based on the entry type. So it would look like:

let person = hdk::util::get_as_type<Person>(&person_address)?;

(@freesig please check my Rust code cuz I am still so green :smiley: )

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#3

I’m really grateful @pauldaoust, it is exactly what I’m looking for :+1:

The syntax like this
let person = get_as_type::<Person>(&person_address)?;

I added also these two lines ::

#![feature(try_from)]
use std::convert::TryFrom;

#4

If you are just returning that person you can also just do:

get_as_type::<Person>(&person_address)

on the last line :slight_smile:

#5

I love learning stuff from the people I’m trying to help out. Thanks @Rzan for showing me the proper syntax, reminding me you need TryFrom, and @freesig for showing how you can do some magical type conversion (I still have no clue about when casts and conversions need to be explicit).

#6

Actually if your function returns ZomeApiResult<Person> then you don’t need the ::<Person>.
So it could just be:

fn retrieve_person(address: Address) -> ZomeApiResult<Person> {
    hdk::utils::get_as_type(address)
}
1 Like