How to track changes of an object in exonum

Question

I have one object in my blockchain and my application keeps updating it regularly. I want to keep track of the 
changes that happen to the object. Below is a part of my code.

encoding_struct! {
    struct AC {
        const SIZE = 16;
        field s: Vec<u32> [00 => 08]
        field o: Vec<u32> [08 => 16]
    }
}

i have transaction with empty init

message! {
    struct TxInitAC {
        const TYPE = SERVICE_ID;
        const ID = TX_INIT_AC;
        const SIZE = 0;
    }
}

and i have an execute method

fn execute(&self, view: &mut Fork) {
    let mut schema = CurrencySchema { view };                   
    let ac = AC::new(vec![], vec![]);        
    schema.access_control().push(ac);
}

Answer 1

You have to describe each component in a corresponding encoding_struct! to describe a compound object.

you can do it like this:
encoding_struct! {
    struct Pair {
        const SIZE = 8;
        field s: u32 [00 => 04]
        field o: u32 [04 => 08]
    }
}

encoding_struct! {
    struct AC {
        const SIZE = 8;
        field inner : Vec<Pair> [00 => 08]
    }
}

then initialize the blockchain db like this:

impl Service for MService {
//...
    fn initialize(&self, fork: &mut Fork) -> Value {
        let mut schema = MatrixSchema { view: fork };
        let matrix = AC::new(vec![]);
        // assume method ac() is implemented for the schema
        schema.ac().set(ac);        
        Value::Null
    }
}