Data Persistence

So far we have avoided creating variables in the contract, because the virtual machine works in an isolated context. Everything that happens in the method will be deleted after its execution. To persist data we use objects that interface the contract with the blockchain.

import BywiseUtils, { StorageValue } from 'bywise-utils.js';
 
class HelloWorldContract {
 
    value1 = new StorageValue('some text');
    value2 = "some text";
 
    setValue1(newValue) {
        this.value1.set(newValue);
    }
 
    getValue1() { // @view
        return this.value1.get();
    }
 
    setValue1InReadMethod(newValue) { // @view
        this.value1.set(newValue);
    }
 
    setValue2(newValue) {
        this.value2 = newValue;
    }
 
    getValue2() { // @view
        return this.value2;
    }
 
    setValue2InReadMethod(newValue) { // @view
        this.value2 = newValue;
    }
}
 
BywiseUtils.exportContract(new HelloWorldContract());

In this example, the only variable that can be changed is value1 because it is an instance of StorageValue. It can also only be changed by WRITE, method with @view discards all changes.

There are three types of storable variables:

StorageValue: Storage of a variable of type any
StorageMap: Equivalent to javascript Map()
StorageList: List storage

Example StorageValue:

import BywiseUtils, { StorageValue } from 'bywise-utils.js';
 
class StorageContract {
 
    value = new StorageValue('');
 
    setValue(newValue) {
        this.value.set(newValue);
    }
 
    getValue() { // @view
        return this.value.get();
    }
}
 
BywiseUtils.exportContract(new StorageContract());

Example StorageMap:

import BywiseUtils, { StorageMap } from 'bywise-utils.js';
 
class StorageContract {
 
    value = new StorageMap('some default value');
 
    setValue(key, newValue) {
        this.value.set(key, newValue);
    }
 
    hasValue(key) { // @view
        return this.value.has(key) ? 'Yes' : 'No';
    }
 
    getValue(key) { // @view
        return this.value.get(key);
    }
 
    delValue(key) {
        this.value.del(key);
    }
}
 
BywiseUtils.exportContract(new StorageContract());

Example StorageList:

import BywiseUtils, { StorageList } from 'bywise-utils.js';
 
class StorageContract {
 
    value = new StorageList();
 
    pushValue( newValue) {
        this.value.push(newValue);
    }
 
    popValue() {
        return this.value.pop();
    }
 
    setValue(index, newValue) {
        this.value.set(index, newValue);
    }
 
    size() { // @view
        return this.value.size();
    }
 
    getValue(index) { // @view
        return this.value.get(index);
    }
}
 
BywiseUtils.exportContract(new StorageContract());

It is also possible to create composite types for example a map of lists:

import BywiseUtils, { StorageMap, StorageList } from 'bywise-utils.js';
 
class StorageContract {
 
    map = new StorageMap();
 
    pushValueByKey(key, newValue) {
        if (!this.map.has(key)) {
            this.map.set(key, new StorageList());
        }
        this.map.getStorageList(key).push(newValue);
    }
 
    getSizeByKey(key) { // @view
        if (!this.map.has(key)) {
            return '0'
        }
        return this.map.getStorageList(key).size();
    }
}
 
BywiseUtils.exportContract(new StorageContract());

Variables Token Contract Example