Metadata

Metadata of the project

Overview

Subsembly runtimes expose metadata to make the interaction easier. Each module's own metadata together form one general metadata of a blockchain. Metadata of the module provides all the necessary information about the module.

Module Metadata

Module metadata has five properties, each holding a list of module specific items:

• calls - dispatchable extrinsic calls

• storage items - list of module specific storage entries

• events - list of module specific events

• constants - list of module specific constants

• errors - list of module specific well-known errors

Metadata Encoding

Subsembly metadata encoding follows the same rules as Substrate Metadata.

Metadata Generation

One of the preliminary steps of runtime compilation is to generate metadata and dispatcher files. This is achieved by parsing module files and runtime.ts file to populate metadata of the module.

For example, storage items of each module are located in the beginning of the module file:

// balances.ts

export namespace BalancesStorageEntries{
    /**
     * @description Stores information about accountId
     * @storage_map AccountId
     */
    export function Account(): StorageEntry<Balance>{
        return new StorageEntry<Balance>("Balances", "Account");
    }
}

Extrinsic calls are parsed from the static functions of the declared modules. The following static function is parsed as an extrinsic call for Balances module.

    /**
     * @description Transfer the given value from source to destination
     */
    static transfer(source: AccountIdType, dest: AccountIdType, value: Balance): u8[] {
     // Logic of the function //
    }

Static function with a name starting with underscore (_) is ignored while parsing and considered as internal function.

And constants for each module are declared inside the runtime.ts:

For instance, constants for Timestamp are declared like this:

/**
 * @description Types and constants used in Timestamp pallet
 */
export class TimestampConfig {
    /**
     * @description Minimum period between timestamps
     */
    static minimumPeriod(): Moment {
        return instantiate<Moment>(5000);
    }
}