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Issuer API - @energyweb/issuer-api

Source code on GitHub


The Issuer API is a NestJS package that provides restful endpoints for handling certificate operations (certificate request, issuance, transfer, claiming, revoking), and persisting certificate data. You can read more about the certificate lifecycle here.

The below gives an overview the of the package architecture, however the NestJS documentation provides further detail into the fundamentals of NestJS Architecture that may help to understand the elements of this application:

Issuer API Architecture

The Issuer API package is broken down into three NestJS modules:

Each module contains code relevant for a specific feature. In general, each NestJS module has:

  • A controller that manages requests and responses to the client
  • An .entity file that maps an entity to a database repository
  • A .service file that provides methods to fetch and transform data
  • Data Transfer Object (DTO) file(s) that provide Data Transfer Objects, which are representations of the data that are exposed to the endpoint consumer
  • A module class that is used by NestJS to structure the application


The Issuer API uses PostgreSQL for persistence with TypeORM as a database integration library. The application creates a repository for each entity. Entities are defined in the .entity.ts file in each module, and are marked with the @Entity decorator. (You can read more about entities in the TypeORM documentation here).

export class CertificationRequest extends ExtendedBaseEntity implements CertificationRequestDTO {
    id: number;

    owner: string;

    @Column('varchar', { nullable: false })
    energy: string;

    deviceId: string;


Repositories are injected into services or command handlers so they are available to use in methods:

export class ApproveCertificationRequestHandler
    implements ICommandHandler<ApproveCertificationRequestCommand>
    private readonly logger = new Logger(;

        private readonly repository: Repository<CertificationRequest>,




Source code on GitHub

The blockchain module provides services to fetch and create blockchain properties, which are needed to establish connection with the blockchain through a web3 provider, and interact with smart contracts on the blockchain.

export interface IBlockchainProperties {
    web3: providers.FallbackProvider | providers.JsonRpcProvider;
    registry: RegistryExtended;
    issuer: Issuer;
    privateIssuer?: PrivateIssuer;
    activeUser?: Signer;


The BlockchainProperties entity contains a wrap method that provides new instances of the Registry and Issuer contracts with the current Signer:

    wrap(signerOrPrivateKey?: Signer | string): IBlockchainProperties {
        const web3 = getProviderWithFallback(
            ...[this.rpcNode, this.rpcNodeFallback].filter((url) => !!url)
        const assure0x = (privateKey: string) =>
            privateKey.startsWith('0x') ? privateKey : `0x${privateKey}`;

        let signer: Signer;

        if (signerOrPrivateKey) {
            signer =
                typeof signerOrPrivateKey === 'string'
                    ? new Wallet(assure0x(signerOrPrivateKey), web3)
                    : signerOrPrivateKey;
        } else {
            signer = new Wallet(assure0x(this.platformOperatorPrivateKey), web3);

        return {
            registry: Contracts.factories.RegistryExtendedFactory.connect(this.registry, signer),
            issuer: Contracts.factories.IssuerFactory.connect(this.issuer, signer),
            privateIssuer: this.privateIssuer
                ? Contracts.factories.PrivateIssuerFactory.connect(this.privateIssuer, signer)
                : null,
            activeUser: signer


The blockchain facades use the wrap method to create new instances of smart contracts when the certificate is created:

        if (!isPrivate) {
            return await CertificateFacade.create(


The blockchain properties controller manages requests and responses to the client. The service provides methods to fetch and persist the blockchain property data to the repository.

The Data Transfer Object (DTO) file provides a representation of the data that is exposed to the endpoint consumer of the controller methods.

The module file is used by NestJS to structure the application.


Source code on GitHub

The certificate module provides services to manage the certificate lifecycle after issuance (fetch, claim, transfer, issue). It has a seperate controller and commands/command handlers for batch operations (handling multiple certificates at once).

The certificate controller manages requests and responses to the client. This module uses commands and command handlers to perform business logic and persist data, rather than a service provider. To do this the module uses the NestJS CQRS (Command and Query Responsibility Segregation) module. Commands are classes that take in defined parameters. Every command has a corresponding command handler that performs business logic and persistence much like a service, using the parameters from the command. You can read more about the NestJS CQRS module in their documentation here.

The certificate module has commands and corresponding command handlers for each certificate (or batch certificate) operation (i.e. batch claim certificate, create certificate, get certificate, claim certificate, etc.)

On-chain Certificate Listener

Source code on GitHub

The OnChainCertificateWatcher class listens for events in the Registry contract (i.e. certificate creation, certificate transfer, claiming of a certificate), and publishes corresponding events for the Issuer API's command handlers to react to. This ensures that all events that occur on-chain are reflected in the database repositories.

Listen for Certificate Issuance:

    this.registry.filters.IssuanceSingle(null, null, null),
    (event: providers.Log) => this.processEvent(BlockchainEventType.IssuanceSingle, event)


Process the event and trigger the CertificatesCreated event handler:

    case BlockchainEventType.IssuanceSingle:
        logEvent(BlockchainEventType.IssuanceSingle, [event._id.toNumber()]);
        this.eventBus.publish(new CertificatesCreatedEvent([event._id.toNumber()]));



Source code on GitHub

The certification-request module manages fetching, creating and approving certificate requests. It uses the same command handler (CQRS) pattern as the certificate module.

Certificate Persistence

Certificate data is persisted in two locations:

  1. On the blockchain in the form of an ERC-1888 Transferable Certificate. Read more about this in the Issuer documentation here.
  2. In a relational database as a Certificate entity. Origin’s reference implementation uses PostgreSQL, however other registries can be used according to implementation needs.

The Issuer API uses a database to persist certificate data because it is more performant than the blockchain for data storage and data fetching.

When a certificate is requested, issued, or updated (i.e. if it has been transferred, claimed or revoked), this is reflected in the certificate’s record in the database as well as on the blockchain. The Issuer API makes updates to the Certificates on the blockchain using the Blockchain facade methods, and queries the database repository using a connection through TypeORM.

See the code snippet below from the CreateCertificateRequestHandler class. The certificate is first created on the blockchain using the CertificationRequest facade, and then created in the database using the repository service.

async execute({
   }: CreateCertificationRequestCommand): Promise<CertificationRequestDTO> {
       if (!isAddress(to)) {
           throw new BadRequestException(
               'Invalid "to" parameter, it has to be ethereum address string'

       const blockchainProperties = await this.blockchainPropertiesService.get();

       //Create Certificate on the blockchain using the blockchain facade: 

       try {
           const certReq = await CertificationRequestFacade.create(
               `Certification request ${} has been deployed with id ${} `

        //Create instance of the Certificate in the database:

           const certificationRequest = this.repository.create({
               approved: false,
               revoked: false,
               isPrivate: isPrivate ?? false,
               owner: getAddress(to)

       } catch (e) {
               `Certification request creation has failed with the error: ${e.message}`