Retrieval of related model for a HasMany relation

[b-admike]

Description

Follow up for #1342. Given Customer and Order models, and a customer that has orders already, I would like to define a HasMany relation and

• find all the orders for said customer in a controller method
• create an order for said customer in a controller method

Acceptance Criteria

• Infer relation metadata from the hasMany decorator to construct constrained target repository instance on relational property
• Create a calculated property on the source repository (CustomerRepository in this case) which returns a constrained target repository (for e.g. customerRepo.<decorated_property_name or relation_name>.update(...)) using the relation metadata and supplied constraint in the controller method

Code snippet for UX:

export class CustomerController {
  constructor(
    @repository(CustomerRepository) protected customerRepo: CustomerRepository,
    @repository(OrderRepository) protected orderRepo: OrderRepository
  ) {}

  async function getCustomerOrders(customerId: number): Promise<Order[]> {
    return await customerRepo.orders({id: customerId}).find();
  }

 async function createCustomerOrders(customerId: number, orderData: Partial<Order>): Promise<Order> {
    return await customerRepo.orders({id: customerId}).create(orderData);
  }
  }

export class CustomerRepository {
  // We should be able to inject a factory of OrderRepository by name or instance
  // and infer `Order` from the `OrderRepository`
  @hasMany('orderRepository');  // The argument can be an object to pass in more info
  public readonly orders: (key: Partial<Customer>) => OrderRepository;
  }

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[dhmlau]

It corresponds to the first 2 points from #1032 (comment):

1. HasMany with a single operation find, covering both repository/persistence and REST API in a controller method.
2. Add create method to repository/persistence layer and expose it in REST API as a new controller method.

[raymondfeng]

Here is what I have in mind:

export class CustomerRepository {
  // We should be able to inject a factory of OrderRepository by name or instance
  // and infer `Order` from the `OrderRepository`
  @hasMany('orderRepository');  // The argument can be an object to pass in more info
  public readonly orders: (key: Partial<Customer>) => OrderRepository;
  }

async function getCustomerOrders(customerId: number): Promise<Order[]> {
    return await customerRepo.orders({id: customerId}).find();
}

[jannyHou]

@b-admike a question for the code snippet:

export class CustomerController {
  constructor(
    @repository(CustomerRepository) protected customerRepo: CustomerRepository,
    @repository(OrderRepository) protected orderRepo: OrderRepository
  ) {}

  async function getCustomerOrders(customerId: number): Promise<Order[]> {
    return await customerRepo.orders.find(customerId, orderRepo);
  }

 async function createCustomerOrders(customerId: number, orderData: Partial<Order>): Promise<Order> {
    return await customerRepo.orders.create(customerId, orderData, orderRepo);
  }
  }

Does it mean we automatically get the related property customerRepo.orders by:

• add relation in model def of Customer and Order
• instintiate customerRepo and orderRepo in the controller class's constructor
  ?

[b-admike]

Does it mean we automatically get the related property customerRepo.orders by:
add relation in model def of Customer and Order
instintiate customerRepo and orderRepo in the controller class's constructor?

@jannyHou yeah that's correct.

[bajtos]

See also #1353

[b-admike]

Closing as #1438 has landed.