Loopback post request cannot filter and array

Question

I have a POST road that received an array of Queue. I want to filter them before to create them inside my data source.

I tried to do it like this:

  async createarraywithcheck(
    @requestBody(/*...*/)
    queues: [Omit<Queue, 'id'>],
  ): Promise<Queue[]> {
    queues = queues.filter(queue => queue.title.length < 10); //error here
    return this.queueRepository.createAll(queues);
}

But I get this error:

Type 'Pick<Queue, "getId" | "getIdObject" | "toJSON" | "toObject" | "title">[]' 
is not assignable to type 
'[Pick<Queue, "getId" | "getIdObject" | "toJSON" | "toObject" |"title">]'.

Target requires 1 element(s) but source may have fewer.ts(2322)

I do not understand the difference, to me they are both array of Pick<Queue, ....>.

How can I fix that?

Answer 1

As discussed, problem comes from the type of your queues argument.

You set the type as [Omit<Queue, 'id'>], which is a tuple. Not any tuple, but a tuple with exactly one argument.

In javascript, a tuple is basically an array. If you filter this array, what happens if none of the items pass the condition? well, you return an empty array. Since you are re-assigning to queues, you may be doing the following:

queues = [] // here you have the error

Solution is one of the below:

1. const filteredQueues: Omit<Queue, 'id'>[] = queues.filter(queue => queue.title.length < 10)
2. queues: Omit<Queue, 'id'>[]