Pick could reorder

[mariusrak]

Hi, if I use .pick() on schema it could reorder fields by order given in the pick call not by original order.

[github-actions]

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[aldeed]

@mariusrak Have you checked to see whether other pick functions such as lodash preserve the order?

Also, JavaScript prior to ES2015 doesn't guarantee object key iteration order for any objects, and even with ES2015 it is not 100% guaranteed. So I generally wouldn't rely on it.

That being said, a few aspects of SimpleSchema do act differently depending on key order, and in general I believe a schema object would always have a guaranteed key iteration order with ES2015.

I am not sure whether I think this should be "fixed", though. If pick were updated to keep the same order, it would be impossible to pick keys in a different order. Right now, you can pick in the same order or a new order by choosing how you order the key names in the array. So maybe this just needs to be documented but not changed?

[mariusrak]

I'm not sure whether I understand. I wanted to pick keys in different order, but even when I provided keys in order different than in original schema, they were ordered by original schema not by new order.

[aldeed]

Oh I see. Your description sounded like a bug report but you are requesting a feature.

[mariusrak]

Well originally I thought it is a feature request. But you wrote

Right now, you can pick in the same order or a new order by choosing how you order the key names in the array. So maybe this just needs to be documented but not changed?

So I'm not sure how it should work. Maybe I'm just using it wrong. I use the simple-schema with uniforms package. I have schema from fields e.g.

{field1: String, field2: String, field3: String}

and I do

schema.pick('field3', 'field1')

I expect to see form with field3 first and field1 second. But they are ordered as was originally defined. This contradicts your claim. So I guess we did not understood each other?

[aldeed]

@mariusrak No I wrote that from memory without checking. It does preserve the original order. I think the best solution to avoid any breaking changes would be to keep pick as is and add a pickInNewOrder (or whatever name people like) method that does what you are asking for.

In the meantime, you could write your own with something like this:

function pickInNewOrder(schema, ...fields) {
  const newSchema = {};

  for (const field of fields) {
    for (const key of this._schemaKeys) {
      if (key === field || key.indexOf(`${field}.`) === 0) {
        newSchema[key] = this._schema[key];
      }
    }
  }

  return schema._copyWithSchema(newSchema);
}

And call it like:

const newSchema = pickInNewOrder(schema, 'field3', 'field1')