Render empty array item fields when minItems is specified

[n1k0]

When minItems is specified for an array field, we should initialize the form with as many empty fields as the number specified.

[glasserc]

This is closed by #484.

[n1k0]

Released in v0.44.0.

[dropdevcoding]

I recently upgraded from 0.43.0 to 0.45.0 and it seems that this change causes unexpected behaviour in my application:

I have defined an array with minItems: 1 but this array is NOT marked as required. This will cause validation errors when submitting again without changing anything, since the changed default behaviour produces invalid state.

Could you please add an additional check respecting the required property before applying the newly introduced default behaviour?

[n1k0]

In my own understanding of the JSON schema spec, required and minItems are not interdependent. You can have this schema:

{
  type: "object",
  properties: {
    foo: {
      type: "array",
      items: {type: "number"},
      minItems: 1
    }
  }
}

And both {} and {foo: [42]} would be valid payloads against that schema, while {foo: []} would not.

Edit: Oh I see what you mean, {foo: []} currently passes validation. That's a bug indeed. Could you please create a separate issue for tracking this? Thanks.

Edit2: I was using minLength in my example, while minItems should be used. Validation works as expected, so I still don't understand what is the exact problem you're referring to.

[spacebaboon]

I'm having a problem with this change too. We're using an array with "ui:widget": "checkboxes" to render a checkbox group in a form, and minItems=1 to validate that the user has selected at least one.

It can be seen easily in the playground, under Arrays. Add "minItems": 1 to the multipleChoicesList section, and then delete the entry for multipleChoicesList in the formData section. When a form is first rendered, we have no formData, so this is the initial state, not an empty array.

Now click one of the checkboxes in the live demo and see what happens to the formData. A null entry is added after the selected values. Make it "minItems": 2 and 2 null entries are added. This also means that the minimum items validation does not work.

I thought that I could set a default for the field, by adding default: [] in the schema, but this changes the nulls to empty arrays.

It seems like minItems is serving two different purposes here. And perhaps default too. Perhaps default inside items could define the item default, and default outside could be the default for the array itself?

So my only option, unless I'm missing something, is to programmatically initialise the formData to be an empty array where I find an array type in the schema.

[spacebaboon]

I think I'll post my comment above as a new issue, it looks like a bug to me, and this issue has already been closed.

[Edit: This is now posted as #534.]