Feature/define sorting

[bjoerge]

This adds support for defining a set of sort options on schema types:

Example:

{
  type: 'object',
  name: 'myType',
  // ...
  sorting: [
    {
      title: 'Title',
      name: 'title',
      orderBy: {
        title: 'asc',
        publicationYear: 'asc'
      }
    }
  ]
  //...
}

These will be options for sorting the list of documents, together with _createdAt and _updatedAt

This also introduces a second argument to preview.prepare called viewOptions. If the document to be previewed is subject to a certain sort order, the sorting will be passed in on viewOptions.sorting. This allows for returning another preview title if the list of documents should be sorted by a field that is not normally visible, e.g. a localized field.

[rexxars]

Looks solid! A few nitpicks, but otherwise 👍

[rexxars]

Sorry for derailing, but should I have added hidden to this list, too?

[bjoerge]

Yeah! Looks like readOnly is missing there too.

[rexxars]

It's not clear to me why these are double-underscored - is this intentional? If so, maybe add a comment explaining why?

[bjoerge]

You are right - The double underscores were there to prevent conflicts with possible user-defined sort options with the same name. But on second thought; being able to override the semantics of updatedAt is actually a nice feature that we could document.

[rexxars]

Perhaps we should allow icon to be specified in sort options? It would make sense to allow say a clock/calendar icon for date sorting and a Aa↓ icon for sorting by title, for instance.

[bjoerge]

Totally! Will fix.

[thomax]

This looks like a solid implementation of a sorely needed feature. Thumbs up!

[bjoerge]

After a few IRL discussions we'd like to do a few minor changes to the proposed format:

• Change the key from sorting to orderings
• Change from orderBy on each ordering to by.
• Change the format of by from an object to an array with field + direction

Updated format:

{
  type: 'object',
  name: 'myType',
  // ...
  orderings: [
    {
      title: 'Title',
      name: 'title',
      by: [
        {field: 'title', direction: 'asc'},
        {field: 'publicationYear', direction: 'desc'}
      ]
    }
  ]
  //...
}