Keystone: Limit (filter) Relationship to a sub-set of List items

[mikehazell]

In K4 it was possible to define a filter on a Relationship field type. This allowed restricting relationships created through the admin ui to a subset of a List.

Related to: #376, #352

Example use cases

1) A Post has a relationship field for the assigned reviewer. Only User's with isAdmin === true can be assigned.

In K4 this was defined on the List as follows:

reviewer: {
    type: Relationship,
    ref: 'User',
    filters: { isAdmin: true },
},

2) A Site can have featuredTags. Those Tags must be related to the current site. ie:

featuredTags: {
    type: Relationship,
    ref: 'Tag',
    many: true,
    filters: { site: ':_id' },
},

[jesstelford]

This could be possible when we expose the hooks:

keystone.createList('Post', {
  fields: {
    reviewer: {
      type: Relationship,
      ref: 'User',
      hooks: {
        preUpdate: (data, item, context) => {
          if (!data.isAdmin) throw new Error('Not allowed');
        }
      }
    }
  }
});

[mikehazell]

Yes that's one side of it. The other side is that in the Admin UI you are not presented with invalid options when creating the relationship.

[stale[bot]]

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[MadeByMike]

The view section should now be done as a custom view. This use-case becomes rather simple if we land: https://github.com/keystonejs/keystone/pull/2885