This PR adds an ability to specify a virtual field in this way
```js
{
slug: 'posts',
fields: [
{
name: 'title',
type: 'text',
required: true,
},
],
},
{
slug: 'virtual-relations',
fields: [
{
name: 'postTitle',
type: 'text',
virtual: 'post.title',
},
{
name: 'post',
type: 'relationship',
relationTo: 'posts',
},
],
},
```
Then, every time you query `virtual-relations`, `postTitle` will be
automatically populated (even if using `depth: 0`) on the db level. This
field also, unlike `virtual: true` is available for querying / sorting /
`useAsTitle`.
Also, the field can be deeply nested to 2 or more relationships, for
example:
```
{
name: 'postCategoryTitle',
type: 'text',
virtual: 'post.category.title',
},
```
Where the current collection has `post` - a relationship to `posts`, the
collection `posts` has `category` that's a relationship to `categories`
and finally `categories` has `title`.
1c99f46e4f