Is it possible to filter a collection based on a collection field on the content type in graphql & contentful

This might be impossible in graphql/contentful or introduce too much complexity but I'm trying to query a collection and filter on a collection field, something like the following...

query {
  eventCollection(
    where: {
      OR: [
        { categoryCollection: { key: "fashion" } }
      ]
    }
  ) {
  items {
    slug
  }
}

My back up plan is to query all the events and filter in the client but I thought it would be possible to do the above.

Contentful DevRel here. 👋

Currently, that's not possible. But what you can do is flip the query around and filter on the categoryCollection and then use linkedFrom to request the items linking to it.

query {
  categoryCollection(where: {
    key: "fashion
  }) {
    items {
      title
      linkedFrom {
        eventCollection {
          items {
            slug
          }
        }
      }
    }
  }
}