[graphql] Allow filtering children of node too

[mathieucaroff]

Summary

Currently, in Gatsby's GraphQL, it is possible to filter children nodes of top-level "all-instances-of-a-type" fileds like "allFile", "allSite", "allPlugin", etc.

For instance, this works:

query {
  allFile (filter: { name: {eq: "defaultIcon") {
    childImageSharp {
      fluid {
        ...GatsbyImageSharpFluid
        src
      }
    }
  }
}

What is not possible to do, that should be, is filtering children nodes of other nodes.

Basic example

The below GraphQl request uses filter on childrenFile. This is not currently possible, in gatsby@2.4.6.

query {
  allGithubRepo {
    nodes {
      repo
      childrenFile (filter: { name: {eq: "defaultIcon") {
        childImageSharp {
          fluid {
            ...GatsbyImageSharpFluid
            src
          }
        }
      }
  }
}

According to @pieh, this feature would have to be implemented inside gatsby core.

Motivation

(M1)
It is a bit confusing that filtering is available on on top-level "all-instances of type" fields, but not on node children. This lead to issue #8764 being raised.

(M2)
On the project I'm working on, I use createRemoteFileNode from gatsby-source-filesystem to obtain images from github repositories, to use them in pages. The images can the default icon, some other icon, or a screenshot. All are children of the repository, but they'll be used in different component. On of the ideas behind GraphQL is that the response to a query should contain no more than the needed data. This is not possible without filtering

(M3) #8764 (comment) (@RIP21)

@pieh What about to add support for such filtering? Imagine you have 300 different keys under, and all of that will be fetched and added as a JSON making build of 10k pages weights around 10GB.
Or maybe any idea how to add such thing to it ourself, like a fork.

[freiksenet]

Hi! That's a good idea. If you want to make a PR, here are some pointers.

Children/child fields are added in this function

Filter parameters are created in [this function)(https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/schema/schema.js#L476).

Filter types are cached, so you can safely call getFilterTC again in the addConvenienceChildrenFields function too. You can use that then to add filter parameter to it.

[emckay]

+1 for this before it goes stale.

I can work around this for now by doing the children filtering when I create the page in gatsby-node and passing the filtered results to the page via context, but it feels like a bit of a hack. It'd be nice to be able to do the filtering in graphql in the page query instead.

[antonioperic]

+1 for this

[loganwishartcraig]

Another +1!

[thekevinbrown]

We could really use this too.

[LekoArts]

Please refrain from adding "+1" comments, GitHub has the reaction feature for that. Thanks!

If you want to contribute to this, please read our documentation here: https://www.gatsbyjs.org/contributing/how-to-contribute/

[martin-braun]

Please add this together with limit and skip on children. Also I think the sort should be available on children, separately, so I can configure sort for every level, instead of only for one field in all levels.

Is there any update regarding this?

[byronlanehill]

Just wondering if there is any update on this? I am building a custom source plugin that requires this functionality.