Automatic support for many-to-many fields through linked node creation in source plugins

[flmuel]

So in the last few days I tried to get only Wordpress posts with a passed variable (id of a category)...
I am creating category sites in gatsby-node, which uses my category template.

Is there a simple way in GraphQL to filter after categories with this plugin?
Categories is the only node which is not selectable in the GraphiQL Editor...

{
  allWordpressPost(filter: {categories is not here}) {
    edges {
      node {
        id
        categories {
          id
        }
      }
    }
  }
}

[calcsam]

This is a limitation of how you can query many-to-many fields in GraphQL with Gatsby -- we don't automatically create two-way Connection links between nodes pulled in by some plugins, which is required to do the type of querying you discuss.

This would be a bit of a complicated PR and should happen in gatsby core rather than the Wordpress source plugin; feel free to dive in if you'd like.

https://github.com/gatsbyjs/gatsby/blob/57f7b0d372a7461f019ce86a9003371d45204f3b/packages/gatsby/src/schema/build-node-connections.js

[flmuel]

Thank you for your answer! This drove me crazy... Well, this core file you linked needs time for understanding, at least for me :D Maybe I will look into this later.

[loremipson]

This is a pretty big limitation that we just ran into as well. Just being a second voice for now.

[KyleAMathews]

Would love to help someone through a PR to add support for filtering on linked nodes 👍

[alvinthen]

I'd love to help on supporting filtering on linked nodes, would be great to point me to where to start in Gatsby, I can work my way on GraphQL

[KyleAMathews]

@alvinthen sweet! That'd be a huge help.

The two files you'll be working in are:

• https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/schema/infer-graphql-input-fields.js
• https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby/src/schema/__tests__/infer-graphql-input-type-test.js

This line in particular is where the action should happen

gatsby/packages/gatsby/src/schema/infer-graphql-input-fields.js

Line 204 in c0c4bb7

// Input arguments on linked fields aren't currently supported

Adding support for ___NODE style links is step 1 as it's the most common way of linking. There are two other main ones — links to files are automatically created as well + people can manually create links in their gatsby-config.js. An initial PR could focus just on supporting ___NODE however.

[KyleAMathews]

@alvinthen fixed this! Thanks!

[flmuel]

@KyleAMathews reopen?