Add @appendNode and @prependNode directives for updating the store

[zth]

This adds two new directives, @appendNode and @prependNode, for updating the store declaratively. The directives will create an edge for the annotated object and prepend/append that edge to the provided connections. It works with single nodes as well as lists of nodes.

Example:

mutation AddComments(
  $input: AddCommentsInput!, 
  $connections: [String!]!, 
  $edgeTypeName: String!
) {
  addComments(input: $input) {
    # It works for lists of nodes as well as for single nodes
    comments @appendNode(connections: $connections, edgeTypeName: $edgeTypeName) {
      id
    }

    # This mutation naturally doesn't make sense, but is just here to illustrate that this works for a single node as well
    comment @appendNode(connections: $connections, edgeTypeName: $edgeTypeName) {
      id
    }
  }
}

[josephsavona]

cc @kassens @tyao1

[tyao1]

Looks great.
Does it work if the edgeType is a constant in the directive?

[zth]

@tyao1 Thanks for having a look. Yes it does. I added a test to show it, please see the latest commit.

[tyao1]

Awesome! Thanks for the extra tests!

[facebook-github-bot]

@tyao1 has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@tyao1 merged this pull request in 0fe732d.

[anatooly]

ERROR:
Variable '$connections' was defined as type '[String!]!' but used in a location expecting the type '[ID!]!'

[tobias-tengler]

Would be great if these directives could be documented!

[anatooly]

How do this variant?

mutation CommentCreateMutation(
  $connections: [String!]!
  $input: CommentCreateInput
) {
  commentCreate(input: $input) @appendNode(
      connections: $connections
      edgeTypeName: "CommentEdge"
    ) {
      id
      ...Comment_comment
    }
  }
}

index.js:1 Warning: MutationHandlers: Expected target node to exist.

[giautm]

Hey @anatooly , I found if I use directives on a field with arguments they will not work. Please retry with a field without agrument, I believe there is a bug in implement of those directives