API v1 with GraphQL

[barrettj12]

Create a v1 of the chords API using GraphQL.

The new API schema lives in api.graphql. The server-side code is generated using gqlgen.

TODO

• [x] write a draft schema
• [x] generate server code using gqlgen
• [x] fill in the resolvers at gqlgen/api.resolvers.go
• [ ] play around with some manual GraphQL queries
• [ ] iterate on the schema
• [ ] generate Go client for the CLI
• [ ] generate JS client for the front-end
  • I think this should work?

[barrettj12]

This change probably necessitates a new data model too, since artists/albums are now their own entities, rather than something derived from songs.

[barrettj12]

This explains how to do custom resolvers for a type: https://gqlgen.com/getting-started/

[barrettj12]

Some more thoughts:

• In the data model, it makes sense to store the "object type" fields by ID, rather than as the entire object. For example:

  type Artist struct {
    ID             ArtistID   `json:"id"`
    Name           string     `json:"name"`
    Albums         []AlbumID  `json:"albums"`
    RelatedArtists []ArtistID `json:"relatedArtists"`
  }

  This necessitates separating the data model representation from the GraphQL API representation:

  type Artist struct {
    ID             string    `json:"id"`
    Name           string    `json:"name"`
    Albums         []*Album  `json:"albums"`
    RelatedArtists []*Artist `json:"relatedArtists"`
  }

  The GraphQL resolvers are responsible for "resolving" an ID into the corresponding object.

• To keep the DB interface small, perhaps we should just have a single method for each data type, which takes a struct of parameters that can be used to filter the returned objects. For example:

  type ChordsDBv1 interface {
    Artists(ArtistsFilters) []Artist
    Albums(AlbumsFilters) []Album
    Songs(SongsFilters) []Song
  }

  where ArtistFilters contains all the possible ways we might want to filter artists, e.g.

  type ArtistFilters struct {
    id        ArtistID
    name      string
    album     AlbumID
    relatedTo ArtistID
    song      SongID
  }

[barrettj12]

We now have a fully functional GraphQL API (for queries / GET requests only). Let's wire this up to the real server, then I think this is a good spot to merge.

Next logical steps are:

• defining the new data model and migrating over
• defining and implementing mutations