Unions

Unions allow you to compose multiple types together. Let's say we have a search query that can either return a post or user. We can define a Union type like below to allow this.

union SearchResult = Post | User

To define the Union in Groot, we need to create a new struct that embeds groot.BaseType and all the members of the Union.

type SearchResult struct {    groot.UnionType    Post    User}

You can then use the type anywhere you like.

type Query struct {    Search SearchResult `json:"search"`}
type SearchArgs struct {    Query string `json:"query"`}
type (q Query) ResolveSearch(args SearchArgs) (SearchResult, error) {    searchResults, err := db.Search(args.Query)
    results := []SearchResult{}    for _, result := range searchResults {        switch result := result.(type) {        case Post:            results = append(results, SearchResult{Post: result})        case User:            results = append(results, SearchResult{User: result})        }    }
    return results, nil}

If you're coming from another GraphQL implementation, you would notice there's no type resolver here to determine which type the union is returning. In Groot, you don't need to define it manually since the type resolution is done when you initialize the value, i.e. the type which we have to return will have a non zero value, and all others will have a zero value. For example, if we have SearchResult{Post: result}, SearchResult.Post has a non zero value while all other field have a zero value, which means we can resolve the type to Post.