Query Fragments

GraphQL Fragments, as the name implies, are pieces of a query. They mostly serve two purposes:

  • Executing part of a query conditionally - only when the result is of a specified type. In the example above fieldSubtitle will be evaluated only when the node with id 1 is an Article. If it turns out to be a Basic Page, the fragment will be omitted and the response will just be one field shorter without raising any exceptions.

  • Reusability. A fragment can be given a name and be used more than once.

Lets look at the following query :

{
nodeById(id: "1", language: en) {
... on NodeArticle {
fieldCategory {
entity {
...termFragment
}
}
fieldTags {
entity {
...termFragment
}
}
}
}
}
‚Äč
fragment termFragment on TaxonomyTerm {
name
tid
}

There are two fragments in this query. The first one starting on line 3 is an inline fragment. We need it because fieldCategory and fieldTags are only attached to Articles and nodeById can return any node. The other one, defined on line 18, is a named fragment thanks to which we don't need to repeat the sub-queries for fieldCategory and fieldTags.

You can take advantage of fragments to make very complex easier to understand by breaking them down into smaller pieces, they are also a very good way to share common things like we see above the termFragment, make the code cleaner and easier to refactor.