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What Are Scalar Types In GraphQL?
originally posted on StepZen
You see scalar types everywhere you look in GraphQL. Take this type definition for example:
type Tracking {
origin: String!
destination: String
weight_lbs: Int
}Here,
String and Int are two of GraphQL's built-in scalar types. We'll talk about what that means and how you can add your own scalars to your GraphQL schemas.Here's how GraphQL.org defines scalar types:
A GraphQL object type has a name and fields, but at some point those fields have to resolve to some concrete data. That's where the scalar types come in: they represent the leaves of the query.
So, assuming that we are familiar with GraphQL queries, what are these leaves? In Graph Theory, we can structure our query in terms of a graph. Let's look at a graph for the query we defined above:
The nodes of the
Breed query tree are its leaves. That is, they are nodes with vertex degree 1. Vertex degrees are the number of edges (in this illustration, the arrows) connected to a vertex. These leaves will resolve to a scalar type, which can be one of GraphQL's built in scalar types or a custom type defined in the schema.GraphQL has its own set of scalar types that you don't have to initiate.
But what if you want to use a scalar that's not on the list, like
DateTime, you can create your own scalar type-- or, just use one of StepZen's if it fits your needs.StepZen 'builds in'
Date, DateTime & JSON scalar types so you can use them without having to implement your own (goodbye, extensive resolver logic!).So, using a
DateTime scalar in a StepZen GraphQL API is as simple as adding it to your schema:type Tracking {
origin: String!
destination: String
weight_lbs: Int
dateDelivered: DateTime
}So a query like:
query MyQuery {
deliveryByOrigin(origin: "London") {
destination
origin
weight_lbs
dateDelivered
}returns your data for
dateDelivered:"data": {
"deliveryByOrigin": {
"destination": "Cairo",
"origin": "London",
"weight_lbs": 12,
"dateDelivered": "02-10-2020"
}If you'd like to learn more about GraphQL and/or StepZen, head on over to our blog for a deep dive, or take a look at our docs.
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