GraphQL technology in a brief with examples in Elixir programming language, and with a small comparison with REST model.

1. GraphQL – the future
of APIs?
- OR -
GraphQL in a brief
Dmitry Stropalov, Sizmek Kraków 2017

2. What is GraphQL
• GraphQL is a (query) language
- declarative
- hierarchical
- strongly typed
• GraphQL is a runtime
- execution layer
- technology agnostic
2

3. Yet another technology?
• Era of mobile devices
• Flexibility & Transparency
• Productivity & Costs
3

4. Some example
4

5. I have a data. What’s next?
5
1. Define a schema for data representation
GraphQL Schema:
type Campaign {
name: ID!
title: String
running: Boolean
ads: [Ad]
}
Elixir DSL:
object :campaign do
field :id, non_null(:id)
field :title, :string
field :running, :boolean
field :ads, list_of(:ad),
resolve: assoc(:ads)
end

6. I have a data. What’s next?
6
2. Define a schema of queries and mutations
GraphQL Schema:
type Query {
campaign(id: ID!): Campaign
}
Elixir DSL:
field :campaign, :campaign do
arg :id, non_null(:id)
resolve &CampaignResolver.find/2
end

7. I have a data. What’s next?
7
3. Implement resolvers for queries and mutations
Elixir:
def find(%{id: id}, _info) do
case Repo.get(Campaign, id) do
nil -> {:error, "Campaign #{id} not found"}
campaign -> {:ok, campaign}
end
end

8. I have a data. What’s next?
8
4. Make some queries
GraphQL query:
query {
campaign(id: 1) {
running
ads {
budget {
amount
}
}
}
}
GraphQL mutation:
mutation {
createCampaign(
title: "New campaign",
running: false, ads: [
{title: “LI 1"}
]) {
id
}
}

9. GraphQL Schema
9
• Scalar Types
• Lists & Enumeration Types
• Object Types
• Interfaces & Unions
• Arguments
• Input types

10. Scalar Types
10
• Int: A signed 32‐bit integer.
• Float: A signed double-precision floating-point value.
• String: A UTF‐8 character sequence.
• Boolean: true or false.
• ID: non human-readable String.
• Custom scalars via scalar keyword.

11. Lists & Enumeration Types
• Lists defined with [ and ] around type.
• Enum – special type of scalar with a restricted set of
possible values:
enum Episode {
FIRST
SECOND
THIRD
}
11

12. Object Types
• Object type – named set of fields with theirs types.
• Fields could be scalars or other object types, enums, lists.
• Fields could be marked as non-nullable:
type Ad {
title: String!
targetings: [Targeting!]!
}
12

13. Interfaces & Unions
• Interface – an abstract object type:
interface Player {
nickname: String!
}
type User implements Player {
nickname: String!
…
}
• Union – specifies a set of possible object types:
union SearchResult = Picture | Video | Document
search(text: "Kraków") {
… on Picture { size }
… on Video { length }
… on Document { format }
}
13

14. Arguments
• Every field of an object type can have zero or more
arguments:
type FuelTank {
volume(unit: VolumeUnit = LITRE): Float
}
• All arguments are named.
• Could be required or optional.
14

15. Input Types
• Input types – object types used for mutations.
• Input and output object types can’t be mixed.
• No arguments on input object fields.
15

16. GraphQL Queries
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Fields, aliases, fragments and other things

17. Introspection & Docs
• Introspection is built-in via special __schema object.
• Any type introspection via __type object.
• Documentation is a part of schema definition:
@desc "Get campaign by ID."
field :campaign, :campaign do
arg :id, non_null(:id), description: "Specifies campaign ID.”
resolve &CampaignResolver.find/2
end
17

18. API Versioning
• GraphQL can’t have “v1”-style versioning.
• Evolution is the key.
18

19. One more “v1” thing
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20. –Monty Python
“And now for something completely different …”
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21. The Glory of REST
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From the article “Richardson Maturity Model” by M.Fowler

22. GraphQL & REST
• GraphQL is a language, specification and tools while REST is an
architectural concept.
• GraphQL is completely independent of a transport protocol used.
• With GraphQL you can think in terms of a business logic objects
instead of resources.
• Different caching approaches.
• API payload optimisations.
• Field usage monitoring.
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23. Adoption
• Facebook
• GitHub
• Twitter
• Airbnb
• The New York Times
• Wirtualna Polska
• Coursera
• Dailymotion
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24. The End