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= MicroProfile GraphQL
:description: Helidon GraphQL MicroProfile
:keywords: helidon, graphql, microprofile, micro-profile
:feature-name: MicroProfile GraphQL
:rootdir: {docdir}/..
:microprofile-bundle: false
include::{rootdir}/includes/mp.adoc[]
== Contents
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== Overview
Helidon MP implements the
link:{microprofile-graphql-spec-url}[MicroProfile GraphQL specification].
This specifcation describes how applications can be built to expose an endpoint for GraphQL.
GraphQL is an open-source data query and manipulation language for APIs,
and a runtime for fulfilling data queries.
It provides an alternative to, though not necessarily a replacement for, REST.
include::{rootdir}/includes/dependencies.adoc[]
[source,xml]
----
io.helidon.microprofile.graphql
helidon-microprofile-graphql-server
----
== API
The MicroProfile GraphQL specification defines a number of key annotations to be used when writing a GraphQL endpoint:
* `@GraphQLApi` - identifies a CDI Bean as a GraphQL endpoint
* `@Query` - identifies a method as returning one or more entities
* `@Mutation` - identifies a method which creates, deletes or updates entities
For example, the following defines a GraphQL endpoint with a number of queries and mutations that work
against a fictional `CustomerService` service and `Customer` class.
[source,java]
.Simple ContactGraphQLApi
----
include::{sourcedir}/mp/GraphqlSnippets.java[tag=snippet_1, indent=0]
----
<1> a query with no-arguments that will return all `Customer` s
<2> a query that takes an argument to return a specific `Customer`
<3> a query that optionally takes a name and returns a collection of `Customer` s
<4> a mutation that creates a Customer and returns the newly created `Customer`
The example above would generate a GraphQL schema as shown below:
[source,graphql]
.Sample GraphQL schema
----
type Query {
findAllCustomers: [Customer]
findCustomer(customerId: Int!): Customer
findCustomersByName(name: String): [Customers]
}
type Mutation {
createCustomer(customerId: Int!, name: String!, balance: Float!): Customer
}
type Customer {
id: Int!
name: String!
balance: Float
}
----
After application startup, a GraphQL schema will be generated from your annotated API classes
and POJO's and you will be able to access these via the URLs described below.
=== Building your application
As part of building your application, you must create a Jandex index
using the `jandex-maven-plugin` for all API and POJO classes.
[source,xml]
.Generate Jandex index
----
io.smallrye
jandex-maven-plugin
make-index
----
NOTE: As per the instructions xref:introduction/microprofile.adoc[here] ensure you have added a
`src/main/resources/META-INF/beans.xml` file, so the CDI implementation can pick up your classes.
=== Accessing the GraphQL endpoints
After starting your application you should see a log message indicating that GraphQL
is in the list of features. You can access the GraphQL endpoint at `http://host:port/graphql`, and
the corresponding schema at `http://host:port/graphql/schema.graphql`. See <> for
additional information on how to change the location of these resources.
If you wish to use the
link:https://github.com/graphql/graphiql[GraphQL UI] then please see the
link:{helidon-github-examples-url}/microprofile/graphql[GraphQL MP Example].
== Configuration
The specification defines the following configuration options:
[cols="2,2,5"]
|===
|key |default value |description
|`mp.graphql.defaultErrorMessage` |`Server Error` |Error message to send to caller in case of error
|`mp.graphql.exceptionsBlackList` |{nbsp} |Array of checked exception classes that should return default error message
|`mp.graphql.exceptionsWhiteList` |{nbsp} |Array of unchecked exception classes that should return message to caller (instead of default error message)
|===
include::{rootdir}/includes/graphql.adoc[]
== Examples
For a complete example, see
link:{helidon-github-examples-url}/microprofile/graphql[GraphQL MP Example].
== Additional Information
* link:http://graphql.org[GraphQL].
== Reference
* link:{microprofile-graphql-javadoc-url}[MicroProfile GraphQL Javadocs].