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https://github.com/google/rejoiner

Generates a unified GraphQL schema from gRPC microservices and other Protobuf sources
https://github.com/google/rejoiner

graphql graphql-server grpc protobuf

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Generates a unified GraphQL schema from gRPC microservices and other Protobuf sources

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README 

        
# Rejoiner



[![Build Status](https://travis-ci.org/google/rejoiner.svg?branch=master)](https://travis-ci.org/google/rejoiner)

[![Coverage Status](https://coveralls.io/repos/github/google/rejoiner/badge.svg?branch=master)](https://coveralls.io/github/google/rejoiner?branch=master)



[![Maven Central](https://maven-badges.herokuapp.com/maven-central/com.google.api.graphql/rejoiner/badge.svg)](http://mvnrepository.com/artifact/com.google.api.graphql/rejoiner/0.0.4)



 - Creates a uniform GraphQL schema from microservices

 - Allows the GraphQL schema to be flexibly defined and composed as shared components

 - Generates GraphQL types from Proto definitions

 - Populates request Proto based on GraphQL query parameters

 - Supplies a DSL to modify the generated schema

 - Joins data sources by annotating methods that fetch data

 - Creates Proto [FieldMasks](https://developers.google.com/protocol-buffers/docs/reference/java/com/google/protobuf/FieldMask) based on GraphQL selectors



 ![Rejoiner Overview](./website/static/rejoiner_overview.svg)



## Experimental Features



These features are actively being developed.



 - Expose any GraphQL schema as a gRPC service.

 - Lossless end to end proto scalar types when using gRPC.

 - Relay support [[Example](examples-gradle/src/main/java/com/google/api/graphql/examples/library)]

 - GraphQL Stream (based on gRPC streaming) [[Example](examples-gradle/src/main/java/com/google/api/graphql/examples/streaming)]



## Schema Module



SchemaModule is a Guice module that is used to generate parts of a GraphQL

schema. It finds methods and fields that have Rejoiner annotations when it's

instantiated. It then looks at the parameters and return type of these methods

in order to generate the appropriate GraphQL schema. Examples of queries,

mutations, and schema modifications are presented below.



## GraphQL Query



```java

final class TodoQuerySchemaModule extends SchemaModule {

  @Query("listTodo")

  ListenableFuture listTodo(ListTodoRequest request, TodoClient todoClient) {

    return todoClient.listTodo(request);

  }

}

```



In this example `request` is of type `ListTodoRequest` (a protobuf message), so

it's used as a parameter in the generated GraphQL query. `todoService` isn't a

protobuf message, so it's provided by the Guice injector.



This is useful for providing rpc services or database access objects for

fetching data. Authentication data can also be provided here.



Common implementations for these annotated methods:

 - Make gRPC calls to microservices which can be implemented in any language

 - Load protobuf messages directly from storage

 - Perform arbitrary logic to produce the result



## GraphQL Mutation



```java

final class TodoMutationSchemaModule extends SchemaModule {

  @Mutation("createTodo")

  ListenableFuture createTodo(

      CreateTodoRequest request, TodoService todoService, @AuthenticatedUser String email) {

    return todoService.createTodo(request, email);

  }

}

```



## Adding edges between GraphQL types



In this example we are adding a reference to the User type on the Todo type.

```java

final class TodoToUserSchemaModule extends SchemaModule {

  @SchemaModification(addField = "creator", onType = Todo.class)

  ListenableFuture todoCreatorToUser(UserService userService, Todo todo) {

    return userService.getUserByEmail(todo.getCreatorEmail());

  }

}

```

In this case the Todo parameter is the parent object which can be referenced to

get the creator's email.



This is how types are joined within and across APIs.



![Rejoiner API Joining](./website/static/rejoiner.svg)



## Removing a field



```java

final class TodoModificationsSchemaModule extends SchemaModule {

  @SchemaModification

  TypeModification removePrivateTodoData =

      Type.find(Todo.getDescriptor()).removeField("privateTodoData");

}

```



## Building the GraphQL schema

```java

import com.google.api.graphql.rejoiner.SchemaProviderModule;



public final class TodoModule extends AbstractModule {

  @Override

  protected void configure() {

    // Guice module that provides the generated GraphQLSchema instance

    install(new SchemaProviderModule());



    // Install schema modules

    install(new TodoQuerySchemaModule());

    install(new TodoMutationSchemaModule());

    install(new TodoModificationsSchemaModule());

    install(new TodoToUserSchemaModule());

  }

}

```



## Getting started



### Dependency information



Apache Maven

```xml



    com.google.api.graphql

    rejoiner

    0.0.4



```



Gradle/Grails

`compile 'com.google.api.graphql:rejoiner:0.0.4'`



Scala SBT

`libraryDependencies += "com.google.api.graphql" % "rejoiner" % "0.0.4"`



## Supported return types



All generated proto messages extend `Message`.

 - Any subclass of `Message`

 - `ImmutableList extends Message>`

 - `ListenableFuture extends Message>`

 - `ListenableFuture>`



## Project information



 - Rejoiner is built on top of [GraphQL-Java](https://github.com/graphql-java/graphql-java) which provides the core

   GraphQL capabilities such as query parsing, validation, and execution.  

 - Java code is formatted using [google-java-format](https://github.com/google/google-java-format).

 - Note: This is not an official Google product.