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Spring Framework GraphQL Library

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Intro

Initially project was inspired by multiple projects

and main idea was transformed into generic lightweight mechanism for schema definition in java. It will be helpful for those who starts coding schema from scratch or upgrading technology stack moving to GraphQL.

The library facilitates GraphQL schema development in SpringFramework environment heavily using annotations. The entire schema lives in Spring context which means developer can leverage all Spring features like AOP, IO etc. There is one important dependency on graphql-java for schema imperative building and GraphQL query execution. The query execution strategy for the READ and MUTATE queries is based on Reactor Reactive Streams with high level of parallelism.

Note: process has been started on moving to complete Reactor RS Stack leveraging Netty GraphQL NIO server (spring boot starters should be updated as well). Reactor execution strategy will be strategic one available in the future releases. RxJava-based strategies are deprecated and won't be maintained anymore.

graphql-spring-boot-starter and graphiql-spring-boot-starter are available in graphql-spring-boot repository.

Requires

some of the dependencies can be removed in the future.

repositories {
    // stable build
    jcenter()
    // development build
    maven { url  "http://dl.bintray.com/oembedler/maven" }
}

Dependency:

dependencies {
  compile 'com.embedler.moon.graphql:spring-graphql-common:INSERT_LATEST_VERSION_HERE'
}

How to use the latest build with Maven:

<repository>
    <snapshots>
        <enabled>false</enabled>
    </snapshots>
    <id>bintray-oembedler-maven</id>
    <name>bintray</name>
    <url>http://dl.bintray.com/oembedler/maven</url>
</repository>

Dependency:

<dependency>
    <groupId>com.embedler.moon.graphql</groupId>
    <artifactId>spring-graphql-common</artifactId>
    <version>LATEST_VERSION_HERE</version>
</dependency>

Usage

The entire schema definition is annotations driven. There is a good support for generic types - so don't miss chance to use them if it's appropriate (see Relay Support as an example). Class level annotations (like @GraphQLSchema, @GraphQLObject etc) are Spring @Component annotations.

@GraphQLSchema
public class TodoSchema {

    @GraphQLSchemaQuery
    private RootObjectType root;

    public static class AddTodoIn {
        private String text;
    }
    
    // default value provider for an input mutation parameter 
    public AddTodoIn getAddTodoInputDefaultValue() {
        AddTodoIn addTodoInput = new AddTodoIn();
        addTodoInput.setText("--- default text ---");
        return addTodoInput;
    }

    @GraphQLMutation
    public
    @GraphQLOut("todoEdge")
    TodoObjectType.TodoEdgeObjectType addTodoMutation(@GraphQLIn("addTodoInput", defaultProvider = "getAddTodoInputDefaultValue") AddTodoIn addTodoInput) {
    
        // mutation implementaion goes here
        
        return todoEdgeObjectType;
    }

Use @GraphQLSchemaQuery to set root query for the schema.

Supported types

All Java wrapper types directly map to GraphQL types:

same for corresponding Java primitives. Long, Float types are passed in the GraphQL queries as a Strings. It's due to underlying query parser implementation.

Extensions:

Double, Date and Timestamp values are passed in the GraphQL queries as a String values.

Creating a new Object Type

@GraphQLObject annotation is used to mark class as GraphQLObjectType. Recursive object type references are handled automatically.

@GraphQLObject("Root")
public class RootObjectType {

    @GraphQLNonNull
    @GraphQLDescription("Root query version number")
    private String version;

    @GraphQLField
    @GraphQLDescription("Root viwer node as per Relay spec")
    public UserObjectType viewer(/** no input expected **/) {
    
        // custom data fetcher for the field with name 'viewer'
        
        return userObjectType;
    }
}

If class field is accessible through getters \ setters - define field as a class member. All class fields are included into object definition unless @GraphQLIgnore annotation is used. If field needs custom data fetcher - define field as a class method and mark class with @GraphQLField annotation. @GraphQLDescription annotation can be used in most likely any context to set description for the GraphQL schema element.

Creating a new Interface Type

If interface must be considered as a part of the object hierarchy use GraphQLInterface annotation. Interfaces not marked with the annotation are ignored.

@GraphQLInterface("Node")
public interface RelayNode {

    @GraphQLID("id")
    @GraphQLNonNull
    @GraphQLDescription("GraphQL Relay global object unique identifier")
    String getId(RelayNode relayNode);
}

Creating a new Enum Type

Java enums are automatically discovered and mapped to GraphQLEnumType.

    // annotation is not required if enum names are acceptable as values
    @GraphQLEnum(valueProvider = "getValue")
    public enum Episode {
        @GraphQLDescription("Released in 1977.")
        NEWHOPE,
        @GraphQLDescription("Released in 1980.")
        EMPIRE,
        @GraphQLDescription("Released in 1983.")
        JEDI;

        // enum field value provider must be static method with 1 input argument - its own enumeration type
        public static Object getValue(Episode self) {
            if (self == NEWHOPE)
                return 4;
            else if (self == EMPIRE)
                return 5;
            else
                return 6;
        }
    }

@GraphQLEnum is not required for enum defition as Java enums are discovered automatically by library. On the other side using that annotation enum name and value can be changed. Note optional valueProvider annotation element should point to static method in enum which accepts one single argument - enum itself and returns value for the enum. The return value can be of any desired type. Also default value for enum can be provided through SpEL expression as follows:

    // avaliable context objects are `obj` (enum instance itself) and `cls` - enum class
    @GraphQLEnum(defaultSpel = "#obj.getActualValue()")
    public enum EpisodeV2 {
        @GraphQLDescription("Released in 1977.")
        NEWHOPE(4),
        @GraphQLDescription("Released in 1980.")
        EMPIRE(5),
        @GraphQLDescription("Released in 1983.")
        JEDI(6);

        int actualValue;

        EpisodeV2(int val) {
            actualValue = val;
        }

        public int getActualValue() {
            return actualValue;
        }
    }

Creating a new Union Type

GraphQL Union type is a java interface marked with @GraphQLUnion annotation. While annotation value (type name) can be empty possibleType annotation field must contain list of possible types for union type.

    @GraphQLUnion(value = "Pet", possibleTypes = {Dog.class, Cat.class})
    public interface PetsUnionType {
       // empty marker
       // possible types must implement this interface
    }
    
    //...
    
    @GraphQLField("pets")
    public List<PetsUnionType> getPets() {
       List<PetsUnionType> pets = new ArrayList<>();
       pets.addAll(cats);
       pets.addAll(dogs);
       return pets;
    }

Creating a Object-Input Type

Input method arguments are automatically converted into GraphQLInputObjectType. All expected input arguments to either mutation or data fetcher have to be marked with @GraphQLIn annotation. Names for the method parameters can be automatically discovered using org.springframework.core.DefaultParameterNameDiscoverer. However it's recommended to define parameter name in @GraphQLIn annotation value field. To provide default value for an input parameter the defaultProvider annotation field should point to the local class method (either static or instance). The return value of the method must be of the same type (derived type) as defined in a mutation method signature.

    @GraphQLField
    public TodoObjectType.TodoConnectionObjectType todos(@GraphQLIn RelayConnectionArguments args) {
       
       // `args` is extracted from arguments context
       
    }

    @GraphQLField("manager")
    public UserObjectType getManager(@GraphQLIn UserObjectType employee) {
    
       // `employee` is extracted from upstream 'source' element as input parameters are empty
    
    }

Mutations

Mutation must be declared in the class marked as @GraphQLSchema annotation. Use @GraphQLMutation annotation to mark method as a GraphQL Mutation. Input method parameters are input variables. Method returned result is a mutation nested nodes.


    // default value provider for an input mutation parameter 
    public AddTodoIn getAddTodoInputDefaultValue() {
        AddTodoIn addTodoInput = new AddTodoIn();
        addTodoInput.setText("--- default text ---");
        return addTodoInput;
    }

    @GraphQLMutation("addTodoMutation")
    public
    @GraphQLOut("todoEdge")
    TodoObjectType.TodoEdgeObjectType addTodoMutation(@GraphQLIn("addTodoInput", defaultProvider = "getAddTodoInputDefaultValue") AddTodoIn addTodoInput, AddTodoIn2 addTodoInput2) {
    
        // `addTodoInput` created based on input `variables`
        // `addTodoInput2` is skipped as it's not marked explicitly as `@GraphQLIn` parameter
    
    }

Value for @GraphQLMutation is optional. If omitted - method name is used as a name of a mutation. @GraphQLOut is used to give a name for a mutation output type. All expected input variables have to be marked with @GraphQLIn annotation. To provide default value for an input parameter the defaultProvider annotation field should point to the local class method (either static or regular). The return value of the method must be of the same type (derived type) as defined in mutation method signature. Also default value can be provided using SpEL expression:

    @GraphQLField("manager")
    public UserObjectType getManager(UserObjectType employee,
                                     @GraphQLIn(value = "ids", defaultSpel = "T(java.util.Collections).EMPTY_SET") Set<String> ids) {
        // omitted for simplicity
    }

Spring configuration

    // there must be either `@ComponentScan` annotation defined for a schema base package 
    // or all beans must be instantiated explicitly in configuration class
    @Configuration
    @ComponentScan(basePackages = "com.oembedler.moon.graphql.test.todoschema")
    public static class TodoSchemaConfiguration {

        // use as is
        @Bean
        public GraphQLSchemaBeanFactory graphQLSchemaBeanFactory() {
            return new SpringGraphQLSchemaBeanFactory();
        }

        // configuration can be customized depending on the case
        @Bean
        public GraphQLSchemaConfig graphQLSchemaConfig() {
            GraphQLSchemaConfig graphQLSchemaConfig = new GraphQLSchemaConfig();
            return graphQLSchemaConfig;
        }

        // use as is
        @Bean
        public GraphQLSchemaBuilder graphQLSchemaBuilder() {
            return new GraphQLSchemaBuilder(graphQLSchemaConfig(), graphQLSchemaBeanFactory());
        }

        // use as is
        @Bean
        public GraphQLSchemaHolder graphQLSchemaHolder() {
            return graphQLSchemaBuilder().buildSchema(TodoSchema.class);
        }
    }

Executing queries async:

        RxExecutionResult result = GraphQLQueryExecutor
                                             .create(graphQLSchemaHolder)
                                             .query("{viewer{ id }}")
                                             .execute();
        // work with execution result

Executing queries async with concurrent fields resolution (see GraphQLQueryExecutor.forkJoinExecutorService() or GraphQLQueryExecutor.forkJoinExecutorService(int parallelism)):


        GraphQLRxExecutionResult result =
                GraphQLQueryExecutor.builder()
                        .create(graphQLSchemaHolder)
                        .forkJoinExecutorService()
                        .query("{viewer{ id }}")
                        .execute();

check GraphQLQueryExecutor class to find more ways how to run queries.

Schema build process can be customized using com.oembedler.moon.graphql.engine.GraphQLSchemaConfig:


    private String clientMutationIdName = "clientMutationId";
    private boolean injectClientMutationId = true;
    private boolean allowEmptyClientMutationId = false;
    private String mutationInputArgumentName = "input";
    private String outputObjectNamePrefix = "Payload";
    private String inputObjectNamePrefix = "Input";
    private String schemaMutationObjectName = "Mutation";
    private boolean dateAsTimestamp = true;
    private String dateFormat = "yyyy-MM-dd'T'HH:mm'Z'";

    // there will be more config options added in the future

Protection Against Malicious Queries

Since typical GraphQL schemas contain recursive types and circular dependencies, clients are able to send infinitely deep queries which may have high impact on server performance. The library provides two mechanisms to protect your GraphQL server from malicious or too expensive queries.

Query Complexity Analysis

Query complexity analysis makes an estimation of the query complexity during execution. The complexity is Double number that is calculated according to the simple rule described below. Every field in the query gets a default score 1.0 (including GraphQLObjectType nodes). The complexity of the query is the sum of all field scores.

    public Integer getFirstDefaultValue() {
        return 1;
    }

    public Integer getLastDefaultValue() {
        return 1;
    }

    // `before`, `after`, `first`, `last` and `childScore` are avaliable in SpEL expression
    @GraphQLField
    @GraphQLComplexity("1 + first * #childScore")
    public TodoConnectionObjectType todos(@GraphQLIn(value = "before") String before,
                                          @GraphQLIn(value = "after") String after,
                                          @GraphQLIn(value = "first", defaultProvider = "getFirstDefaultValue") Integer first,
                                          @GraphQLIn(value = "last", defaultProvider = "getLastDefaultValue") Integer last) {

        // implementation ommitted for the sake of simplicity        

        return todoConnectionObjectType;
    }

Note that above example has GraphQLComplexity annotation value is a Spring SpEL expression. This annotation can be used to customize complexity calculation for a node. SpEL expression context has field input parameters and childScore parameter which is sum of all child fields scores.

To set maxQueryComplexity use GraphQLQueryExecutor:

   GraphQLQueryExecutor.create(graphQLSchemaHolder).maxQueryComplexity(1500);

The query complexity algorithm is dynamic so typical introspection query doesn't have static permanent complexity - having more fields definitions, arguments and objects in a schema causes complexity to grow.

During execution when maximum query complexity reached - library throws an QueryComplexityLimitExceededRuntimeException exception.

Limiting Query Depth

Limiting query depth can be done by providing the maxQueryDepth argument to the GraphQLQueryExecutor:

GraphQLQueryExecutor.create(graphQLSchemaHolder).maxQueryDepth(4);

When maximum query depth is reached library does not throw any exception but returns null for unresolved field(s).

Relay Support

Library adds abstractions for the Relay support. Please look at the tests for TodoSchema for an example. There are ways how to extend Relay classes to get custom behaviour.

Some tips:

@GraphQLObject("Todo")
public class TodoObjectType extends BaseObjectType {

    // fields definitions are omitted for clarity 

    @GraphQLObject
    public static class TodoEdgeObjectType extends EdgeObjectType<TodoObjectType> {
    
      // `EdgeObjectType` is generic class that can be extended to add custom behaviour
      
    }

    @GraphQLObject
    public static class TodoConnectionObjectType extends ConnectionObjectType<TodoEdgeObjectType, PageInfoObjectType> {
    
    // `ConnectionObjectType` is generic class that can be extended to add custom behaviour
    
    }
}

Node interface (given schema uses proper hierarchy of objects):


// defined in library `relay` package
@GraphQLInterface("Node")
public interface RelayNode {

    @GraphQLID("id")
    @GraphQLNonNull
    @GraphQLDescription("GraphQL Relay global object unique identifier")
    String getId(RelayNode relayNode);
}

All custom objects implement that interface through intermediate base class (no need to implement default bahaviour in each class):

public class BaseObjectType implements RelayNode {

    @GraphQLIgnore
    private String id;

    @GraphQLID("id")
    @GraphQLNonNull
    @GraphQLDescription("Global object unique identifier")
    public String getId(RelayNode relayNode) {
        BaseObjectType baseObjectType = (BaseObjectType) relayNode;
        
        // `id` can be encoded into base64 if opaque value is required
        
        return baseObjectType.id;
    }
}

Data resolver is defined in a root object query as follows:

@GraphQLObject("Root")
public class RootObjectType {

    @GraphQLField
    public RelayNode node(@GraphQLID @GraphQLNonNull @GraphQLIn("id") final String id) {
    
        // data resolver by global ID goes here
        
        return null;
    }
    
}

Relay ConnectionArguments can be passed in multiple ways to a data resolver.

    @GraphQLField
    public TodoConnectionObjectType todos(@GraphQLIn(value = "before") String before,
                                          @GraphQLIn(value = "after") String after,
                                          @GraphQLIn(value = "first") Integer first,
                                          @GraphQLIn(value = "last") Integer last) {}

Complex (nested) input objects are also supported.

    public class RelayConnectionArguments {
        public String before;
        public String after;
        public Integer first;
        public Integer last;
        // ...
    }

    @GraphQLField
    public TodoConnectionObjectType todos(@GraphQLIn("connArgs") RelayConnectionArguments) {
         // when query for a data arguments must be passed as embedded input argument `connArgs` 
         // { ... todos(connArgs{first: 10}){...} ... }
    }

Note using wrapper object for arguments make them surface from that wrapper node but not from input root.

In general the library does not force to build Relay compliant schemas - it's up to developer to decide if this compatibility should be maintained.

Contributions

Contributions are welcome.

Tips:

Acknowledgment

This implementation is based on the java reference implementation. For example the TodoSchema and the tests (among a lot of other things) are simply adapted to use with library code.

License

spring-graphql-common is licensed under the MIT License. See LICENSE for details.

graphql-java License

graphql-js License