GraphQL 學習心得

GraphQL

GraphQL - A Query Language for APIs

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GraphQL is a query language designed to build client applications by providing an intuitive and flexible syntax and system for describing their data requirements and interactions. — from Facebook

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Agenda

• Why GraphQL
• Java Library
• Example Project
• Problem
• GraphiQL

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Why GraphQL

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Overfetching

Downloading superfluous data

Overfetching means that a client downloads more information than is actually required in the app.

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Underfetching

Underfetching generally means that a specific endpoint doesn’t provide enough of the required information. The client will have to make additional requests to fetch everything it needs.

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Browser Connection Limit

Max Number of default simultaneous persistent connections per server/proxy:

Firefox 3+: 6
Opera 12: 6
Safari 5: 6
IE 7: 2
IE 8: 6
IE 10: 8
Chrome: 6

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HTTP connection cost

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REST vs GraphQL

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Java Library

Awesome graphql-java

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GraphQL and GraphiQL Spring Framework Boot Starters

Repository contains:

graphql-spring-boot-starter to turn your boot application into GraphQL server
graphiql-spring-boot-starter to embed GraphiQL tool for schema introspection and query debugging

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graphql-java-tools

com.coxautodev.graphql.tools.SchemaParser

Schema First

type Link {
  url: String!
  description: String!
}

type Query {
  allLinks: [Link]
}

schema.graphqls

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graphql-java-annotations

Code First

public class SomeObject {
  @GraphQLField
  public String field;
}

// ...
GraphQLObjectType object = GraphQLAnnotations.object(SomeObject.class);

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java-dataloader

DataLoader is a generic utility to be used as part of your application’s data fetching layer to provide a simplified and consistent API over various remote data sources such as databases or web services via batching and caching.

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Example Project

• GraphQLxSpringBoot
• GraphQLxSpringMVC

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GraphQLxSpringBoot

Spring Boot plugin requires Gradle 4.0 or later.

plugins {
    id 'org.springframework.boot' version '2.0.4.RELEASE'
}

apply plugin: 'java'
apply plugin: 'io.spring.dependency-management'

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web")
    compile group: 'com.graphql-java', name: 'graphql-spring-boot-starter', version: '4.0.0'
    compile group: 'com.graphql-java', name: 'graphiql-spring-boot-starter', version: '4.0.0'
}

gradle bootRun

http://localhost:8080/graphiql

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GraphQLxSpringMVC

dependencies {
    compile group: 'org.springframework', name: 'spring-webmvc', version: '4.3.16.RELEASE'
    compile group: 'com.graphql-java', name: 'graphql-java', version: '8.0'
    compile group: 'com.graphql-java', name: 'graphql-java-tools', version: '5.2.3'
}

gradle appRun

http://localhost:8080/GraphQLxSpringMVC/graphql

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Problem

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不支援泛型

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沒有 Inheritance

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沒有 Overload

a particular field must always return the same type

type Link {
  url: String!
  description: String!
}

type Query {
  links: [Link]
  links(limit: Int): [Link]
}

error

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Map Scalar

public class MapScalar {

  public static final GraphQLScalarType MAP = new GraphQLScalarType("Map", "A custom map scalar type", new Coercing() {
    @Override
    public Object serialize(Object dataFetcherResult) throws CoercingSerializeException {
      Map map = null;
      try {
        map = Map.class.cast(dataFetcherResult);
      } catch (ClassCastException exception) {
        throw new CoercingSerializeException("Could not convert " + dataFetcherResult + " into a Map", exception);
      }
      return map;
    }

    @Override
    public Object parseValue(Object input) throws CoercingParseValueException {
      return null;
    }

    @Override
    public Object parseLiteral(Object input) throws CoercingParseLiteralException {
      return null;
    }
  });
}

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Error(1)

status code always 200 even exception…

{
  "errors": [
    {
      "message": "Invalid Syntax",
      "locations": [
        {
          "line": 1,
          "column": 0
        }
      ]
    }
  ]
}

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Error(2)

{
  "data": {
    "Profile": null
  },
  "errors": [
    {
      "message": "Exception while fetching data (/Profile/basic) : Data Not Found, pid:3112122",
      "locations": [
        {
          "line": 3,
          "column": 5
        }
      ],
      "path": [
        "Profile",
        "basic"
      ]
    }
  ]
}

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GraphiQL

An in-browser IDE for exploring GraphQL.

autocomplete: option(control) + space

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Reference

https://facebook.github.io/graphql/June2018/
https://www.graphql-java.com/documentation/master/getting-started/

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