add database and service

Author: monica.lopez-gris

documentation/guides-grapql.asciidoc

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+:caution-caption: :fire:
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+:listing-caption: Listing
+
+= GraphQL on Devon4Node
+
+=== Database setup
+
+First of all we are going to setup a mongo database to work with, we are not going to get in details with this so you can go to the  https://docs.nestjs.com/techniques/mongodb[Nestjs documentation] to find more.
+
+First we need to install a couple of dependencies:
+
+[source,bash]
+----
+yarn add @nestjs/mongoose mongoose
+yarn add -D @types/mongoose
+----
+
+And add MongooseModule to `app.module.ts`
+
+[source,typescript]
+----
+import { Module } from '@nestjs/common';
+import { MongooseModule } from '@nestjs/mongoose';
+
+@Module({
+  imports: [
+    MongooseModule.forRoot('mongodb://localhost:27017'),
+  ],
+})
+export class AppModule {}
+----
+
+Now let's create our schema, inside `todos/schemas` we are going to create a file `todo.schema.ts` with: 
+
+[source,typescript]
+----
+import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
+import { Document } from 'mongoose';
+
+@Schema()
+export class Todo extends Document {
+  @Prop()
+  id: number;
+
+  @Prop()
+  task: string;
+
+  @Prop()
+  status: boolean;
+}
+
+export const TodoSchema = SchemaFactory.createForClass(Todo);
+----
+
+Then import it on `todo.module.ts`.
+
+[source,typescript]
+----
+import { Module } from '@nestjs/common';
+import { MongooseModule } from '@nestjs/mongoose';
+import { Todo, TodoSchema } from './schemas/todo.schema';
+
+@Module({
+  imports: [MongooseModule.forFeature([{ name: Todo.name, schema: TodoSchema }])]
+})
+export class TodosModule {}
+----
+
+=== Service
+
+To interact with the database we need a service, first we create a module with `devon4node generate module todos` and inside create the service `todos.service.ts`.
+
+[source,typescript]
+----
+import { Injectable } from '@nestjs/common';
+import { InjectModel } from '@nestjs/mongoose';
+import { Model } from 'mongoose';
+import { Todo } from './schemas/todo.schema';
+
+@Injectable()
+export class TodosService {
+  constructor(@InjectModel(Todo.name) private readonly todoModel: Model<Todo>) {}
+
+  async create(task: string): Promise<Todo> {
+    const object = {
+      task: task
+    }
+    const createdTodo = new this.todoModel(object);
+    return createdTodo.save();
+  }
+
+  async findAll(): Promise<Todo[]> {
+    return this.todoModel.find().exec();
+  }
+}
+----
+
+To finish this section we need to create the corresponding schema on `todos/schemas/todo.schema`:
+
+[source,typescript]
+----
+import { Prop, Schema, SchemaFactory } from '@nestjs/mongoose';
+import { Document } from 'mongoose';
+
+@Schema()
+export class Todo extends Document {
+  @Prop()
+  id: number;
+
+  @Prop()
+  task: string;
+
+  @Prop()
+  status: boolean;
+}
+
+export const TodoSchema = SchemaFactory.createForClass(Todo);
+----
+
+=== GraphQL
+
+To install it:
+
+[source,bash]
+----
+yarn add @nestjs/graphql graphql-tools graphql apollo-server-express
+----
+
+=== Squema first
+This tutorial uses the schema first method.
+
+First we need to import GraphQLModule to our `app.module.ts`.
+
+[source,typescript]
+----
+...
+import { GraphQLModule } from '@nestjs/graphql';
+import { join } from 'path';
+
+@Module({
+  imports: [
+    ...
+    GraphQLModule.forRoot({
+      typePaths: ['./**/*.graphql'],
+      definitions: {
+        path: join(process.cwd(), 'src/graphql.ts'),
+        outputAs: 'class',
+      },
+    }),
+  ],
+})
+export class AppModule {}
+----
+
+The `typePaths` indicates the location of the schema definition files.
+
+The `definitions` indicates the file where the typescript definitions, adding the `outputAs: 'class'` saves those definitions as classes.
+
+==== Resolver
+
+Resolvers has the instructions to turn graphQL orders into the data requested.
+
+To create a resolver we go to todos module and then create a new `todos.resolver.ts` file, import the decorators needed and set our resolver.
+
+[source,typescript]
+----
+import { Resolver, Args, Mutation, Query } from '@nestjs/graphql';
+import { TodosService } from './services/todos.service';
+import { Todo } from './schemas/todo.schema';
+
+@Resolver()
+export class TodosResolver {
+  constructor(private readonly todosService: TodosService) {}
+
+  @Query()
+  findAll(): Promise<Todo[]> {
+    return this.todosService.findAll();
+  }
+  @Mutation()
+  createTodo(@Args('task') task: string): Promise<Todo> {
+    return this.todosService.create(task);
+  }
+}
+
+----
+
+`@Resolver()` indicates that the next class is a resolver.
+
+`@Query` is used to get data.
+
+`@Mutation` is used to create or modify data.
+
+The `@mutation` will create the next schema in or autogenerated schema file:
+[source,typescript]
+----
+type Mutation {
+    createTodo( task: String ): Todo
+}
+----
+
+And the `@Query` would do the same:
+[source,typescript]
+----
+type Query {
+    todos: [Todo]
+}
+----
+
+Here we have also an argument decorator `@Args` which is an object with the arguments passed into the field in the query.
+
+Learn more about resolvers and their argument decorators on the https://docs.nestjs.com/graphql/resolvers#schema-first[NestJS documentation].
+
+
+
+=== Code first
+On this approach we are going to use decorators to generate de schema.

samples/graphql-schema-first

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