Is it possible to fetch data from multiple tables using GraphQLList

问题

In GraphQL we can write the object type in GraphQLList and fetch all the fields. I am using Association and it is joining the two tables but I am unable to fetch the field of both the tables. It only takes the fields what I have written in GraphQLList.As I want the list of data.

Here is the code

films table:

    module.exports =(sequelize, DataTypes) => {
  const films = sequelize.define(
    'films',
    {
      id:{
        type: DataTypes.INTEGER,
        primaryKey: true,
        allowNull: false,

      },
      name: {
        type: DataTypes.STRING,

      },
      },

  );

  films.associate = (models) => {


    films.hasMany(models.movie_stream, {
      foreignKey: 'movie_id',
    });

};

  return films;

}

movie_stream table:

    module.exports = (sequelize, DataTypes) => {
  const movie_streams = sequelize.define('movie_streams', {
    id:{
      type: DataTypes.INTEGER,
      primaryKey: true,
      allowNull: false,
    },
      movie_id: {
          type: DataTypes.STRING,
          foreignKey: "movie_id",

        },
     });

  movie_streams.associate = (models) => {

    movie_streams.hasMany(models.films, {
      foreignKey: 'id',
    });
  };

  return movie_streams;
};

Schema file:

movieList:{
      type: new GraphQLList(Films),
 resolve: (parent,args)=>{
return newdb.films.findAll({attributes:['id','name','permalink'],
where: {content_category_value:parent.id },
include: [{
    model:newdb.movie_stream,
    attributes:['id','movie_id'],
}],
}).then(data=>{
    return data;
})
}

Can I write here type: new GraphQLList(Films, MovieStream)??

I have tried but It does not work. Please give me some idea how do I fetch the fields of both the table???

回答1:

There's two main ways of achieving this in GraphQL: unions and interfaces.

An interface is where two or more object types in your GraphQL schema share certain fields (characteristics). For example you might have a Product interface for all the items in your shop, where every product has a price, barcode, and shelfLocation. All your products, such as Shampoo, Bread, LawnChair would then implement this interface.

interface Product {
  price: Float
  barcode: Int
  shelfLocation: ShelfLocation
}

type Bread implements Product {
  price: Float
  barcode: Int
  shelfLocation: ShelfLocation
  brand: String
  numberOfSlices: Int
  calories: Float
  bestBefore: Date
}

extend type Query {
  searchProducts(phrase: String!): [Product!]
}

A union is where you declare that something can return more than one object type, but those types don't have to have any properties in common.

type Shark {
  name: String
  numberOfTeeth: Int
}

type Shoe {
  brand: String
  size: String
}

union SharkOrShoe = Shark | Shoe

extend type Query {
  searchSharksAndShoes(phrase: String!): [SharkOrShoe!]
}

In both cases you can query type specific fields using fragments or inline fragments:

query {
  searchProducts(phrase: "tasty") {
    # shared fields
    __typename
    price
    barcode
    shelfLocation { aisle, position }

    # type specific fields
    ... on Bread { brand }
    ...breadFrag
  }
  searchSharksAndShoes(phrase: "sleek") {
    # only the introspection fields are shared in a union
    __typename

    # type specific fields
    ... on Shark { name, numberOfTeeth }
    ...shoeFrag
  }
}

fragment breadFrag on Bread {
  barcode
  bestBefore
}

fragment shoeFrag on Shoe {
  brand
  size
}

You can learn more about this in the GraphQL schema documentation and read about GraphQLInterfaceType and GraphQLUnionType in the GraphQL.js documentation.

来源：https://stackoverflow.com/questions/55117230/is-it-possible-to-fetch-data-from-multiple-tables-using-graphqllist