graphql-dataloader-mongoose is a DataLoader generator library that creates a new DataLoader based on an existing Mongoose model with a single line of code!
npm install graphql-dataloader-mongoose
var DataLoader = require('graphql-dataloader-mongoose')
var dataloaderFactory = new MongooseDataloaderFactory();Start by creating a new MongooseDataloaderFactory.
MongooseDataloaderFactory can create a Mongoose DataLoader instance dynamically while the application is running.
The instance can then create any DataLoader related to a designated Mongoose model (to be explained in detail below).
For example, here is a Mongoose model representing a User collection in a MongoDB instance.
var UserModel = mongoose.model('User', new Schema({ userId: String, name: String})You can create a DataLoader which can fetch user data by a userId key.
var userIdDataloader = dataloaderFactory.mongooseLoader(UserModel).dataloader('userId');Let's see how it works in detail!
We create a Mongoose DataLoader instance by passing UserModel into dataloaderFactory.mongooseLoader().
Then, we can create any DataLoader derived from the UserModel key.
var userMongooseDataloader = dataloaderFactory.mongooseLoader(UserModel);To use a DataLoader which selects data using the userId key,
all you need to do is pass the key to MongooseDataloader.dataloader().
var userIdDataloader = userMongooseDataloader.dataloader('userId');In this example, userIdDataloader can load data from the User collection,
using userId parameters in userIdDataloader.load() or userIdDataloader.loadMany().
For more information on DataLoader functions and usage, please refer to https://github.com/graphql/dataloader#batch-function.
The code for userIdDataloader is roughly equivalent to the following:
var userIdDataloader = new DataLoader(ids =>
this.userModel.find({ userId: { $in: ids } }).then(list => {
var listByKey = _.keyBy(list, key);
return ids.map(id => _.get(listByKey, id, null));
}),
);If you need another DataLoader that selects data from UserModel using a different key, e.g. _id, just pass _id instead of userId to userDataloader.dataloader().
var userPkDataloader = userDataloader.dataloader('_id');If you want to keep the code simple as possible, you can chain everything in a single line of code:
var userIdDataloader = dataloaderFactory.mongooseLoader(UserModel).dataloader('userId');just call load() or loadMany() just like you use the original DataLoader.
var userIds = ['John', 'Min', 'Lark'];
userIdDataloader.load(userIds).then(user => console.log(user.name));graphql-dataloader-mongoose integrates well with Apollo Server.
To use with Apollo Server, pass a MongooseDataLoaderFactory instance to the Apollo context when you initialize ApolloServer.
MongooseDataloaderFactory() to the context function in the configuration parameters for ApolloServer, because a new DataLoader should be created in every HTTP request. (See Caveats)
var apolloServer = new ApolloServer( {
schema: yourSchema,
context: async ctx => {
var dataloaderFactory = new MongooseDataloaderFactory();
return { ...ctx, dataloaderFactory };
},
})Then, in the resolver function, you can use the MongooseDataLoaderFactory instance assigned in Apollo context:
Query: {
resolveUserById(parent, param, context) {
var userIds = param.userIds;
var dataloaderFactory = context.dataloaderFactory;
var userIdDataloader = dataloaderFactory.mongooseLoader(userModel).dataloader('userId');
return userIdDataloader.loadMany(userIds);
}
}graphql-dataloader-mongoose is a TypeScript-based library.
Projects using TypeScript can easily incorporate it into their existing type system.
For example, suppose UserModel has IUserModel as an interface.
interface IUser {
userId: string;
name: string;
}
interface IUserModel extends IUser, Document {}
const UserModel = mongoose.model<IUserModel>(
'User',
new Schema({ userId: String, name: String }),
);You can create a DataLoader by passing the interface, a la
dataloaderFactory.mongooseLoader<IUserModel>.
const userId = 'John';
const dataloaderFactory = new MongooseDataloaderFactory();
// assign IUserModel interface in mongooseLoader function generic type
const userIdDataloader = dataloaderFactory
.mongooseLoader<IUserModel>(userModel)
.dataloader('userId');
// able to typecheck user model attribute (name, userId ..)
const user = userIdDataloader.load(userId);You must always create a new MongooseDataloaderFactory() in every request. It is insufficient to set an instance as a global variable.
Pleas refer to https://github.com/graphql/dataloader#creating-a-new-dataloader-per-request for more details.
Currently, graphql-dataloader-mongoose only supports finding by key (find( key : { $in : ids}})
Support for other queries will be added soon.
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