How to connect to gridFS?
I'm trying to implement apollo-upload-server (which is exactly what I'm needing) using gridFS. So I came up to https://github.com/jaydenseric/apollo-upload-server/issues/8#issuecomment-312974127

But I've some problems how to get connected to the db at all in my express server (do I have to use middleware?), which looks like this:

```javascript
import express from 'express'
import { graphqlExpress, graphiqlExpress } from 'apollo-server-express'
import { apolloUploadExpress } from 'apollo-upload-server'
import crossOriginRequests from './middlewares/cors'
import schema from './graphql/schema'

const app = express()

app.use('/graphql',
  bodyParser.text({ type: 'application/graphql' }),
  crossOriginRequests,
  apolloUploadExpress(),
  graphqlExpress(req => ({
    schema: schema,
    context: { token: req.headers.authorization }
  }))
)

app.listen(port, () => {
  if (process.env.NODE_ENV !== 'production') {
    console.log('Listening on port ' + port)
  }
})

export default app
```
In my resolver I would like to write the stream:

```javascript
import { GraphQLUpload } from 'apollo-upload-server'

const processUpload = async upload => {
  const { stream, filename, mimetype, encoding } = await upload

  // use gfs here to write stream...

  return { id, filename, mimetype, encoding }
}

export default {
  Upload: GraphQLUpload,
  Mutation: {
    singleUpload: (obj, { file }) => processUpload(file)
  }
}
```
