GraphQL Fields Projection

• Why using this?
• Install
• How to
  • Example 1: simplest usecase
  • Example 2: Get more fields
  • Example 3: Get child path
  • Example 4: returnTypes
  • Example 5: Using with Dataloader

This library create field projection from GraphQL query

NOTE: Since version 1.1.0 the default returnType is string

Why using this?

There are many libraries can do the same function. However, starting in MongoDB 4.4, the Path Collision Restrictions are introduced . And it is illegal to project an embedded document with any of the embedded document's fields:

db.inventory.find({}, { size: 1, "size.uom": 1 }); // Invalid starting in 4.4

• And this library is created to remove the collision.
• This library can work with dataloader also

Install

npm install graphql-fields-projection

How to

Please see the following examples

Example 1: simplest usecase

Given the following query

query user {
  user(id: 123) {
    id
    address
    info {
      firstName
      lastName
    }
  }
}

const { createSelectedFields } = require('graphql-fields-projection');

resolve(parent, args, context, info){
  const selectedFields = createSelectedFields(info); // 'id address info.firstName info.lastName'
}

Example 2: Get more fields

Given the following query

query user {
  user(id: 123) {
    id
    address
    info {
      firstName
      lastName
    }
  }
}

const { createSelectedFields } = require('graphql-fields-projection');

resolve(parent, args, context, info){
  // Now you like to get more fields for further resolve: `timezone`, and `info` object
  const selectedFields = createSelectedFields(info, { additionalFields: ['info', 'address', 'timezone'] }); // 'id info timezone'
}

Example 3: Get child path

Given the following query

query purchase {
  purchase(id: 123) {
    id
    buyer {
      id
      address
      info {
        firstName
        lastName
      }
    }
    product {
      id
      # ...others
    }
  }
}

const { createSelectedFields } = require('graphql-fields-projection');

resolve(parent, args, context, info){
  // Now you like to get selected fields of `buyer`
  const selectedFields = createSelectedFields(info, { path: 'buyer' }); // 'id address info.firstName info.lastName'

  // OR with additionalFields
const selectedFields2 = createSelectedFields(info, {
  path: 'buyer', additionalFields: ['info', 'address', 'timezone'],
}); // 'id info timezone'
}

Example 4: returnTypes

NOTE: Since version 1.1.0 the default returnType is string

By the default the return result will be an string of projected fields. But you can also get the array or object

query user {
  user(id: 123) {
    id
    address
    info {
      firstName
      lastName
    }
  }
}

const { createSelectedFields } = require('graphql-fields-projection');

resolve(parent, args, context, info){
  const resultString = createSelectedFields(info); // 'id address info.firstName info.lastName'
  const resultString = createSelectedFields(info, { returnType : 'string' } ); // 'id address info.firstName info.lastName'
  const resultArray2 = createSelectedFields(info, { returnType : 'array' }); // [ 'id', 'address', 'info.firstName', 'info.lastName' ]
  const resultObject = createSelectedFields(info, { returnType : 'object' }); // { id: 1, address: 1, 'info.firstName': 1, 'info.lastName': 1 }
}

Example 5: Using with Dataloader

query purchase {
  purchase(id: 123) {
    id
    buyer {
      id
      address
      info {
        firstName
        lastName
      }
    }
    products {
      id
      sku
      name
      price
    }
  }
}

const { createSelectedFields, createMergedSelectedFields } = require('graphql-fields-projection');

// This is an example with Apollo Federation, but you can run with any resolvers
__resolveReference(parent, context, info) {
  const { loaders } = context;
  const selectedFields = createSelectedFields(info, { returnType : 'array' });
  return loaders.product.load(JSON.stringify({ id: parent.id, selectedFields }));
}

// The implementation of `loaders.product()`
async function batchProducts(keys) {
  const { ids: productIds, selectedFields } = createMergedSelectedFields(keys);
  const products = await Product.find({ _id: { $in: productIds } })
    .select(selectedFields)
    .lean();

  // Don't forget mapping results
  // ...

  return products;
}

The function createMergedSelectedFields() supports the following options:

• additionalFields
• returnType