graphql-fields-projection

GraphQL Fields Projection

This library create field projection from GraphQL query

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

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

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

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

resolve(parent, args, context, info){
  const resultArray1 = createSelectedFields(info); // [ 'id', 'address', 'info.firstName', 'info.lastName' ]
  const resultArray2 = createSelectedFields(info, { returnType : 'array' }); // [ 'id', 'address', 'info.firstName', 'info.lastName' ]
  const resultString = createSelectedFields(info, { returnType : 'string' } ); // 'id address info.firstName info.lastName'
  const resultObject = createSelectedFields(info); // { id: 1, address: 1, 'info.firstName': 1, 'info.lastName': 2 }
}

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');

__resolveReference(parent, context, info) {
  const { loaders } = context;
  const selectedFields = createSelectedFields(info);
  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