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:

``js
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

`sh
npm install graphql-fields-projection
`

How to

Please see the following examples

$3

Given the following query

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

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

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

$3

Given the following query

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

`js
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'
}
`

$3

Given the following query

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

`js
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'
}
`

$3

> 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

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

`js
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 }
}
`

$3

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

`js
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