project.md

Project Stage

In this stage, you can make sure that only the specific fields are returned for each item in your list.

This stage follows this pattern: { fields: [<field>] }.

Consider the following data set:

[
  {
    title: 'abc',
    tags: ['x', 'y'],
    author: 'John'
  },
  {
    title: 'xyz',
    tags: ['x', 'a'],
    author: 'Donna'
  },
  {
    title: 'def',
    tags: ['a', 'b'],
    author: 'Gemma'
  }
]

{ fields: ['title', 'author'] }

will return the items with only the title and author fields present. The projection stage is always the last stage to run in the pipeline.

You can use any fields in all the other stages without an impact in your projection.

[{ title: 'abc', author: 'John' }, { title: 'xyz', author: 'Donna' }, { title: 'def', author: 'Gemma' }]

If you combine the alias in the transform stage with this stage, you need to add the old field name to the list of returned fields and not the new one.