A document from the books collection looks like:
{
_id: '0395623650',
title: 'Platero y yo / Platero and I (Spanish-English Bilingual Edition) (English and Spanish Edition)',
authors: [
{
_id: '64cc2db4830ba29148db5180',
name: 'Juan Ramón Jiménez'
}
],
pages: 64,
year: 1994,
synopsis: 'Selections from a classic of world literature present a picture of life in the town of Moguer, in Andalusia, Spain.\n' +
'\n' +
'\n' +
' Presents a picture of life in the town of Moguer, in Andalusia, Spain, as seen through the eyes of a wandering poet and his faithful donkey.\n',
cover: 'https://images.isbndb.com/covers/36/57/9780395623657.jpg',
attributes: [
{
key: 'edition',
value: 'F First Edition Thus'
},
{
key: 'dimensions',
value: 'Height: 10.499979 Inches, Length: 6.999986 Inches, Weight: 2.0502990366 Pounds, Width: 0.12499975 Inches'
},
{
key: 'isbn13',
value: '9780395623657'
},
{
key: 'msrp',
value: 1.99
},
{
key: 'isbn',
value: '0395623650'
},
{
key: 'isbn10',
value: '0395623650'
}
],
totalInventory: 1,
available: 1,
binding: 'Hardcover',
language: 'en',
longTitle: 'Platero y yo / Platero and I (Spanish-English Bilingual Edition) (English and Spanish Edition)',
publisher: 'Clarion Books'
}
If we're interested just in the titles, we can use $project to select just the fields we're interested in. As an example, to get just the book's title and year we'll write:
If we're interested in the titles, we can use $project to select just the fields we're interested in. As an example, to get just the book's title and year, we'll write:
[
{
$project: {title: 1, year: 1}
}
]
db.books.aggregate([{$project: {title: 1, year: 1}}])
_id field is shown by default_id field is shown by default.So we can exclude fields and show all fields except attributes using:
[
{
$project: {attributes: 0}
}
]
db.books.aggregate([{$project: {attributes: 0}}])
👐 Show only title and cover.
[
{
$project: {title: 1, cover: 1}
}
]
db.books.aggregate([{$project: {title: 1, cover: 1}}])
👐 Exclude the cover, attributes and _id fields from the result.
👐 Exclude the cover, attributes, and _id fields from the result.
[
{
$project: {_id: 0, attributes: 0, cover: 0}
}
]
db.books.aggregate([{$project: {_id: 0, attributes: 0, cover: 0}}])
You can't include and exclude fields in the same projection: if you start including, you must keep including and vice versa.
You can't include and exclude fields in the same projection. If you start including, you must keep including, and vice versa.
For instance, this will fail:
db.books.aggregate([{$project: {title: 1, attributes: 0}}])
MongoServerError: Invalid $project :: caused by :: Cannot do exclusion on field attributes in inclusion projection
The only exception to this rule is the _id field, which we can exclude in an inclusion projection.