4. Create and demonstrate how projection operators ($, $elematch and $slice) would be used in the MongoDB.
use retailDBdb.Products.insertMany([
{
name: "Laptop",
brand: "BrandA",
features: [
{ name: "Processor", value: "Intel i7" },
{ name: "RAM", value: "16GB" },
{ name: "Storage", value: "512GB SSD" }
],
reviews: [
{ user: "Alice", rating: 5, comment: "Excellent!" },
{ user: "Bob", rating: 4, comment: "Very good" },
{ user: "Charlie", rating: 3, comment: "Average" }
]
},
{
name: "Smartphone",
brand: "BrandB",
features: [
{ name: "Processor", value: "Snapdragon 888" },
{ name: "RAM", value: "8GB" },
{ name: "Storage", value: "256GB" }
],
reviews: [
{ user: "Dave", rating: 4, comment: "Good phone" },
{ user: "Eve", rating: 2, comment: "Not satisfied" }
]
}
])Use Projection Operators:
1. $ Projection Operator: Find the product named “Laptop” and project the review from the user “Alice”.
db.Products.find(
{ name: "Laptop", "reviews.user": "Alice" },
{ "reviews.$": 1 }
).pretty()OUTPUT:
[
{
_id: ObjectId('666c2f237d3bfa1feacdce05'),
reviews: [ { user: 'Alice', rating: 5, comment: 'Excellent!' } ]
}
]2. $elemMatch Projection Operator: Find the product named “Laptop” and project the review where the rating is greater than 4.
db.Products.find(
{ name: "Laptop" },
{ reviews: { $elemMatch: { rating: { $gt: 4 } } } }
).pretty()OUTPUT:
[
{
_id: ObjectId('666c2f237d3bfa1feacdce05'),
reviews: [ { user: 'Alice', rating: 5, comment: 'Excellent!' } ]
}
]3. $slice Projection Operator: Find the product named “Smartphone” and project the first review.
db.Products.find(
{ name: "Smartphone" },
{ reviews: { $slice: 1 } }
).pretty()OUTPUT:
[
{
_id: ObjectId('666c2f237d3bfa1feacdce06'),
name: 'Smartphone',
brand: 'BrandB',
features: [
{ name: 'Processor', value: 'Snapdragon 888' },
{ name: 'RAM', value: '8GB' },
{ name: 'Storage', value: '256GB' }
],
reviews: [ { user: 'Dave', rating: 4, comment: 'Good phone' } ]
}
]