我试图映射两个集合（产品，订单）。它成功地映射并在mongodb中获取数据。但是我对集合产品和集合订单感到怀疑。我只希望在产品表中映射一个字段，而不是整个记录。如何实现这种场景。
product_collection
{
"_id": "5cebbba456790623d0e45ca7",
"product_name": "iBall Baton 150M Wireless-N Mini USB Adapter (iB-WUA 150NM)",
"product_image": [
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SY450_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX569_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SY355_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX522_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX679_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX425_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX466_.jpg"
],
"product_description": "Enhanced 150mbps wireless data transmission rate. With 64 128 bit WEP WPA and WPA2 PSK wireless security support infrastructure and AD HOC operation mode USB 2.0 High speed interface bundled utility helps simple configuration and easy monitoring.",
"product_overview": "Unique design allows easy access to all buttons controls & ports. The low profile construction makes this the slimmest tpu ipad mini mini 2 case on the market case. Color: optionalas pictures show.",
"product_specification": [
{
"brand": "iBall",
"colour": "Black",
"item_height": "13 Millimeters",
"item_width": "13.4 Centimeters",
"item_weight": "40.8 g",
"product_dimensions": "12.1 x 13.4 x 1.3 cm",
"item_model_number": "iB-WUA150NM"
}
],
"warranty": "Limited Warranty period (parts): 1 year",
"old_price": "440",
"new_price": "380",
"category_id": "5cee1140753bd210b8a291c3",
"discount": 10,
"features": [
{
"deals_of_the_day": true
}
],
"promotional_tags": [
1,
2,
3
]
}
order_collection
{
"_id": "5cee1140753bd210b8a291c3"
"name":"bourbon"
}
映射代码
db.product.aggregate([{$lookup:{
from:'order',
localField:'category_id',
foreignField:'_id',
as:'ordersetails'
}},{$project:{product_description:0,product_overview:0,product_specification:0,category_id:0,features:0,promotional_tags:0,warranty:0,old_price:0,new_price:0,discount:0}}])
我得到了输出
{
"_id": "5cebbba456790623d0e45ca7"
"product_name": "iBall Baton 150M Wireless-N Mini USB Adapter (iB-WUA 150NM)",
"product_image": [
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SY450_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX569_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SY355_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX522_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX679_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX425_.jpg",
"https://images-na.ssl-images-amazon.com/images/I/41k-UNigbyL._SX466_.jpg"
],
"ordersetails":{
"_id": "5cee1140753bd210b8a291c3"
"name":"bourbon"
}
}
例外输出
{
"_id": "5cebbba456790623d0e45ca7"
"product_name": "iBall Baton 150M Wireless-N Mini USB Adapter (iB-WUA
150NM)",
"product_image": "https://images-na.ssl-images-amazon.com/images/I/41k-
UNigbyL._SY450_.jpg",
"ordersetails":"bourbon"
}