[英]MongoDB update field with another field from another collection
我有兩個 collections:書籍和類別。 類別 collections 表示樹結構,使它們使用父級和子級嵌套類別。
這本書可以有多個類別並將它們存儲在一個數組中。
示例:圖書具有類別,我想將其停用並將其設置為父類別。
這就是類別集合的填充方式。
db.categories.insertMany([
{
_id: "Space Opera",
ancestors: ["Science Fiction", "Fiction", "Science Fiction & Fantasy"],
parent: ["Science Fiction"],
},
{
_id: "Dystopian",
ancestors: ["Science Fiction", "Fiction", "Science Fiction & Fantasy"],
parent: ["Science Fiction"],
},
{
_id: "Cyberpunk",
ancestors: ["Science Fiction", "Fiction", "Science Fiction & Fantasy"],
parent: ["Science Fiction"],
},
{
_id: "Science Fiction",
ancestors: ["Fiction", "Science Fiction & Fantasy"],
parent: ["Fiction", "Science Fiction & Fantasy"],
},
{
_id: "Fantasy",
ancestors: ["Science Fiction & Fantasy"],
parent: ["Science Fiction & Fantasy"],
},
{
_id: "Science Fiction & Fantasy",
ancestors: [],
parent: [],
},
{
_id: "Fiction",
ancestors: [],
parent: [],
},
]);
另外,我如何查詢這個並只獲取值“科幻小說”(注意它存儲在一個數組中)?
db.categories.find({_id : "Space Opera"}, {_id : 0, parent : 1})[0].parent // Did not work
db.categories.find({_id : "Space Opera"}, {_id : 0, parent : 1}) // find parent
// result
[
{
"parent": [
"Science Fiction"
]
}
]
db.books.update(
{title : "Book1"},
{$set : {category : [**PARENT CATEGORY**]}}
)
我相信我可以在 books.update() 中使用上面的代碼
我可以將它存儲在一個單獨的變量中,但在 vscode 中它給了我未定義的。 內部查詢並沒有像前面所說的那樣給我正確的值,但我認為你明白了。
db.books.update(
{title : "Book1"},
{$set : {category : [db.categories.find({_id : "Space Opera"}, {_id : 0, parent : 1})]}}
)
您可以使用此聚合管道獲得的父級:
db.categories.aggregate([
{ $match: { _id: "Space Opera" } },
{ $project: { _id: 0, parent: { $first: "$parent" } } }
])
甚至
db.categories.aggregate([
{ $match: { _id: "Space Opera" } },
{ $project: { _id: 0, parent: { $first: "$parent" } } }
]).toArray().shift().parent
要加入 collections,您必須使用$lookup運算符。 請記住,NoSQL 數據庫(如 MongoDB)未針對連接/查找進行優化。 在現實生活中,您應該尋找更好的設計。
db.books.aggregate([
{ $match: { title: "Book1" } },
{
$lookup:
{
from: "categories",
pipeline: [
{ $match: { _id: "Space Opera" } },
{ $project: { _id: 0, parent: { $first: "$parent" } } }
],
as: "category"
}
},
{ $set: { category: { $first: "$category.parent" } } }
])
如果您想更新現有集合,則必須為其創建一個循環:
db.books.aggregate([...]).forEach(function (doc) {
db.books.updateOne({ _id: doc._id }, { $set: { category: doc.category } });
})
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