One-to-One, One-to-Many और Many-to-Many
Relationships embedding से या ids store करके model होते हैं, कितने items involved हैं इसके आधार पर।
In this page:
One-to-One/One-to-Many/Many-to-Many
One-to-one: embed करें। One-to-few: एक array embed करें। One-to-many: many side से reference करें या अगर bounded हो तो embed करें। One-to-squillions: हर child में parent id store करें। Many-to-many: एक या दोनों sides पर ids के arrays, या एक linking collection।
Note:
बड़ी counts वाले one-to-many के लिए, child documents में parent id रखें।
उदाहरण: One-to-one/one-to-many/many-to-many
test> db.students.insertMany([{ _id: 1, name: "Ada", courseIds: [10, 11] }, { _id: 2, name: "Bob", courseIds: [11] }])
{ acknowledged: true, insertedIds: { '0': 1, '1': 2 } }
test> db.courses.insertMany([{ _id: 10, title: "Math" }, { _id: 11, title: "Code" }])
{ acknowledged: true, insertedIds: { '0': 10, '1': 11 } }
test> db.students.aggregate([{ $lookup: { from: "courses", localField: "courseIds", foreignField: "_id", as: "courses" } }, { $project: { _id: 0, name: 1, courses: "$courses.title" } }])
[
{ name: 'Ada', courses: [ 'Math', 'Code' ] },
{ name: 'Bob', courses: [ 'Code' ] }
]⚠️ Run this in your own terminal or Node.js environment.
Related Topics
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आम गलतियां
- Unbounded children embed करना
- हमेशा बढ़ने वाले id arrays store करना
- reference fields index करना भूल जाना
चैप्टर सारांश
- One-to-one embed करें
- One-to-few arrays embed करें
- One-to-many parent reference करें
- Many-to-many id arrays इस्तेमाल करें
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