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// MANY-TO-MANY — students and courses db.students.insertOne({ _id: ObjectId("s1"), name: "Dana", // Array of references enrolledCourseIds: [ObjectId("c1"), ObjectId("c2"), ObjectId("c3")] }) // Find all students enrolled in course c1 db.students.find({ enrolledCourseIds: ObjectId("c1") }) // TREE — ancestors array pattern (category hierarchy) db.categories.insertMany([ { _id: 1, name: "Root", ancestors: [] }, { _id: 2, name: "Electronics", ancestors: [1] }, { _id: 3, name: "Laptops", ancestors: [1, 2] }, { _id: 4, name: "Gaming", ancestors: [1, 2, 3] } ]) // Find all descendants of Electronics (id=2) db.categories.find({ ancestors: 2 }) // Materialised path pattern db.categories.insertOne({ _id: 5, name: "Ultrabooks", path: "/1/2/3/5" // full path string }) // Find all nodes under Electronics using regex db.categories.find({ path: /^\/1\/2/ })
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