Piye cara nggawe hubungan (relationships) ing MongoDB?

Question

Accepted Answer

MongoDB nggawe hubungan (one-to-one, one-to-many, many-to-many) nganggo **embedding** utawa **referencing** — pilihan gumantung ing cardinality hubungan, cara data diakses, lan apa data iku dibagi. Beda karo SQL sing nganggo foreign key sing seragam, MongoDB menehi fleksibilitas kanggo saben hubungan.

## One-to-one

```js
// usually EMBED (the related data belongs to the document)
{ _id: ObjectId("..."), name: "Ann", profile: { bio: "...", avatar: "..." } }
// → one query gets both; they're accessed together
```

## One-to-many (paling umum — lan paling rumit)

```js
// ONE-TO-FEW → embed (bounded, accessed together)
{ _id: ObjectId("..."), name: "Ann", addresses: [ {...}, {...} ] }  // a few addresses

// ONE-TO-MANY → reference (the "many" side references the "one")
// authors collection: { _id: "a1", name: "Ann" }
// books collection:   { _id: "b1", authorId: "a1", title: "..." }  // each book references its author

// ONE-TO-SQUILLIONS (huge/unbounded) → ALWAYS reference (never embed unbounded data)
// e.g. a user with millions of log entries → separate collection, reference by userId
```

Nuansa penting: **one-to-few** (embed), **one-to-many** (reference saka sisi many), **one-to-squillions** (tansah reference — aja embed data tandhes wates, amarga wates dokumen 16MB lan masalah performa).

## Many-to-many

```js
// reference with an array of ids (on one or both sides)
{ _id: "s1", name: "Student", courseIds: ["c1", "c2"] }     // student → courses
{ _id: "c1", name: "Course", studentIds: ["s1", "s2"] }     // course → students (optional)
// → query and $lookup to resolve; or a separate "enrollments" collection (junction-like)
```

Many-to-many nganggo array saka id referenced (ing siji utawa loro sisi), utawa koleksi kayadene junction terpisah kanggo data hubungan sing sugih.

## Ngreslusi reference ($lookup)

```js
// join referenced data when needed
db.books.aggregate([
  { $lookup: { from: "authors", localField: "authorId", foreignField: "_id", as: "author" } }
]);
```

## Apa iku penting

Nggawe model hubungan iku dhasar banget ing desain database, lan pendekatan MongoDB sing fleksibel lan disetengahake saka pola akses beda karo foreign key SQL sing seragam, dadi ngerti ake nggawe model hubungan ing MongoDB kuwi penting banget kanggo desain schema sing efektif.

Insight penting yaiku MongoDB nggawe model hubungan nganggo **embedding utawa referencing** adhedhasar karakteristik hubungan — lan ngerti **ake cardinality ngaruhi pilihan** kuwi skill penting: **one-to-one** (biasane embed — disinaoko bebarengan), **one-to-many** karo nuansa penting (**one-to-few** → embed kanggo data bounded sing disinaoko bebarengan; **one-to-many** → reference saka sisi many; **one-to-squillions** → tansah reference, aja embed data tandhes wates amarga wates dokumen 16MB lan performa), lan **many-to-many** (array saka id referenced, utawa koleksi kayadene junction).

Pengambilan keputusan dhasar cardinality iki (utamane nggengi ake kapan data kuwi gedhe/tandhes wates supaya aja embed) kuwi penting kanggo ngindhari kesalahan umum kayadene embed array tandhes wates (gedhe dokumen, jempe wates) utawa referencing berlebihan kanggo data sing kudune embed.

Ngerti ake **ngreslusi reference** karo `$lookup` nalika join dibutuhake kuwi ngrampungi gambaran.

Amarga hubungan antarane entitas kuwi melekat ing paling akeh model data, lan amarga pendekatan MongoDB sing fleksibel kanggo saben hubungan (embed versus reference adhedhasar cardinality lan pola akses) kuwi beda landhanan lan luwih rumit tinimbang foreign key SQL sing seragam, ngerti ake nggawe model hubungan ing MongoDB — pilihan embed/reference dhasar cardinality (utamane bedane one-to-few/many/squillions) lan ngreslusi reference — kuwi ilmu sing penting lan asring dienggo kanggo desain schema MongoDB sing efektif, ngbangun embedding dhasar/ngreferensi kanggo tangani hubungan sing ana ing saben aplikasi nyata, lan area penting sing bisa bedain MongoDB modeling sing bener saka port relational sing naif.