Piye cara kerja query find lan projection?

Question

Accepted Answer

Metode **`find`** ngambil dokumen sing cocok karo filter; **projection** ngontrol field mana sing dibalekake. Bareng-bareng, mula luwih gampang nggarap untuk nggoleki dokumen sing tepat lan mbentuk output — dhasar penting kanggo maca data kanthi efisien.

## find — query dokumen

```js
db.users.find();                          // all documents
db.users.find({ age: { $gt: 25 } });      // filter: matching documents (a CURSOR)
db.users.findOne({ email: "ann@x.com" }); // the FIRST matching document (or null)

// find returns a CURSOR you can chain methods on
db.users.find({ active: true })
  .sort({ name: 1 })                      // sort
  .limit(10)                              // limit
  .skip(20);                              // skip (pagination)
```

`find` ngembalikan **cursor** (pointer menyang hasil) sing bisa digawe chain karo `sort`, `limit`, `skip`, lan liyane. `findOne` ngembalikan siji dokumen langsung.

## Projection — pilih field mana sing dibalekake

```js
// projection: 1 = include, 0 = exclude
db.users.find({ active: true }, { name: 1, email: 1 });        // only name and email (+ _id)
db.users.find({}, { password: 0 });                           // everything EXCEPT password
db.users.find({}, { name: 1, _id: 0 });                       // name only, exclude _id
```

**Projection** (argumen kapindho) ngontrol field sing dibalekake: `1` nglebokake, `0` mbuang. `_id` dilebok kanthi bawaan (buwang karo `_id: 0`). Sampeyan umume ora bisa nyinauni include lan exclude (kejaba kanggo `_id`).

## Napa projection penting: efisiensi lan keamanan

```text
✓ EFFICIENCY — return only needed fields → less data transferred (especially for large
  documents or large result sets) → faster
✓ SECURITY — EXCLUDE sensitive fields (passwords, internal data) so they don't leak
  → e.g. always project out password fields when returning user data
```

## Projection field nested lan array

```js
db.users.find({}, { "address.city": 1 });        // nested field (dot notation)
db.posts.find({}, { comments: { $slice: 5 } });   // first 5 array elements
```

## Napa iki penting

`find` lan projection dhasar kanggo **maca data** ing MongoDB — nggarap nggoleki dokumen sing tepat lan mbentuk output minangka kabutuhan sing tetep, dadi ngerti bab iki dhasar ilmu sing penting saben dina.

Nerangake carane `find` gumana (ngembalikan cursor saka dokumen sing cocok, bisa digawe chain karo `sort`/`limit`/`skip` kanggo urutan lan pagination) lan `findOne` (siji dokumen) iku dhasar kanggo maca data. **Projection** utamane penting duwe loro alesan praktis: **efisiensi** (ngembalikan mung field sing perlokale nyuda data sing dikirim — penting kanggo dokumen gedhe utawa hasil sing akeh, nambah performa) lan utamane **keamanan** (menggak field sensitif kayata password utawa data internal supaya ora bocor ing asil query — praktik umum sing penting, contone mesthi buwang field password nalika balekake data user, padha karo nggunakake response models ing APIs).

Nerangake carane nglebokake (`1`) utawa mbuang (`0`) field, yen `_id` dilebok kanthi bawaan, lan carane projection nested/array fields nutupi pembentukan praktis asil query.

Karena maca data minangka operasi database sing paling sering, lan karena `find` karo projection carane ngambil dokumen sing tepat kanthi efisien lan aman karo field sing tepat, nerangake find queries lan projections — model cursor, chain kanggo sort/pagination, lan utamane projection kanggo efisiensi lan keamanan (menggak data sensitif) — ilmu MongoDB sing penting, sering ditrapake kanggo kode reading data apa wae, karo aspek keamanan proyeksine menggak field sensitif minangka pertimbangan praktis sing utama.