Apa iku aggregation pipeline?

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Accepted Answer

The **aggregation pipeline** adalah kerangka kerja MongoDB sing kuwat kanggo **processing data lan analysis** — iku ngirim dokumen liwat urutan **stages**, saben-sabene ngowah data (filtering, grouping, computing). Iku padha karo SQL's GROUP BY lan query analitik sing rumit, nanging luwih fleksibel.

## Konsep pipeline: stages ngowah data

```js
db.orders.aggregate([
  { $match: { status: "completed" } },          // 1. FILTER (like WHERE)
  { $group: {                                    // 2. GROUP and aggregate
      _id: "$customerId",                         //    group by customerId
      total: { $sum: "$amount" },                 //    sum amounts per customer
      count: { $sum: 1 }                          //    count orders
  }},
  { $sort: { total: -1 } },                       // 3. SORT by total
  { $limit: 10 }                                  // 4. top 10
]);
// documents flow through each stage; each stage's output feeds the next
```

Dokumen mili liwat stages kanthi urutan — saben stage ngowah lan ngirim hasil menyang sing sabanjure. Pipeline iki ngetung total per-customer, disusun, top 10 — kaya query SQL GROUP BY.

## Common pipeline stages

```text
$match    → filter documents (like WHERE) — put EARLY to reduce data
$group    → group by a key and aggregate ($sum, $avg, $max, $min, $push, etc.)
$sort     → order documents
$project  → reshape documents (include/exclude/compute fields)
$limit / $skip → pagination
$unwind   → deconstruct an array field into multiple documents (one per element)
$lookup   → JOIN with another collection
$addFields → add computed fields
$count    → count documents
```

## $lookup — gabung collections

```js
// $lookup performs a left-outer JOIN to another collection
db.orders.aggregate([
  { $lookup: {
      from: "customers",
      localField: "customerId",
      foreignField: "_id",
      as: "customer"           // joined customer data added as an array field
  }}
]);
```

`$lookup` ngaktifake joins (sing MongoDB umumé ireng liwat embedding) — berguna nalika sampeyan kudu gabung collections.

## $unwind — ekspansi array

```js
// turn one document with an array into multiple documents (one per array element)
db.posts.aggregate([
  { $unwind: "$tags" },                           // one doc per tag
  { $group: { _id: "$tags", count: { $sum: 1 } } } // count posts per tag
]);
```

## Kenapa iki penting

The aggregation pipeline iku salah sawijining fitur MongoDB sing paling kuwat lan penting — iku piranti utama kanggo **data analysis, reporting, lan transformasi sing rumit**, dadi ngerti iku kudu kanggo pekerjaan MongoDB sing serius sabanjure basic queries.

The pipeline's **stage-based model** (dokumen mili liwat sequential transformation stages, saben filtering, grouping, reshaping, utawa computing) iku konsep sing elegan lan ngaktifake processing data sing sophisticated sing simple `find` queries ora iso — iku padha karo SQL's GROUP BY lan analytical queries, nanging luwih fleksibel lan composable.

Ngerti stages sing umum — **`$match`** (filtering, ideally awal kanggo ngurangi data), **`$group`** (grouping lan aggregating karo `$sum`, `$avg`, etc. — inti dari analytics), **`$sort`/`$limit`** (ordering lan pagination), **`$project`** (reshape dokumen), **`$unwind`** (ekspansi array menyang dokumen — penting kanggo analisis data array, umum ing MongoDB), lan **`$lookup`** (gabung collections — ngaktifake joins sing MongoDB umumé ireng) — nyakup toolkit kanggo processing data sing nyata.

The pipeline nangani reporting, analytics, transformasi data, lan query sing rumit (aggregations, joins, array processing) sing umum butuh ing aplikasi.

Amarga data analysis lan querying sing rumit iku butuh penting kanggo database apa apa, lan amarga aggregation pipeline iku piranti MongoDB sing kuwat lan fleksibel (nglampui CRUD basic), ngerti aggregation pipeline — stage model lan key stages ($match, $group, $sort, $project, $unwind, $lookup) — iku pengetahuan MongoDB sing kudu lan sering diterapake kanggo analytics, reporting, lan transformasi data sing rumit, ciri-ciri MongoDB skill advanced lan salah sawijining topik MongoDB sing paling penting kanggo nglumpuke analytical value saka database.