MongoDB $reverseArray

Di MongoDB, $reverseArray operator pipa agregasi membalikkan urutan item dalam array.

Ia menerima ekspresi array sebagai argumen dan mengembalikan array dengan elemen dalam urutan terbalik.

Contoh

Misalkan kita memiliki koleksi yang disebut products dengan dokumen sebagai berikut:

{ "_id" : 1, "prod" : "Bat", "sizes" : [ "S", "M", "L" ] }
{ "_id" : 2, "prod" : "Hat", "sizes" : [ "XS", "S", "L", "XL" ] }
{ "_id" : 3, "prod" : "Cap", "sizes" : [ "M", "L" ] }

Kita dapat menggunakan $reverseArray operator untuk membalik urutan elemen array tersebut.

Contoh:

db.products.aggregate(
   [
     { $match: { _id: { $in: [ 1, 2, 3 ] } } },
     {
       $project:
          {
            _id: 0,
            sizes: 1,
            reversed: { $reverseArray: [ "$sizes" ] }
          }
     }
   ]
)

Hasil:

{ "sizes" : [ "S", "M", "L" ], "reversed" : [ "L", "M", "S" ] }
{ "sizes" : [ "XS", "S", "L", "XL" ], "reversed" : [ "XL", "L", "S", "XS" ] }
{ "sizes" : [ "M", "L" ], "reversed" : [ "L", "M" ] }

Array Kosong

Melewati array kosong akan mengembalikan array kosong.

Contoh dokumen:

{ "_id" : 4, "prod" : "Zap", "sizes" : [ ] }

Terapkan $reverseArray :

db.products.aggregate(
   [
     { $match: { _id: { $in: [ 4 ] } } },
     {
       $project:
          {
            _id: 0,
            sizes: 1,
            reversed: { $reverseArray: [ "$sizes" ] }
          }
     }
   ]
)

Hasil:

{ "sizes" : [ ], "reversed" : [ ] }

Nilai Null

Melewati nilai null mengembalikan null .

Contoh dokumen:

{ "_id" : 5, "prod" : "Tap", "sizes" : null }

Terapkan $reverseArray :

db.products.aggregate(
   [
     { $match: { _id: { $in: [ 5 ] } } },
     {
       $project:
          {
            _id: 0,
            sizes: 1,
            reversed: { $reverseArray: [ "$sizes" ] }
          }
     }
   ]
)

Hasil:

{ "sizes" : null, "reversed" : null }

Bidang Tidak Ada

Menerapkan $reverseArray ke bidang yang tidak ada di dokumen menghasilkan null dikembalikan.

Contoh dokumen:

{ "_id" : 6, "prod" : "Map" }

Terapkan $reverseArray :

db.products.aggregate(
   [
     { $match: { _id: { $in: [ 6 ] } } },
     {
       $project:
          {
            _id: 0,
            sizes: 1,
            reversed: { $reverseArray: [ "$sizes" ] }
          }
     }
   ]
)

Hasil:

{ "reversed" : null }

Jenis Data Salah

Menerapkan $reverseArray ke bidang yang tidak diselesaikan ke larik menghasilkan kesalahan.

Contoh dokumen:

{ "_id" : 7, "prod" : "Box", "sizes" : "XXL" }

Terapkan $reverseArray :

db.products.aggregate(
   [
     { $match: { _id: { $in: [ 7 ] } } },
     {
       $project:
          {
            _id: 0,
            sizes: 1,
            reversed: { $reverseArray: [ "$sizes" ] }
          }
     }
   ]
)

Hasil:

uncaught exception: Error: command failed: {
	"ok" : 0,
	"errmsg" : "The argument to $reverseArray must be an array, but was of type: string",
	"code" : 34435,
	"codeName" : "Location34435"
} : aggregate failed :
[email protected]/mongo/shell/utils.js:25:13
[email protected]/mongo/shell/assert.js:18:14
[email protected]/mongo/shell/assert.js:639:17
[email protected]/mongo/shell/assert.js:729:16
[email protected]/mongo/shell/db.js:266:5
[email protected]/mongo/shell/collection.js:1058:12
@(shell):1:1