C'était délicat pour quelqu'un qui ne connaissait pas MongoDb aggregate de . Je vais décomposer ma réponse en étapes pour montrer à d'autres qui tentent d'agréger un tableau en référençant plusieurs collections.
Étape 1 : $match pour filtrer la collecte
Le $match accepte les mêmes requêtes que db.collection.find({}) et renvoie un tableau de résultats correspondants dans le cas ci-dessous, je sélectionne 4 enregistrements spécifiques ici
{ '$match':
{ _id:
{ '$in':
[
ObjectId('5f7bdb3eea134b5a5c976285'),
ObjectId('5f7bdb3eea134b5a5c976283'),
ObjectId('5f7bdb3eea134b5a5c976284'),
ObjectId('5f7bdb3eea134b5a5c976289')
]
}
}
}
[
{ _id: ObjectId('5f7be0b37e2bdf5b19e4724d'),
name: 'CAPTAIN_SAIL',
classes: [ 'sail' ],
license: 'WC-1',
watercraftContexts:
[ { _id: ObjectId('5f7be0b37e2bdf5b19e47241'),
watercraftType: 'Sailboat',
ref: 'sailboats' } ],
__v: 0 },
{ _id: ObjectId('5f7be0b37e2bdf5b19e4724e'),
name: 'CAPTAIN_YATCH',
classes: [ 'yatch' ],
license: 'WC-2',
watercraftContexts:
[ { _id: ObjectId('5f7be0b37e2bdf5b19e47242'),
watercraftType: 'Yatch',
ref: 'yatches' } ],
__v: 0 },
{ _id: ObjectId('5f7be0b37e2bdf5b19e4724f'),
name: 'CAPTAIN_SHIP',
classes: [ 'ship' ],
license: 'WC-3',
watercraftContexts:
[ { _id: ObjectId('5f7be0b37e2bdf5b19e47243'),
watercraftType: 'Ship',
ref: 'ships' } ],
__v: 0 },
{ _id: ObjectId('5f7be0b37e2bdf5b19e47253'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
[ { _id: ObjectId('5f7be0b37e2bdf5b19e4724a'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
{ _id: ObjectId('5f7be0b37e2bdf5b19e4724b'),
watercraftType: 'Yatch',
ref: 'yatches' },
{ _id: ObjectId('5f7be0b37e2bdf5b19e4724c'),
watercraftType: 'Ship',
ref: 'ships' } ],
__v: 0 }
]
Étape 2 - $unwind afin que nous puissions itérer avec $loopup
Dans cet ensemble de résultats, il existe un tableau d'objets avec { _id: <ObjectId>, watercraftType: <ModelName> } pour boucler sur le tableau et joindre chacun de ces objets avec leur enregistrement de collection respectif, nous devons diviser le tableau en enregistrements individuels indépendants. Le $unwind la fonctionnalité créera un nouvel ensemble de données pour la prochaine étape agrégée
{ '$unwind': '$watercraftContexts' },
Comme vous pouvez le voir, $unwind crée maintenant un enregistrement avec un seul watercraftContext nous sommes maintenant prêts à utiliser le $lookup
[ { _id: ObjectId('5f7be2231da37c5b5915bf9b'),
name: 'CAPTAIN_SAIL',
classes: [ 'sail' ],
license: 'WC-1',
watercraftContexts:
{ _id: ObjectId('5f7be2231da37c5b5915bf8f'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0 },
{ _id: ObjectId('5f7be2231da37c5b5915bf9c'),
name: 'CAPTAIN_YATCH',
classes: [ 'yatch' ],
license: 'WC-2',
watercraftContexts:
{ _id: ObjectId('5f7be2231da37c5b5915bf90'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0 },
{ _id: ObjectId('5f7be2231da37c5b5915bf9d'),
name: 'CAPTAIN_SHIP',
classes: [ 'ship' ],
license: 'WC-3',
watercraftContexts:
{ _id: ObjectId('5f7be2231da37c5b5915bf91'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0 },
{ _id: ObjectId('5f7be2231da37c5b5915bfa1'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7be2231da37c5b5915bf98'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0 },
{ _id: ObjectId('5f7be2231da37c5b5915bfa1'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7be2231da37c5b5915bf99'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0 },
{ _id: ObjectId('5f7be2231da37c5b5915bfa1'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7be2231da37c5b5915bf9a'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0 } ]
Il est important de noter que nous devons $unwind avant d'appeler $lookup pour chaque collection différente que nous devons rejoindre. Puisque nous voulons joindre plusieurs collections, nous devons stocker le résultat dans un objet indexé par la collection pour une agrégation ultérieure.
// Only performs $lookup on 'ships' collection
{ '$lookup':
{ from: 'ships', // Collection Name - Note: repeat for each collection
localField: 'watercraftContexts._id', // The field with id to link
foreignField: '_id', // The field on the foreign collection to match
as: 'watercrafts.ships' // The path where to store the lookup result
}
}
Étape 5 - Répétez $unwind et $lookup pour les autres jointures
Répétez les étapes ci-dessus pour les jointures supplémentaires et entrez le nom de la collection. J'ai combiné les étapes agrégées pour démontrer la répétition.
{ '$unwind': '$watercraftContexts' },
{ '$lookup':
{ from: 'yatches',
localField: 'watercraftContexts._id',
foreignField: '_id',
as: 'watercrafts.yatches' } },
{ '$unwind': '$watercraftContexts' },
{ '$lookup':
{ from: 'sailboats',
localField: 'watercraftContexts._id',
foreignField: '_id',
as: 'watercrafts.sailboats' } }
Si vous regardez attentivement, vous remarquez que l'un des Captain les enregistrements existent 3 fois avec un watercraftType différent . $lookup renverra uniquement les enregistrements correspondant à un nom de collection spécifique. C'est pourquoi pourquoi les stocker dans un Object saisi par collectionName
[
{ _id: ObjectId('5f7be7145320a65b942bb450'),
name: 'CAPTAIN_SAIL',
classes: [ 'sail' ],
license: 'WC-1',
watercraftContexts:
{ _id: ObjectId('5f7be7145320a65b942bb444'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0,
watercrafts:
{ ships: [],
yatches: [],
sailboats:
[ { _id: ObjectId('5f7be7145320a65b942bb444'),
class: 'sail',
name: 'Gone with the Wind',
__v: 0 } ] } },
{ _id: ObjectId('5f7be7145320a65b942bb451'),
name: 'CAPTAIN_YATCH',
classes: [ 'yatch' ],
license: 'WC-2',
watercraftContexts:
{ _id: ObjectId('5f7be7145320a65b942bb445'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0,
watercrafts:
{ ships: [],
yatches:
[ { _id: ObjectId('5f7be7145320a65b942bb445'),
class: 'yatch',
name: 'Liquid Gold',
__v: 0 } ],
sailboats: [] } },
{ _id: ObjectId('5f7be7145320a65b942bb452'),
name: 'CAPTAIN_SHIP',
classes: [ 'ship' ],
license: 'WC-3',
watercraftContexts:
{ _id: ObjectId('5f7be7145320a65b942bb446'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0,
watercrafts:
{ ships:
[ { _id: ObjectId('5f7be7145320a65b942bb446'),
class: 'ship',
name: 'Jenny',
__v: 0 } ],
yatches: [],
sailboats: [] } },
{ _id: ObjectId('5f7be7145320a65b942bb456'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7be7145320a65b942bb44d'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0,
watercrafts:
{ ships: [],
yatches: [],
sailboats:
[ { _id: ObjectId('5f7be7145320a65b942bb44d'),
class: 'sail',
name: 'Swell Shredder',
__v: 0 } ] } },
{ _id: ObjectId('5f7be7145320a65b942bb456'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7be7145320a65b942bb44e'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0,
watercrafts:
{ ships: [],
yatches:
[ { _id: ObjectId('5f7be7145320a65b942bb44e'),
class: 'yatch',
name: 'Audrey',
__v: 0 } ],
sailboats: [] } },
{ _id: ObjectId('5f7be7145320a65b942bb456'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7be7145320a65b942bb44f'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0,
watercrafts:
{ ships:
[ { _id: ObjectId('5f7be7145320a65b942bb44f'),
class: 'ship',
name: 'Jenny IV',
__v: 0 } ],
yatches: [],
sailboats: [] } } ]
Étape 6 $project - Utilisez project pour aplatir la carte d'objets des jointures
Nous pouvons utiliser le projet pour sélectionner toutes les données existantes et aplatir la carte d'objets des résultats de jointure en un seul tableau.
{ '$project':
// keys with the value 'true' will be included
{ name: true,
license: true,
classes: true,
_id: true,
watercraftContexts: true,
__v: true,
watercrafts: // Re-assigns value of watercrafts
{ '$setUnion': // Accepts an array of arrays to flatten
[
'$watercrafts.ships',
'$watercrafts.yatches',
'$watercrafts.sailboats'
]
}
}
}
Les résultats du $project ci-dessus remplacera les watercrafts objet avec un tableau aplati de watercrafts , mais il est important de noter qu'il existe encore des enregistrements en double de Captain où la correspondance de nombreuses recherches différentes. Nous les reconstituerons à l'étape suivante.
[ { _id: ObjectId('5f7bea8d79dfe25bf3cb9695'),
name: 'CAPTAIN_SAIL',
classes: [ 'sail' ],
license: 'WC-1',
watercraftContexts:
{ _id: ObjectId('5f7bea8d79dfe25bf3cb9689'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0,
watercrafts:
[ { _id: ObjectId('5f7bea8d79dfe25bf3cb9689'),
class: 'sail',
name: 'Gone with the Wind',
__v: 0 } ] },
{ _id: ObjectId('5f7bea8d79dfe25bf3cb9696'),
name: 'CAPTAIN_YATCH',
classes: [ 'yatch' ],
license: 'WC-2',
watercraftContexts:
{ _id: ObjectId('5f7bea8d79dfe25bf3cb968a'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0,
watercrafts:
[ { _id: ObjectId('5f7bea8d79dfe25bf3cb968a'),
class: 'yatch',
name: 'Liquid Gold',
__v: 0 } ] },
{ _id: ObjectId('5f7bea8d79dfe25bf3cb9697'),
name: 'CAPTAIN_SHIP',
classes: [ 'ship' ],
license: 'WC-3',
watercraftContexts:
{ _id: ObjectId('5f7bea8d79dfe25bf3cb968b'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0,
watercrafts:
[ { _id: ObjectId('5f7bea8d79dfe25bf3cb968b'),
class: 'ship',
name: 'Jenny',
__v: 0 } ] },
{ _id: ObjectId('5f7bea8d79dfe25bf3cb969b'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7bea8d79dfe25bf3cb9692'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0,
watercrafts:
[ { _id: ObjectId('5f7bea8d79dfe25bf3cb9692'),
class: 'sail',
name: 'Swell Shredder',
__v: 0 } ] },
{ _id: ObjectId('5f7bea8d79dfe25bf3cb969b'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7bea8d79dfe25bf3cb9693'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0,
watercrafts:
[ { _id: ObjectId('5f7bea8d79dfe25bf3cb9693'),
class: 'yatch',
name: 'Audrey',
__v: 0 } ] },
{ _id: ObjectId('5f7bea8d79dfe25bf3cb969b'),
name: 'CAPTAIN_SAIL_YATCH_SHIP',
classes: [ 'sail', 'yatch', 'ship' ],
license: 'WC-7',
watercraftContexts:
{ _id: ObjectId('5f7bea8d79dfe25bf3cb9694'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0,
watercrafts:
[ { _id: ObjectId('5f7bea8d79dfe25bf3cb9694'),
class: 'ship',
name: 'Jenny IV',
__v: 0 } ] } ]
Étape 7 $dérouler et $grouper
Nous $unwind afin que nous puissions maintenant regrouper tous les watercrafts appartenant au même Captain . Nous devons également utiliser $mergeObjects pour stocker temporairement les données supplémentaires du Captain collecte sous une nouvelle variable temporaire pour préparer les étapes finales.
{ '$unwind': '$watercrafts' },
{ '$group':
{ _id: '$_id',
data:
{ '$mergeObjects':
{ name: '$name',
license: '$license',
classes: '$classes',
watercraftContexts: '$watercraftContexts',
__v: '$__v' } },
watercrafts: { '$push': '$watercrafts' } } }
$unwind et $group Résultat
Maintenant, nous allons vraiment quelque part. Nous avons réduit notre transformation à nos 4 premiers Captain s et aplati nos jointures en un seul tableau.
[ { _id: ObjectId('5f7bed5e271dd95c306c25a4'),
data:
{ name: 'CAPTAIN_SHIP',
license: 'WC-3',
classes: [ 'ship' ],
watercraftContexts:
{ _id: ObjectId('5f7bed5e271dd95c306c2598'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0 },
watercrafts:
[ { _id: ObjectId('5f7bed5e271dd95c306c2598'),
class: 'ship',
name: 'Jenny',
__v: 0 } ] },
{ _id: ObjectId('5f7bed5e271dd95c306c25a8'),
data:
{ name: 'CAPTAIN_SAIL_YATCH_SHIP',
license: 'WC-7',
classes: [ 'sail', 'yatch', 'ship' ],
watercraftContexts:
{ _id: ObjectId('5f7bed5e271dd95c306c25a1'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0 },
watercrafts:
[ { _id: ObjectId('5f7bed5e271dd95c306c259f'),
class: 'sail',
name: 'Swell Shredder',
__v: 0 },
{ _id: ObjectId('5f7bed5e271dd95c306c25a0'),
class: 'yatch',
name: 'Audrey',
__v: 0 },
{ _id: ObjectId('5f7bed5e271dd95c306c25a1'),
class: 'ship',
name: 'Jenny IV',
__v: 0 } ] },
{ _id: ObjectId('5f7bed5e271dd95c306c25a2'),
data:
{ name: 'CAPTAIN_SAIL',
license: 'WC-1',
classes: [ 'sail' ],
watercraftContexts:
{ _id: Object('5f7bed5e271dd95c306c2596'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0 },
watercrafts:
[ { _id: ObjectId('5f7bed5e271dd95c306c2596'),
class: 'sail',
name: 'Gone with the Wind',
__v: 0 } ] },
{ _id: ObjectId('5f7bed5e271dd95c306c25a3'),
data:
{ name: 'CAPTAIN_YATCH',
license: 'WC-2',
classes: [ 'yatch' ],
watercraftContexts:
{ _id: ObjectId('5f7bed5e271dd95c306c2597'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0 },
watercrafts:
[ { _id: ObjectId('5f7bed5e271dd95c306c2597'),
class: 'yatch',
name: 'Liquid Gold',
__v: 0 } ] } ]
Étape 8 $replaceRoot et $project
Il ne nous reste plus qu'à fusionner nos data à la racine de chaque enregistrement et supprimez la variable temporaire data
// Merges 'data' into the root of each record
{ '$replaceRoot': { newRoot: { '$mergeObjects': [ '$data', '$$ROOT' ] } } },
// Use $project to remove data (include only the fields we want)
{ '$project':
{ name: true,
license: true,
classes: true,
_id: true,
watercraftContexts: true,
__v: true,
watercrafts: true }
}
Nous avons maintenant le résultat que nous avons prévu pour... Un Captain avec un tableau de types mixtes associés watercrafts
[
{ name: 'CAPTAIN_SAIL_YATCH_SHIP',
license: 'WC-7',
classes: [ 'sail', 'yatch', 'ship' ],
watercraftContexts:
{ _id: ObjectId('5f7bf3b3680b375ca1755ea6'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0,
_id: ObjectId('5f7bf3b3680b375ca1755ead'),
watercrafts:
[ { _id: ObjectId('5f7bf3b3680b375ca1755ea4'),
class: 'sail',
name: 'Swell Shredder',
__v: 0 },
{ _id: ObjectId('5f7bf3b3680b375ca1755ea5'),
class: 'yatch',
name: 'Audrey',
__v: 0 },
{ _id: ObjectId('5f7bf3b3680b375ca1755ea6'),
class: 'ship',
name: 'Jenny IV',
__v: 0 } ] },
{ name: 'CAPTAIN_SAIL',
license: 'WC-1',
classes: [ 'sail' ],
watercraftContexts:
{ _id: ObjectId('5f7bf3b3680b375ca1755e9b'),
watercraftType: 'Sailboat',
ref: 'sailboats' },
__v: 0,
_id: ObjectId('5f7bf3b3680b375ca1755ea7'),
watercrafts:
[ { _id: ObjectId('5f7bf3b3680b375ca1755e9b'),
class: 'sail',
name: 'Gone with the Wind',
__v: 0 } ] },
{ name: 'CAPTAIN_YATCH',
license: 'WC-2',
classes: [ 'yatch' ],
watercraftContexts:
{ _id: ObjectId('5f7bf3b3680b375ca1755e9c'),
watercraftType: 'Yatch',
ref: 'yatches' },
__v: 0,
_id: ObjectId('5f7bf3b3680b375ca1755ea8'),
watercrafts:
[ { _id: ObjectId('5f7bf3b3680b375ca1755e9c'),
class: 'yatch',
name: 'Liquid Gold',
__v: 0 } ] },
{ name: 'CAPTAIN_SHIP',
license: 'WC-3',
classes: [ 'ship' ],
watercraftContexts:
{ _id: ObjectId('5f7bf3b3680b375ca1755e9d'),
watercraftType: 'Ship',
ref: 'ships' },
__v: 0,
_id: ObjectId('5f7bf3b3680b375ca1755ea9'),
watercrafts:
[ { _id: ObjectId('5f7bf3b3680b375ca1755e9d'),
class: 'ship',
name: 'Jenny',
__v: 0 } ] } ]
Et voilà... il n'a fallu que 2 jours pour comprendre cela. J'espère que cela vous fera gagner du temps si vous essayez une association agrégée similaire. Bon codage !
Projet final
[
{ '$match':
{ _id:
{ '$in':
[ ObjectId('5f7bf3b3680b375ca1755ea9'),
ObjectId('5f7bf3b3680b375ca1755ea7'),
ObjectId('5f7bf3b3680b375ca1755ea8'),
ObjectId('5f7bf3b3680b375ca1755ead')
]
}
}
},
{ '$unwind': '$watercraftContexts' },
{ '$lookup':
{ from: 'ships',
localField: 'watercraftContexts._id',
foreignField: '_id',
as: 'watercrafts.ships' } },
{ '$unwind': '$watercraftContexts' },
{ '$lookup':
{ from: 'yatches',
localField: 'watercraftContexts._id',
foreignField: '_id',
as: 'watercrafts.yatches' } },
{ '$unwind': '$watercraftContexts' },
{ '$lookup':
{ from: 'sailboats',
localField: 'watercraftContexts._id',
foreignField: '_id',
as: 'watercrafts.sailboats' } },
{ '$project':
{ name: true,
license: true,
classes: true,
_id: true,
watercraftContexts: true,
__v: true,
watercrafts:
{ '$setUnion':
[ '$watercrafts.ships',
'$watercrafts.yatches',
'$watercrafts.sailboats' ] } } },
{ '$unwind': '$watercrafts' },
{ '$group':
{ _id: '$_id',
data:
{ '$mergeObjects':
{ name: '$name',
license: '$license',
classes: '$classes',
watercraftContexts: '$watercraftContexts',
__v: '$__v' } },
watercrafts: { '$push': '$watercrafts' } } },
{ '$replaceRoot': { newRoot: { '$mergeObjects': [ '$data', '$$ROOT' ] } } },
{ '$project':
{ name: true,
license: true,
classes: true,
_id: true,
watercraftContexts: true,
__v: true,
watercrafts: true } }
]
