MongoDB trois collections globales

Question

Learning MongoDB pour les deux derniers jours et je suis en train de regrouper trois collections, mais incapables de réaliser

Voici la collection de quatre maintenir dans la base de données

université

{ 
    "_id" : "5834ecf7432d92675bde9d82", 
    "name": "NIFT" 
} 

collège

{ 
    "_id" : "5834ecf7432d92675bde9d83", 
    "name": "NIFT Hyderabad", 
    "university_id":"5834ecf7432d92675bde9d82" 
} 

départements

{ 
    "_id" : "5834ecf7432d92675bde9d84", 
    "department_name": "Fashion Technology", 
    "college_id" : "5834ecf7432d92675bde9d83" 
}, 
{ 
    "_id" : "5834ecf7432d92675bde9d85", 
    "department_name": "Merchandising", 
    "college_id" : "5834ecf7432d92675bde9d83" 
} 

Sections

{ 
    "_id" : "5834ecf7432d92675bde9d86", 
    "section_name": "A", 
    "students" : "56", 
    "department_id":"5834ecf7432d92675bde9d84" 
}, 
{ 
    "_id" : "5834ecf7432d92675bde9d87", 
    "section_name": "B", 
    "students" : "60", 
    "department_id":"5834ecf7432d92675bde9d84" 
}, 
{ 
    "_id" : "5834ecf7432d92675bde9d86", 
    "section_name": "A", 
    "students" : "55", 
    "department_id":"5834ecf7432d92675bde9d85" 
}, 
{ 
    "_id" : "5834ecf7432d92675bde9d87", 
    "section_name": "B", 
    "students" : "44", 
    "department_id":"5834ecf7432d92675bde9d85" 
} 

Ici, je suis en train d'atteindre la sortie dans le format ci-dessous

de sortie prévue

[{ 
    "_id": "5834ecf7432d92675bde9d83", 
    "name": "NIFT Hyderabad", 
    "university_id": "5834ecf7432d92675bde9d82", 
    "departments": [{ 
     "_id": "5834ecf7432d92675bde9d84", 
     "department_name": "CSE", 
     "college_id": "5834ecf7432d92675bde9d83", 
     "sections": [{ 
      "_id": "5834ecf7432d92675bde9d86", 
      "section_name": "A", 
      "students": "56", 
      "department_id": "5834ecf7432d92675bde9d84" 
     }, { 
      "_id": "5834ecf7432d92675bde9d87", 
      "section_name": "B", 
      "students": "60", 
      "department_id": "5834ecf7432d92675bde9d84" 
     }] 
    }, 
    { 
     "_id": "5834ecf7432d92675bde9d85", 
     "department_name": "Mechanical", 
     "college_id": "5834ecf7432d92675bde9d83", 
     "sections": [{ 
       "_id": "5834ecf7432d92675bde9d86", 
       "section_name": "A", 
       "students": "55", 
       "department_id": "5834ecf7432d92675bde9d85" 
      }, 
      { 
       "_id": "5834ecf7432d92675bde9d87", 
       "section_name": "B", 
       "students": "44", 
       "department_id": "5834ecf7432d92675bde9d85" 
      } 
     ] 
    } 
    ] 
}] 

Mais, je reçois département et sections dans des réseaux séparés pour le collège, mais pas en mesure d'obtenir comme dans le format ci-dessus

Recherche

db.college.aggregate([ 
      {"$match": { "university_id": "5834ecf7432d92675bde9d82" } }, 
      {"$lookup": { 
      "localField": "_id", 
      "from": "departments", 
      "foreignField": "college_id", 
      "as": "departments" 
     }}, 
     {"$unwind":"$departments"}, 
     {$group : {_id : "$_id", departments : {$push : "$departments" }}}, 
     {"$lookup": { 
     "localField": "departments._id", 
     "from": "sections", 
     "foreignField": "department_id", 
     "as": "sections"} 
     } 
     ]) 

Quelqu'un peut-il me aider à résoudre ce question, ce sera très utile pour moi.

Answer 1

Vous pouvez essayer la requête d'agrégation ci-dessous.

La requête ci-dessous pousse le sections en department lorsqu'ils sont joints et $group pour pousser le département à créer la structure finale.

db.college.aggregate([ 
    { 
    "$match": { 
     "university_id": "5834ecf7432d92675bde9d82" 
    } 
    }, 
    { 
    "$lookup": { 
     "localField": "_id", 
     "from": "departments", 
     "foreignField": "college_id", 
     "as": "departments" 
    } 
    }, 
    { 
    "$unwind": { 
    "path": "$departments", 
    "preserveNullAndEmptyArrays": true 
    } 
    }, 
    { 
    "$lookup": { 
     "localField": "departments._id", 
     "from": "sections", 
     "foreignField": "department_id", 
     "as": "departments.sections" 
    } 
    }, 
    { 
    "$group": { 
     "_id": "$_id", 
     "name": { 
     "$first": "$name" 
     }, 
     "university_id": { 
     "$first": "$university_id" 
     }, 
     "departments": { 
     "$push": "$departments" 
     } 
    } 
    } 
])