我在兩個 MongoDB 集合中有如下資料。類別：
[
{ "_id" : 1, "name" : "A" },
{ "_id" : 2, "name" : "B", "categoryId" : 1 },
{ "_id" : 3, "name" : "C", "categoryId" : 1 },
{ "_id" : 4, "name" : "D", "categoryId" : 2 },
{ "_id" : 5, "name" : "E", "categoryId" : 3 },
{ "_id" : 6, "name" : "F", "categoryId" : 2 }
];
我有Locos檔案：
[
{ "_id" : 1, "name" : "X", "categoryId" : 2 },
{ "_id" : 2, "name" : "Y", "categoryId" : 3 },
{ "_id" : 2, "name" : "B", "categoryId" : 1 }
]
例如，如果我想獲取所有具有 id 1的類別A的孩子，我呼叫該函式，它回傳一個孩子類別的 id 陣列，如果可能的話，回傳 Locos 孩子。所以結果會是這樣的：
chilren: {
categories: [2, 3, 4, 5, 6],
locos: [1, 2, 3]
}
如果我使用 id 2即類別B呼叫函式，我會得到結果：
chilren: {
categories: [2, 6],
locos: [1]
}
uj5u.com熱心網友回復：
您在正確的軌道上使用$graphLookup.
db.categories.aggregate([
{
"$match": {
_id: 1
}
},
{
"$graphLookup": {
"from": "categories",
"startWith": "$_id",
"connectFromField": "_id",
"connectToField": "categoryId",
"as": "categoryLookup"
}
},
{
"$graphLookup": {
"from": "locos",
"startWith": "$_id",
"connectFromField": "_id",
"connectToField": "categoryId",
"as": "locosLookup"
}
},
{
"$project": {
children: {
categories: {
"$map": {
"input": "$categoryLookup",
"as": "c",
"in": "$$c._id"
}
},
locos: {
"$map": {
"input": "$locosLookup",
"as": "l",
"in": "$$l._id"
}
}
}
}
}
])
這是Mongo游樂場供您參考。
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