如何从一个集合引用另一个集合的数据? Mongodb [英] How can I get data referencing form one collection to another? Mongodb

问题描述

router.get('/productSelect', (req, res, next) =>{
    productSchema.aggregate([   
        { $lookup:
            {
                from: 'supplierSchema',
                localField: 'supplierId',
                foreignField: '_id',
                as: 'supplier'
            }
        }

    ], (err, productSchema) =>{
        if(err) res.json(err);
        else res.json(productSchema);
    });
});

我想从集合中获取数据

[
  {
    "_id": "5ba26ff33318b51e20a80fb3",
    "productExist": true,
    "productName": "Anything",
    "supplierId": "5b9d25064dcf2327b449ae1b",
    "brandId": "5b9d162a316e8d2660f26393",
    "categoryId": "5ba2509a6367372568b1ce6d",
    "productPrice": 222,
    "productQuantity": 320,
    "productMax": 3,
    "productMin": 4,
    "productTimeStamp": "2018-09-19T15:49:07.177Z",
    "__v": 0
  }
]

并从集合中将SupplierId替换为SupplierName

and replace the supplierId as supplierName from collection

[
  {
    "_id": "5b9d25064dcf2327b449ae1b",
    "supplierExist": true,
    "supplierName": "NBA World Wide",
    "supplierStatus": "Available",
    "supplierTimeStamp": "2018-09-15T15:28:06.971Z",
    "__v": 0
  }
]

推荐答案

要与两个表联接，必须确保两个字段(即localField和foriegnField)的类型都相同.

For making join with two table you have make sure that the type for both the fields i.e. localField and foriegnField should be the same.

或

使用mongodb 4.0 ，您可以使用 $toObjectId 聚合

With mongodb 4.0 you can easily change the type of the String to ObjectId using $toObjectId aggregation

productSchema.aggregate([   
  { "$lookup": {
    "from": "supplierSchema",
    "let": { "supplierId": { "$toObjectId": "$supplierId" }},
    "pipeline": [
      { "$match": { "$expr": { "$eq": ["$_id", "$$supplierId"] }}}
    ]
    as: "supplier"
  }}
])

这篇关于如何从一个集合引用另一个集合的数据? Mongodb的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！