如何从 mongodb 中获取值

Question

开发新手。我正在尝试从 JSON 文件中获取值。有人可以帮我解决这个问题吗？

[{
    "State": "New York",
    "City": "Queens",
    "Cars": {
        "gas": {
            "USAMade": {
                "Ford": ["Fordcars", "Fordtrucks", "Fordsuv"]
            },
            "OutsideUS": {
                "Toyota": ["Tcars", "Ttrucks", "TSUV"]
            }
        },
        "electric": {
            "USAMade": {
                "Tesla": ["model3", "modelS", "modelX"]
            },
            "OutsideUS": {
                "Nissan": ["Ncars", "Ntrucks", "NSUV"]
            }
        }
    }
},
{
    "State": "Atlanta",
    "City": "Roswell",
    "Cars": {
        "gas": {
            "USAMade": {
                "Ford": ["Fordcars", "Fordtrucks", "Fordsuv"]
            },
            "OutsideUS": {
                "Toyota": ["Tcars", "Ttrucks", "TSUV"]
            }
        },
        "electric": {
            "USAMade": {
                "Tesla": ["model3", "modelS", "modelX"]
            },
            "OutsideUS": {
                "Nissan": ["Ncars", "Ntrucks", "NSUV"]
            }
        }
    }
}

]

如何列出汽车类型（gas/electric）？
一旦我得到类型，我想列出各自的制造国家（USAMade/OutsideUS）。
之后我想列出模型 (Ford/Toyota)?

Answer 1

假设您在文件 test.json 中有文档，这里是如何使用 linux shell 工具 cat,jq,sort,uniq:

  1) cat test.json  | jq '.[] | .Cars | keys[] ' | sort | uniq
 "electric"
 "gas"

  2) cat test.json  | jq '.[] | .Cars[] | keys[] ' | sort | uniq
  "OutsideUS"
  "USAMade"

  3) cat test.json  | jq '.[] | .Cars[][] | keys[] ' | sort | uniq
  "Ford"
  "Nissan"
  "Tesla"
  "Toyota"

如果您的数据在 mongoDB 中，我建议您将这个不同的值保存在单独集合中的单个文档中，并在从该集合加载时填充前端页面，文档看起来像这样：

{
State:["Atlanta","Oregon"],
City:["New York" , "Tokio" , "Moskow"],
Location:["OutsideUS" ,"USAMade"],
Model:["Ford","Toyota","Nissan"]
}

您不需要每次加载首页时都从数据库中提取不同的值，因为它不是可扩展的解决方案，并且在某些时候它会成为性能瓶颈...

但是，如果您仍然希望它根据选择仅从 mongoDB 中获取不同的键，您可以执行以下操作：

1.

 mongos> db.test.aggregate([   {"$project":{"akv":{"$objectToArray":"$Cars"}}} ,{$unwind:"$akv"} ,{ $group:{_id:null , "allkeys":{$addToSet:"$akv.k"}   } }] ).pretty()

 { "_id" : null, "allkeys" : [ "gas", "electric" ] }

mongos> db.test.aggregate([ {"$project":{"akv":{"$objectToArray":"$Cars.gas"}}} ,{$ unwind:"$akv"} ,{ $group:{_id:null , "allkeys":{$addToSet:"$akv.k"} } }]).pretty() { "_id" : null, "allkeys" : [ "USAMade", "OutsideUS" ] }

mongos> db.test.aggregate([   {"$project":{"akv":{"$objectToArray":"$Cars.gas.USAMade"}}} ,{$unwind:"$akv"} ,{ $group:{_id:null , "allkeys":{$addToSet:"$akv.k"}   } }] ).pretty()
{ "_id" : null, "allkeys" : [ "Ford" ] }

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