问题

I wonder know how to return the specified embedded keys ?

by the similar query

db.collection.find({"table_name": "change_in_real_gdp", {"data.*.actual":1, "data.*. upper_end_of_range"}})

Original document

{
  "_id": "2012-06-20_change_in_real_gdp",
  "table_name": "change_in_real_gdp",
  "data": {
    "2007": {
      "actual": "4.8",
      "upper_end_of_range": "-",
      "upper_end_of_central_tendency": "-",
      "lower_end_of_central_tendency": "-",
      "lower_end_of_range": "-"
    },
    "2008": {
      "actual": "6.9",
      "upper_end_of_range": "-",
      "upper_end_of_central_tendency": "-",
      "lower_end_of_central_tendency": "-",
      "lower_end_of_range": "-"
    }
    }
}

Expected result

{
  "_id": "2012-06-20_change_in_real_gdp",
  "table_name": "change_in_real_gdp",
  "data": {
    "2007": {
      "actual": "4.8",
      "upper_end_of_range": "-",
    },
    "2008": {
      "actual": "6.9",
      "upper_end_of_range": "-",
    }
    }
}

回答1:

You cannot use regex in projection. You need to explicitly specify the projection argument to the .find() method

db.collection.find({}, 
    { 
        "data.2007.actual": 1, 
        "data.2007.upper_end_of_range": 1, 
        "data.2008.actual": 1, 
        "data.2008.upper_end_of_range": 1, 
        "table_name": 1 
    }
)

回答2:

it can be achieve using query manipulation

so i have attached some code to achieve this

var projection = '{';
var start_year = 2007;
var end_year = 2008;

for(var counter=start_year;counter<=end_year;counter++) {
    var attr1 = "\"data."+counter+".actual\"";
    var attr2 = "\"data."+counter+".upper_end_of_range\"";
    projection += attr1+':1,'+attr2+':1';
    if(counter !== end_year)
    projection += ',';
    else 
    projection += '}';    
}
var obj = JSON.parse(projection);
db.people.find({"table_name": "change_in_real_gdp"},obj);

Thanks

来源：https://stackoverflow.com/questions/29250081/how-to-projection-filter-embedded-keys-with-applying-regex-on-key

标签

mongodb