mongo console: how to print an element's internal type
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20-12-2019 - |
Frage
With $type and $match, I can find iteratively discover what types Mongo thinks my data has. With $not, I can get the results even faster sometimes.
Is there a way to project the type of an element in a document directly? (I presume I could get it with pymongo, but I haven't looked there yet.) thank you!
Lösung
Well you could sort of do this with mapReduce. I can demonstrate for simplicity but complex structures would take more implementation to actually work through recursively.
So given a document.
db.team.find()
{
"_id" : 50,
"team_name" : "bulls",
"players" : [
{
"_id" : 100,
"player_name" : "Jokim"
}
],
"sub" : {
"opt" : 1
},
"long" : NumberLong(123),
"int" : 1,
"bool" : false,
"date" : ISODate("2014-06-03T01:42:01.016Z"),
"unset" : null,
"id" : ObjectId("538d36ccb88d0a9b6195ca66")
}
You could run this "basic" mapper:
db.team.mapReduce(
function () {
var obj = {};
for ( var k in this ) {
var type = ( this[k] != null )
? this[k].constructor.toString() : null;
var match = null;
if (type != null)
match = type.match(/^function\s(\w+)/);
obj[k] = ( match != null ) ? match[1]
: ( type != null ) ? 'Object' : null;
}
emit( this._id, obj );
},
function(){},
{ "out": { "inline": 1 } }
)
Which gives you output like this:
"results" : [
{
"_id" : 50,
"value" : {
"_id" : "Number",
"team_name" : "String",
"players" : "Array",
"sub" : "Object",
"long" : "NumberLong",
"int" : "Number",
"bool" : "Boolean",
"date" : "Date",
"unset" : null,
"id" : "ObjectId"
}
}
],
You can take that as far as you need, going recursively into "Array" or "Object" ( sub-document ) types. But that is one way to output a "type" for the given field/property.