In MongoDB, using $type
, it is possible to filter a search based on if the field matches a BSON data type (see DOCS ).
For eg.
db.posts.find({date2: {$type: 9}}, {date2: 1})
which returns:
{
"_id" : ObjectId("4c0ec11e8fd2e65c0b010000"),
"date2" : "Fri Jul 09 2010 08:25:26 GMT"
}
I need a query that will tell me what the actual type of the field is, for every field in a collection. Is this possible with MongoDB?
Starting from MongoDB 3.4, you can use the $type
aggregation operator to return a field's type.
db.posts.aggregate(
[
{ "$project": { "fieldType": { "$type": "$date2" } } }
]
)
which yields:
{
"_id" : ObjectId("4c0ec11e8fd2e65c0b010000"),
"fieldType" : "string"
}
type the below query in mongo shell
typeof db.employee.findOne().first_name
Syntax
typeof db.collection_name.findOne().field_name
OK, here are some related questions that may help:
Get all field names in a collection using map-reduce.
Here's a recursive version that lists all possible fields.
Hopefully that can get you started. However, I suspect that you're going to run into some issues with this request. There are two problems here:
$type
, but it doesn't look like you can actually run a gettype
function on a field and have that maps back to the BSON type.So if you assume that you can solve problem #1, then you should be able to solve problem #2 using a slight variation on "Get all field Names" .
It would probably look something like this:
"map" : function() { for (var key in this) { emit(key, [ typeof value[key] ]); } }
"reduce" : function(key, stuff) { return (key, add_to_set(stuff) ); }
So basically you would emit the key
and the type of key value
(as an array) in the map function. Then from the reduce function you would add unique entries for each type.
At the end of the run you would have data like this
{"_id":[255], "name" : [1,5,8], ... }
Of course, this is all a lot of work, depending on your actual problem, you may just want to ensure (from your code) that you're always putting in the right type of data. Finding the type of data after the data is in the DB is definitely a pain.
Noting that a=5;a.constructor.toString()
prints function Number() { [native code] }
, one can do something similar to:
db.collection.mapReduce(
function() {
emit(this._id.constructor.toString()
.replace(/^function (\S+).+$/, "$1"), 1);
},
function(k, v) {
return Array.sum(v);
},
{
out: { inline: 1 }
});
Taking advantage of the styvane query, I added a $group listing to make it easier to read when we have different data types.
db.posts.aggregate(
[
{ "$project": { _id:0, "fieldType": { "$type": "$date2" } } },
{"$group": { _id: {"fieldType": "$fieldType"},count: {$sum: 1}}}
])
And have this result:
{ "_id" : { "fieldType" : "missing" }, "count" : 50 }
{ "_id" : { "fieldType" : "date" }, "count" : 70 }
{ "_id" : { "fieldType" : "string" }, "count" : 10 }
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.