Syntax
Examples
Input
Pipeline
db.coll.aggregate([{
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$project: {
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_id: {$type: "$_id"}
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}
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}])
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Output
Additional Notes
- Type names will match the query $type operator.
- Note in a query, the $type will try to match elements inside of an array, so a {$type: 'array'} will only match nested arrays. This will not be the case in aggregation. The type of an array will be 'array'.
- Adding a $in expression (
SERVER-6146) and a $switch expression (SERVER-10689) should make it easier to tell if something is numeric.
Original Description
If there was an equivalent of $type field (it can return bson type number or something else) it would be highly useful to do appropriate processing only if a field is a particular type.
For example, without knowing if a field is always an array, it's possible to get an error trying to $unwind or to get $size - if you could
{$project: {typeOfFoo:{$type:"$foo"}}}
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you could now do different processing/operations depending on whether type is an array or not, or if it's a string vs number vs date, etc.