Python: how to find documents with specific fields
I am using python and mongodb. I have a collection containing 40,000 documents. I have a group of coordinates and I need to find which document these coordinates refer to. Now I am doing:
cell_start = citymap.find({"cell_latlng":{"$geoIntersects":{"$geometry":{"type":"Point", "coordinates":orig_coord}}}})
This method is a typical geoJSON method and it works well. Now I know that some docs have a field like this:
{'trips_dest':......}
The value of this field is irrelevant, so I'll just skip that. The point is, instead of searching for documents from all those 40,000 documents, I can simply search for documents from documents with the "trip_dest" field.
Since I know that only about 40% of the documents have a "trip_dest" field, so I think this will improve efficiency. However, I don't know how to change my code to do this. Any idea?
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You need the $ exists query operator. Something like that:
cell_start = citymap.find({"trips_dest": {$exists: true},
"cell_latlng":{"$geoIntersects":{"$geometry":{"type":"Point", "coordinates":orig_coord}}}})
To quote the documentation:
Syntax:
{ field: { $exists: <boolean> } }
When
<boolean>
true,$exists
matches documents containing this field , including documents where the field value is null
If you need to reject null values use:
"trips_dest": {$exists: true, $ne: null}
As a final note, a sparse index may eventually speed up such a query.
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