MongoDB Python – How to Get Minimum Value in pyMongo

mongodbpython

I have a collection with several fields, and I'd like to get the minimum value from one. I know a command for getting the max value:

collection.find_one(sort=[("myfield", -1)])["myfield"]

but not one for getting the min. Is there a way to do this?

Best Answer

You can reverse the sort direction to get the minimum instead of the maximum value:

 # Sort by myfield (ascending value) and return first document
 collection.find_one(sort=[("myfield", 1)])["myfield"]

This example assumes that:

myfield is a numeric value (so the sort order makes sense to determine a minimum or maximum)
myfield exists in the matching document returned (otherwise Python will report a KeyError when trying to reference a non-existent field).
all documents in the collection have a myfield value (documents that have do not have a myfield value will sorted before the minimum numeric values)

To ensure your sort is based on documents that actually have a myfield value you can add $exists to the query criteria:

 collection.find_one({"myfield": {"$exists": True}}, sort=[("myfield", 1)])["myfield"]

For more information on sorting see:

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I ended up using this command:

mongo --quiet --eval "var c=new Mongo();var o=[];db.adminCommand('listDatabases').databases.forEach(function(d){o=o.concat(c.getDB(d.name).currentOp(true).inprog.filter(function(d){return d.op=='query';}).map(function(d){return d.query;}));});o" > cursor.json

The expanded form of the actual js in there is

var conn = new Mongo();
var cursorInfo = [];
db.adminCommand('listDatabases').databases.forEach(function(d) {
    var database = conn.getDB(d.name)
    cursorInfo = cursorInfo.concat(database.currentOp(true).inprog.filter(function(d) {
                return d.op == 'query';
            }).map(function(d) {
                return d.query;
            }));
});
cursorInfo

The command will get the information from db.currentOp(true).inprog about current querying cursors for every db and save it into the file cursor.json.

Best Answer

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