_mongodb_scripts

# a set of useful scripts for mongodb

- batch deleting collections
- extract subset using fast aggregation method
- export query to csv (quick and dirty)

mongodb_batch_delete_collection

var collectionNames = db.getCollectionNames();

for(var i = 0, len = collectionNames.length; i < len ; i++){
  var collectionName = collectionNames[i];
  if(collectionName.indexOf('NAMESTARTS_') == 0){
    db[collectionName].drop()
  }
}

mongodb_dump_collection

mongodump --db database_name --collection collection_name --out - | gzip > dump_file_name.gz

mongodb_export_to_csv

mongoexport -d DB -c COLL --type=csv --out file_name.csv --fields f1,f2,f3

mongodb_extract_subset

db.getCollection('FULL_SET').aggregate([{ $match:{ FIELD:"VALUE"} }, { $out: "SUB_SET" }]);

mongodb_get_last_record

db.collection.find().limit(1).sort({$natural:-1})

mongodb_mapreduce_histogram

db.COLLECTION_NAME.mapReduce(
    function(){
        var lat = Math.floor(this["loc"]["lat"]);
        var lon = Math.floor(this["loc"]["lng"]);
        var key = lat + "_" + lon;
        emit(key, {count: 1})
    }, 
    function(state, values){
        var result = {count: 0};
        values.forEach(function(value) {
            result.count += value.count;
        });
        return result;
    }, 
    {out: "histogram"}
);

mongodb_move_collection

use admin

db.runCommand({renameCollection:"sourcedb.mycol",to:"targetdb.mycol"})

mongodb_query_to_csv

 mongoexport -d DBNAME -c COLLNAME --query "{'FIELD':'VLAUE'}" --type=csv --fields F1,F2,F3 --out out.csv