1. db.cloneCollection()
db.cloneCollection(from, collection, query)
在不同的mongodb實(shí)例間復(fù)制數(shù)據(jù)，db.cloneCollection是cloneCollection數(shù)據(jù)庫命令的一個(gè)外在體現(xiàn)。

function (from, collection, query) {
 assert( isString(from) && from.length );
 assert( isString(collection) && collection.length );
 collection = this._name + "." + collection;
 query = query || {};
 return this._dbCommand( { cloneCollection:collection, from:from, query:query
} );
}