myCursor.forEach( function (x) { printjson (x); } ); Previous versions returned a single document with a field results that contained an array of the result set, subject to the BSON Document size limit. Accessing the result set in the previous versions of MongoDB required accessing the results field and iterating the array. For example: MongoDB Documentation, Release 3.0.4 var returnedDoc = db.orders.aggregate( [ { $group: { _id: "$cust_id", total: { $sum: "$price" } } } ] ); var myArray = returnedDoc.result; // access the result field myArray.forEach( function (x) { printjson (x); } ); Solution Update scripts that currently expect db.collection.aggregate() to return a document with a results array to handle cursors instead. Description Specifying a write concern that includes j: true to a mongod or mongos instance running with --nojournal option now errors. Previous versions would ignore the j: true . Solution Either remove the j: true specification from the write concern when issued against a mongod or mongos instance with --nojournal or run mongod or mongos with journaling. Write Concern Validation See also: Aggregation Enhancements (page 851), db.collection.aggregate() , Security Changes New Authorization Model Description MongoDB 2.6 authorization model (page 324) changes how MongoDB stores and manages user privi- lege information: Solution Ensure that at least one user exists in the admin database. If no user exists in the admin database, add a user. Then upgrade to MongoDB 2.6. Finally, upgrade the user privilege model. See Upgrade MongoDB to 2.6 (page 866). • Before the upgrade, MongoDB 2.6 requires at least one user in the admin database. • MongoDB versions using older models cannot create/modify users or create user-defined roles. Important: Before upgrading the authorization model, you should first upgrade MongoDB binaries to 2.6. For sharded clusters, ensure that all cluster components are 2.6. If there are users in any database, be sure you have at least one user in the admin database before upgrading the MongoDB binaries. Security Improvements (page 852) See also: 859 12.2. Previous Stable Releases