Modifying vs. replacing documents

Updates

Updates can be one of the most complicated operation available with MongoDB. They combine a query with an action, modifying documents that match the criteria. They are also extremely powerful, allowing you to change documents quickly and replace them altogether. They are done in-place (when possible) with little overhead.

Modifying vs. replacing documents

There are two types of updates you can use: modifying updates and replacing updates. Modifying updates contain $-operators and change fields in a document: they might increment counters, push new elements onto an array, or change the type of a field.

For example, a modifying update could add a new field to a document.

/** suppose documents look like:
 * {"username" : "...", "password" : "...", "email" : "..."}
 */$coll->update(array("username" => "joe"), array('$set' => array("twitter" => "@joe4153")));/** now the document will look like:
 * {"username" : "joe", "password" : "...", "email" : "...", "twitter" : "@joe4153"}
 */?>

Replacing updates replace the entire matching document with a new document. They are generally not as efficient as using $-modifiers, but can be very usefully for complex operations or updates that can't be expressed in terms of $-operators.

For example, a replacing update can completely change the structure of a document.

/** suppose documents look like:
 * {"username" : "...", "password" : "...", "email" : "..."}
 */$coll->update(array("username" => "joe"), array("userId" => 12345, "info" => array(
    "name" => "joe", "twitter" => "@joe4153", "email" => "..."), "likes" => array()));/** now the document will look like:
 * {
 *     "userId" : 12345,
 *     "info" : {
 *         "name" : "joe",
 *         "twitter" : "@joe4153",
 *         "email" : "..."
 *     },
 *     "likes" : []
 * }
 */?>