The prepend() methods insert information before the existing data for a given key. Note that as with the append() method, the information will be inserted before the existing binary data stored in the key, which means that serialization of complex objects may lead to corruption when using prepend().

The prepend() inserts information before the existing data stored in the key/value pair. The prepend() function requires a CAS value. For more information on CAS values, see Section 4.4, “CAS get Methods”.

For example, to prepend a string to an existing key:

CASValue<Object> casv = membase.gets("samplekey");
membase.prepend(casv.getCas(),"samplekey", "prependedstring");

You can check if the append operation succeeded by using the return Future value:

Future<Boolean> success =
    membase.prepend(casv.getCas(),"notsamplekey", "prependedstring");

try {
    if (success.get()) {
        System.out.printf("Prepend succeeded\n");
    }
    else {
        System.out.printf("Prepend failed\n");
    }
}
catch (Exception e) {
...
}

The secondary form of the prepend() method supports the use of a custom transcoder for updating the key/value pair.