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Using Conditional Updates

Sometimes several clients can request updates to the same infoton at the same time. This can result in one client's updates overwriting another client's updates.

If you want to make sure that an infoton has not changed between the time that you retrieved its UUID and data and the time that your updates are made, you can use the conditional update feature. To use this feature, when requesting an update, you provide the infoton's UUID within the request. CM-Well only performs the update if the infoton's UUID is the same as the one you provided. If it's different, this indicates that another client has updated the infoton since the last time you read it.

To provide the infoton's UUID, you add a triple with the following format to your update request:

<Infoton URI> <cmwell://meta/sys#prevUUID> <Infoton UUID>

For example:

Request:

<cm-well-host>/_in?format=ntriples

Input triples:

<http://infoton.int.com/example/1> <cmwell://meta/sys#prevUUId> "afb215df2b6356d8801aq10a6c764d3a" .
    <http://infoton.int.com/example/1> <http://infoton.int.com/object/name> "My New Name" .

Note

An update request using the conditional feature receives a "success" response as long as the request is valid. To find out whether the update succeeded, you'll have to use the blocking flag or the tracking API. If the update failed because of a parallel update, a blocking update request or tracking request will produce an Evicted Version status.