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MarkLogic node.js - conditional updates using fields other than versionId

I'm using ML8 and Node.js. The documentation here: http://docs.marklogic.com/guide/node-dev/documents#id_68765 describes how to do conditional updates in ML using the versionId field.

But for example if I want to do a conditional update on a different field, is it possible?

My scenario is: I have JSON documents with elements assignedTo and assignDate (where assignDate is set to current date every time a new value is set to assignedTo)

Now, for my "Assign" operation, I would like to make sure that no one else has changed the assignedTo/assignDate fields between the time I read the document and when I perform the update. I don't care if other fields in the same document have been updated or not - if other fields have been updated, I can still proceed with the Assign operation (hence I cannot use the versionId approach, since that covers the whole document)

How can this be done?

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Last modified at: Jan. 17, 2021, 5:10 a.m. Source file

Comments

ehennum
ehennum said...

Optimistic locking doesn't look at the content of the document. Instead, the version id is a system value reflecting the timestamp on the document. Checking the timestamp is more efficient than reading the document content.

You could write a POST resource service extension that

  • receives the update content
  • reads the document and checks that assignTo/ assignDate haven't changed
  • does an xdmp:node-replace() on the root of the document with the update content

Hoping that helps,