Invalid property? A Trick With vSphere PropertyCollector
As I discussed extensively in my book, the PropertyCollector is very powerful yet not easy to use. There was a question posted at vSphere Java API forum related to the property collector which I think worths sharing here. Although it’s found using vSphere Java API, but it really goes beyond the API to the vSphere API itself.
The problem was not able to retrieve the info.vmfs property of a Datastore managed object using vSphere Java API, but OK with others like info.freeSpace, info.maxFileSize, info.name, etc. If MOB is used, the info.vmfs can be retrieved without any problem.
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vSphere Java API wraps up the PropertyCollector using getter methods for all the direct properties in very managed object. Mostly you don’t need to touch the PropertyCollector at all.
In some cases, you do want to get hold of the sub properties directly to save CPU cycle and bandwidth. That is why I decided to open up the getPropertyByPath() method with which you can provide the property path and get the value in one call.
Now, what is the cause of the problem?
It’s related the typing of the property. The info property is typed as DatastoreInfo. It does NOT have a sub property called vmfs. But DatastoreInfo is an abstract type which is extended to VmfsDatastoreInfo which does have vmfs sub property. There are other possibilities, for example, DatastoreInfo to NasDatastoreInfo which does NOT have vmfs sub property at all. So before being certain about the real type, we cannot request for info.vmfs.
How to solve this issue?
It’s pretty easy. You want to get the info with getInfo() method, and check the instance type before casting it to VmfsDatastoreInfo. Once it’s casted, you can use the vmfs as easy as one getVmfs() call.