LabVIEW
advices for database application
I have been doing something like this for a while. I really do not like php but in all fairness I have not looked at it for several years. What I use is Python on the server through the Django web application framework running on Apache. It is very simple and easy to use.
The LabVIEW code writes data through http POST requests and the server inserts this data into the database. I do not use the Django object relational mapper. Instead I build the SQL inserts manually. I do this mostly because the database already exists and I just find it more natural.
I also do not make use of the Django template engine. The server returns XML to LabVIEW which looks something like this:
<Response>
<Error>
<Cluster>
<Name>error in (no error)</Name>
<NumElts>3</NumElts>
<Boolean>
<Name>status</Name>
<Val>0</Val>
</Boolean>
<I32>
<Name>code</Name>
<Val>0</Val>
</I32>
<String>
<Name>source</Name>
<Val></Val>
</String>
</Cluster>
</Error>
<Data>
<Cluster>
<Name>Hello from server</Name>
<NumElts>3</NumElts>
<String>
<Name>String</Name>
<Val>Hello</Val>
</String>
<Boolean>
<Name>Boolean</Name>
<Val>1</Val>
</Boolean>
<DBL>
<Name>Numeric</Name>
<Val>42.00000000000000</Val>
</DBL>
</Cluster>
</Data>
</Response>
Can you see what I am doing? I am returning an error and a cluster which can be unflattened using Unflatten From XML. I can set LabVIEW errors from Python for things like a request without the required parameters or whatever. I have a Python class that builds the XML Response which contains exactly two children - Error and Data. It has methods including createCluster, addLVObject, createLVArray, insertLVArrayElement, setError, etc. Finally it has a getXMLResponse method which returns the above XML string.
I return that using the Django HTTPResponse object and get at the data in LabVIEW like this
The returned cluster can be as complex as you want such as cluster of cluster of array of cluster. It always returns a cluster so if you want the server to return say an array then you will get a cluster containing an array that you simply unbundle. It supports strings, all the numeric representations, paths, visa resources, boolean and something i am forgetting at the moment.
Also my URL configuration is very simple since I only POST and do not send GET requests. This means I can map the URL directly to the Django view method of the same name. I get the parameters with request.POST.get('Parameter Name')
I know for a fact that you can do all of this with php but I just prefer Python. If none of the above makes sense then come back to it after you read about Django.
Good choice if it was a choice to use PostgreSQL or a stroke of good luck if it was not a choice. This is what I use and it has been rock solid for years. I really want to upgrade because the NOTIFY now supports data payloads. I have had to do some crazy things to get around the fact that the older versions do not support this.
I am thinking seriously about putting together a tutorial on this whole thing.
