Class DataFunction

source code

                   object --+                    
                            |                    
 base.structure.StructureBase --+                
                                |                
                   object --+   |                
                            |   |                
           base.common.Parser --+                
                                |                
base.structure.ParseableStructure --+            
                                    |            
             base.structure.Structure --+        
                                        |        
                           object --+   |        
                                    |   |        
      base.structure.RestrictionMixin --+        
                                        |        
                   rscdef.procdef.ProcDef --+    
                                            |    
                       rscdef.procdef.ProcApp --+
                                                |
                                               DataFunction

A procedure application that generates or modifies data in a processed data service.

All these operate on the data attribute of the product descriptor. The first data function plays a special role: It *must* set the data attribute (or raise some appropriate exception), or a server error will be returned to the client.

What is returned depends on the service, but typcially it's going to be a table or products.*Product instance.

Data functions can shortcut if it's evident that further data functions can only mess up (i.e., if the do something bad with the data attribute); you should not shortcut if you just *think* it makes no sense to further process your output.

To shortcut, raise either of FormatNow (falls though to the formatter, which is usually less useful) or DeliverNow (directly returns the data attribute; this can be used to return arbitrary chunks of data).

The following names are available to the code:

• descriptor -- whatever the DescriptorGenerator returned
• args -- all the arguments that came in from the web.

In addition to the usual names available to ProcApps, data functions have:

• FormatNow -- exception to raise to go directly to the formatter
• DeliverNow -- exception to raise to skip all further formatting and just deliver what's currently in descriptor.data
• File(path, type) -- if you just want to return a file on disk, pass its path and media type to File and assign the result to descriptor.data.
• TemporaryFile(path,type) -- as File, but the disk file is unlinked after use
• makeData -- the rsc.makeData function
• soda -- the protocols.soda module