Multiple tHashOuts to 1 tHashIn

[mobmsc2]

I have a number of files in 1 folder that have slightly different schemas. I want to standardise the schema before processing all rows as flow. I will need to extend the design to include at least 2 more schema designs not shown here.

I'm having trouble designing the job to unite the flows into 1 while avoiding loops (tUnite doesn't work) so tHash components were suggested but my design as seen below only outputs the rows from 1 of the 4 tHashOut components (whichever is listed as linked in the tHashInput). 

What I've tried

• Adding more tHashInputs and using tUnite to unite the flows but thats creates an error
• Linking multiple tHashInputs to 1 and pairing that tHashInput to the tHashOutput but I get Null pointer exception
• disabling append data but then I get even less rows.

While this reference guide shows 2 HashOuts its not clear to me why the configuration works or how I would extend it to include more tHashOutputs

1. How do I configure multiple tHashOutputs to feed 1 tHashInput?
2. In the tHashOutput component
   1. Does keys management mean the key defined in the schema (and can I have more than 1 key defined in a schema)
   2. What does link to tHashOutput actually mean?
3. In the tHashInput component
   1. Can I link to more than 1 Output as the drop down list only lets me select 1

Anyone able to advise me ?

[Anonymous · Accepted solution]

The way to do this is create a mini subjob at the beginning of your job. In that subjob add a tFixedFlowInput with the schema you require for your files and connect that to a tHashOutput. Set the tFixedFlowInput to produce 0 rows. This will initialise the tHashOutput. 

Now in all of your other tHashOutputs tick the "Link with a tHashOutput" and select the name of the pre-initialised tHashOutput. 

When you want to read from the tHashOutputs connect your tHashInput to the pre-initialised one. 

That is it. 

[mobmsc2]

Thanks thats what I needed, nice trick as well.
Its sometimes not clear "Why" or "How" a setting on a component can be used. As an example The talend help text just confirms "link to a tHashOutput" but does not elaborate as to why you might use or need that