UDFs are not serialized from the frontend to the backend, so simply
saving the schema into a variable will not work.
What version of Pig are you using? In 0.6 and later the UDFContext
class exists to allow UDFs to carry information like this from the
frontend to the backend.
Alan.
On May 22, 2010, at 9:10 AM, Alexander Schätzle wrote:
Hi all,
in the exec(Tuple input) method of an EvalFunc I get the tuple to be
processed by the Eval Function.
Is there any secure possibility to get the Aliases of the fields in
the input Tuple?
My Eval Function needs to know the names of the Field-Aliases in
order to know how to evaluate the tuple.
My current solution is to save the Schema which I get in the
outputSchema(Schema input) method in a static instance variable of
the Eval Function Class so that I can access the Schema-Information
in the exec-method:
private static Schema inputSchema;
public Schema outputSchema(Schema input) {
inputSchema = input;
return input;
}
public Tuple exec(Tuple input) throws IOException {
Set<String> aliases = inputSchema.getAliases();
...
return input;
}
Local tests worked but I'm not sure if it is guaranteed to work?
Example:
Describe A;
A: {varName1: chararray, varName2: chararray}
B = Foreach A Generate MyUDF(*);
In MyUDF I have to know the name of the first and second field
(varName1 and varName2) because the processing is dependant on the
varNames.
Any suggestions?
Thx in advance,
Alex
