Github user mattyb149 commented on a diff in the pull request:
https://github.com/apache/nifi/pull/2003#discussion_r127120413
--- Diff:
nifi-nar-bundles/nifi-standard-services/nifi-record-serialization-services-bundle/nifi-record-serialization-services/src/main/java/org/apache/nifi/csv/CSVRecordSetWriter.java
---
@@ -48,6 +54,7 @@
@Override
protected List<PropertyDescriptor> getSupportedPropertyDescriptors() {
final List<PropertyDescriptor> properties = new
ArrayList<>(super.getSupportedPropertyDescriptors());
+ properties.add(CSVUtils.EXPLICIT_COLUMNS);
--- End diff --
Sorry this is the wrong spot to leave the comment but since
@CapabilityDescription (line 40/46) wasn't part of the diff, I couldn't leave
the comment there. Setting Explicit Columns can affect the first line written,
so the CapabilityDescription text should be updated to include that.
In addition, explicitly setting the output columns is subject to the same
rules as if you had an output Avro schema; namely, the output field/column
names have to match the input names or else there will be empty columns/fields
in the output. In the general case this is covered by processor or
reader/writer doc, but since this is CSV-specific I think we should make this
clear. On one hand, there is the interesting feature that columns can be
re-arranged by specifying the input fields in a different order in the explicit
output columns; but on the other hand, if the user expects to use the writer to
rename the fields (because the names are positional), that won't work.
In general, I'd like this extra flexibility/power to not be too confusing
for the user, or its usefulness will be overshadowed by its complexity. For
example, you can use the Explicit Columns in the CSVReader to rename the
columns, and in the CSVRecordSetWriter to reorder the columns, but the inverse
is not true. These could remain undocumented/unsupported features, and/or we'd
need very clear documentation explaining their use.
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