Please find attached a small test case to demonstrate what I mean. There
is just some nonsense Business Object class and a simple test case in
this fileout.
Am 04.01.21 um 14:36 schrieb jtuc...@objektfabrik.de:
Happy new year to all of you! May 2021 be an increasingly less crazy
year than 2020...
I have a question that sounds a bit strange, but we have two effects
with NeoCSVReader related to wrong definitions of the reader.
One effect is that reading a Stream #upToEnd leads to an endless loop,
the other is that the Reader produces twice as many objects as there
are lines in the file that is being read.
In both scenarios, the reason is that the CSV Reader has a wrong
number of column definitions.
Of course that is my fault: why do I feed a "malformed" CSV file to
poor NeoCSVReader?
Let me explain: we have a few import interfaces which end users can
define using a more or less nice assistant in our Application. The CSV
files they upload to our App come from third parties like payment
providers, banks and other sources. These change their file structures
whenever they feel like it and never tell anybody. So a CSV import
that may have been working for years may one day tear a whole web
server image down because of a wrong number of fieldAccessors. This is
bad on many levels.
You can easily try the doubling effect at home: define a working CSV
Reader and comment out one of the addField: commands before you use
the NeoCSVReader to parse a CSV file. Say your CSV file has 3 lines
with 4 columns each. If you remove one of the fieldAccessors, an
#upToEnd will yoield an Array of 6 objects rather than 3.
I haven't found the reason for the cases where this leads to an
endless loop, but at least this one is clear...
I *guess* this is due to the way #readEndOfLine is implemented. It
seems to not peek forward to the end of the line. I have the gut
feeling #peekChar should peek instead of reading the #next character
form the input Stream, but #peekChar has too many senders to just go
ahead and mess with it ;-)
So I wonder if there are any tried approaches to this problem.
One thing I might do is not use #upToEnd, but read each line using
PositionableStream>>#nextLine and first check each line if the number
of separators matches the number of fieldAccessors minus 1 (and go
through the hoops of handling separators in quoted fields and
such...). Only if that test succeeds, I would then hand a Stream with
the whole line to the reader and do a #next.
This will, however, mean a lot of extra cycles for large files. Of
course I could do this only for some lines, maybe just the first one.
Whatever.
But somehow I have the feeling I should get an exception telling me
the line is not compatible to the Reader's definition or such. Or
#readAtEndOrEndOfLine should just walk the line to the end and ignore
the rest of the line, returnong an incomplete object....
Maybe I am just missing the right setting or switch? What best
practices did you guys come up with for such problems?
Thanks in advance,
Joachim
--
-----------------------------------------------------------------------
Objektfabrik Joachim Tuchel mailto:jtuc...@objektfabrik.de
Fliederweg 1 http://www.objektfabrik.de
D-71640 Ludwigsburg http://joachimtuchel.wordpress.com
Telefon: +49 7141 56 10 86 0 Fax: +49 7141 56 10 86 1
Object subclass: #AwesomeBusinessObject
instanceVariableNames: 'shortText value count longText'
classVariableNames: ''
package: 'NeoCSVEndlessLoopTest'!
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:04'!
longText: anObject
longText := anObject! !
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:04'!
shortText
^ shortText! !
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:04'!
shortText: anObject
shortText := anObject! !
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:04'!
value: anObject
value := anObject! !
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:04'!
count: anObject
count := anObject! !
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:05'!
value
^ value! !
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:04'!
longText
^ longText! !
!AwesomeBusinessObject methodsFor: 'accessing' stamp: 'JoachimTuchel 1/4/2021
14:04'!
count
^ count! !
TestCase subclass: #NeoCSVEndlessLoopTestCase
instanceVariableNames: 'reader'
classVariableNames: ''
package: 'NeoCSVEndlessLoopTest'!
!NeoCSVEndlessLoopTestCase methodsFor: 'running' stamp: 'JoachimTuchel 1/4/2021
14:42'!
setUp
super setUp.
reader := NeoCSVReader new.
reader separator: $;.
reader recordClass: AwesomeBusinessObject .
reader addField: #shortText:.
" reader addField: #value: converter: [:inp| ScaledDecimal fromString:
inp].
" reader addField: #count:.
reader addField: #longText:.
reader on: (ReadStream on: self input).! !
!NeoCSVEndlessLoopTestCase methodsFor: 'running' stamp: 'JoachimTuchel 1/4/2021
14:08'!
input
^'"Line1";"15.0s2";3000;"Smalltalk is cool"
"Line2";"25.3s3";1000;"JavaScript is said to be cool"
"Line 3";"1.0s2";8000;"Python seems to wipe the all from the table"'! !
!NeoCSVEndlessLoopTestCase methodsFor: 'running' stamp: 'JoachimTuchel 1/4/2021
14:07'!
testWrongNumberOfObjects
| objects |
objects := reader upToEnd.
self assert: (objects size = 3).
self assert: (objects allSatisfy: [:ea | ea longText isEmptyOrNil
not])! !
