[
https://issues.apache.org/jira/browse/FLINK-5299?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15735864#comment-15735864
]
Chesnay Schepler commented on FLINK-5299:
-----------------------------------------
That's a good question. I've looked into it a bit more and think now that my
original idea was kinda bad actually :/ (since i pretty much only accounted for
the case of a single key which is some array)
What we could maybe do is the following (note that this is completely theory, i
haven't tried out anything):
Add a new method to the TypeComparator that extracts a hash-stable Key:
{code}
public int extractHashStableKeys(Object record, Object[] target, int index) {
return extractKeys(record, target, index); // to not break existing
implementations
}
{code}
The TupleComparator implementation would look like this: (it is identical to
extractKeys, except that it calls extractHashStableKeys)
{code}
@Override
public int extractHashStableKeys(Object record, Object[] target, int index) {
int localIndex = index;
for(int i = 0; i < comparators.length; i++) {
localIndex += comparators[i].extractHashStableKeys(((Tuple)
record).getField(keyPositions[i]), target, localIndex);
}
return localIndex - index;
}
{code}
Finally, we add the following method to the primitive array comparator:
{code}
@Override
public int extractHashStableKeys(Object record, Object[] target, int index) {
target[index] = Arrays.hashCode(record);
return 1;
}
{code}
There you go.
> DataStream support for arrays as keys
> -------------------------------------
>
> Key: FLINK-5299
> URL: https://issues.apache.org/jira/browse/FLINK-5299
> Project: Flink
> Issue Type: Improvement
> Components: DataStream API
> Affects Versions: 1.2.0
> Reporter: Chesnay Schepler
> Labels: star
>
> It is currently not possible to use an array as a key in the DataStream api,
> as it relies on hashcodes which aren't stable for arrays.
> One way to implement this would be to check for the key type and inject a
> KeySelector that calls "Arrays.hashcode(values)".
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
