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From Fabian Hueske <fhue...@gmail.com>
Subject Re: Using a POJO class wrapping an ArrayList
Date Wed, 16 Mar 2016 09:03:52 GMT
Hi Mengqi,

I did not completely understand your use case.

If you would like to use a composite key (a key with multiple fields) there
are two alternatives:
- use a tuple as key type. This only works if all records have the same
number of key fields. Tuple serialization and comparisons are very
efficient.
- implement your own type (like you did) but override the compare() method.
Here you can also deal with different number of key fields. A custom type
will be serialized with Kryo. You can make it more efficient if you
register the type in the ExecutionConfig.

If you want to use multiple keys for a record, you need to emit the record
multiple times in a FlatMapFunction and assign each time a different key.

Hope this helps,
Fabian


2016-03-14 10:43 GMT+01:00 Mengqi Yang <melody2014ymq@gmail.com>:

> Hi all,
>
> Now I am building a POJO class for key selectors. Here is the class:
>
> public class Ids<K> implements Comparable, Serializable{
>
>         private static final long serialVersionUID = 1L;
>
>         private ArrayList<K> ids = new ArrayList<K>();
>
>         Ids() {}
>
>         Ids(ArrayList<K> inputIds) {
>                 this.ids = inputIds;
>         }
>
> }
>
> And the question is, how could I use each element in the array list as a
> field for further key selection? I saw the typeinfo of Flink takes the
> field
> of arraylist as 1. Or maybe I didn't understand it correctly.
>
> Thanks,
> Mengqi
>
>
>
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