Using a POJO class wrapping an ArrayList

[Mengqi Yang]

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

[Fabian Hueske-2]

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 <[hidden email]>:

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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