Implement support for reindex API [DATAES-955]

[spring-projects-issues]

sothawo opened DATAES-955 and commented

IndexOperations should support the reindex API, see linked reference

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Reference URL: https://www.elastic.co/guide/en/elasticsearch/reference/7.9/docs-reindex.html

[spring-projects-issues]

sothawo commented

related SO issue https://stackoverflow.com/questions/64350005/spring-elasticsearch-reindex-method/64365323#64365323

[oni7uka]

I am using reindex api, I can send pull request to implement this enhancement, the implementation is similar to putTemplate, but I have some confusion, reindex and putTemplate are not dependent on a specific index, but the implementation of IndexOperations is RestIndexTemplate which constructor must specify IndexCoordinates or boundClass, It doesn't make sense

[sothawo]

####about putTemplate

Elasticsearch has this under Index APIs that's the reason why it is in the IndexOperations interface. I agree that it makes no sense to have to get an IndexOperations by providing an indexname or class when it is not needed.

We could introduce something like

public class IndexCoordinates {

	public static final IndexCoordinates UNSPECIFIED = IndexCoordinates.of("UNSPECIFIED");
  
	// ...
}

in order to be able to obtain an IndexCoordinates without specifying an index. Using the capitals in the name ensures that this cannot be used in a request that needs an index name.

about reindex

Elasticsearch lists this under Document APIs, so it should go as a method into DocumentOperations and as thus should be implemented in the ElasticsearchTemplate classes. If you want to implement this: we need it in imperative and in reactive code, tests would probably
be integration tests with indexing into one index, then reindex and then read from the second one.

If you wanna do that, give me short notice, I'll mark the issue then as being worked on (although the number of people working on issues is low, almost only me ;-) )

[oni7uka]

Reindex does need to be implemented in DocumentOperations so it seems reasonable. And yes, I will implement this.