Flatten nested documents as part of re-index process (using painless)

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Hi... we have a nested mapping, which we'd like to reindex into a non-nested structure -
i.e. each nested object + the 'parent' document becomes a new document.

Is this possible by reindexing this structure using painless?

I tried to follow the guidelines from the URL below, but the problem is that by iterating the nested inner documents array within the parent, and assigning "ctx_source" fields the relevant values from the inner object, each document overrides the previous, so that at the end of the update, we only get a single document with the values from the last nested document it holds.

here is an example of a painless code as we tried to use it -

if (ctx._source.nestedObject instanceof List)  {
	for (int i = 0; i < ctx._source.nestedObject.size(); i++) {
            ctx._source.text=ctx._source.nestedObject[i].text;
            ctx._source.lineNumber=ctx._source.nestedObjectinstanceof [i].lineNumber;
            ctx._source.someProperty=ctx._source.nestedObject [i].someProperty;
        }

Is there a way to flatten the nested documents as we want? so that if for example, we have a 1 outer document with 10 nested documents inside, at the end of the reindex process, we will have 10 flatten documents?

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