Make ParseContext's IndexQueryParserService accessible

[uschindler]

I have the following problem writing an own query parser from my own package:

My query parser has to internally create another Elasticsaearch query and parse it (which is actually a workaround: I need to create a MoreLikeThis query, but I dont want to replicate all code to generate the native Lucene Query). So I use MoreLikeThisQueryBuilder to create a BytesReference of the newly constructed query, so I can parse it to a Lucene Query.

Of course I cannot do the parseContext.parseInnerQuery, because the newly constructed query is in a separate BytesReference. Instead I do the same trick like WrappedQuery:

    final BytesReference querySource = QueryBuilders.moreLikeThisQuery(FIELDNAME_MLT)
      .ids(Integer.toString(id))
      .include(true)
      .percentTermsToMatch(.5f)
      .minTermFreq(0)
      .minDocFreq(5)
      .maxQueryTerms(25)
      .boostTerms(1.0f)
      .buildAsBytes();
    // hack for parsing this as inner query
    try (XContentParser qSourceParser = XContentFactory.xContent(querySource).createParser(querySource)) {
      final QueryParseContext context = cloneParseContext();
      context.reset(qSourceParser);
      return context.parseInnerQuery();
    } catch (IOException ioe) {
      throw new AssertionError("IOException cannot happen here.", ioe);
    }

The problem is now: I need to clone the QueryParseContext. WrappedQueryParser just creates a new instance, but it needs the index name (easy to get) and IndexQueryParserService. Unfortunately, the latter is package private.

I would be happy if this could be solved. As this above stuff is used quite often, I think the best solution would be to allow to clone ParseContext or add a method to create a new one from an existion one (copy constructor). The other way would be to make the field accessible.

The current workaround is to use reflection to get the field...

[uschindler]

The other "possible" workaround to inject IndexQueryParserService by @Inject into my own query parser does not work (circular dependency).

[kimchy]

why not just expose a getter for indexQueryParser from the parse context? The fact that its package private is not really needed I think.

[uschindler]

@kimchy thats of course the easy thing, as I said :-)

My idea here was to make the common case "parse some other query in context of current ParseContext" easier: The same code is duplicated over and over. Maybe add something like ParseContext#parseQueryInCurrentContext(BytesReference), a setup like parseInnerQuery() - just cloning itsself. By that it could reused in WrapperQueryParser, WrapperFilterParser, and TemplateQueryParser - and for my case.

[kimchy]

The repetition is not terrible if you create a new instance of the QueryParseContext, but we could have a nice helper method, agreed.

Regardless, I don't see a reason why we can't expose the indexQueryParser in the context, which is a very simple change that would help you now (and might get to 1.4), and then look into simplifying the creation of a new instance of QueryParserContext.

[uschindler]

I am fine with exposing that! Add a getter and change the field to private final.

[kimchy]

@uschindler want to send a pull request?

[uschindler]

Can do!