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  1. Lucene - Core
  2. LUCENE-6005

Explore alternative to Document/Field/FieldType API


    • Bug
    • Status: Open
    • Major
    • Resolution: Unresolved
    • None
    • 6.0
    • None
    • None
    • New


      Auto-prefix terms (LUCENE-5879) is blocked because it's impossible in
      Lucene today to add a simple API to use it, and I don't think we
      should commit features that only super-experts can figure out how to
      use: that's evil.

      The only realistic "workaround" for such new features is to instead
      add them directly to the various servers on top of Lucene, since they
      all already have nice schema APIs.

      I opened LUCENE-5989 to try do at least a baby step towards making it
      easier to use auto-prefix terms, so you can easily add singleton
      binary tokens, but even that has proven controversial.

      Net/net I think we have to solve the root cause of this by fixing the
      Document/Field/FieldType API so that new index-level features can have
      a usable API, properly defaulted for the right types of fields.

      Towards that, I'm exploring a replacement for
      Document/Field/FieldType. The idea is to expose simple methods on the
      document class (no more separate Field and FieldType classes):

          doc.addLargeText("body", "some text");
          doc.addShortText("title", "a title");
          doc.addAtom("id", "29jafnn");
          doc.addBinary("bytes", new byte[7]);
          doc.addNumber("number", 17);

      And then expose a separate FieldTypes class, that you pass to ctor of
      the new document class, which lets you set all the various per-field
      settings (stored, doc values, etc.). E.g.:


      FieldTypes is a write-once schema, and it throws exceptions if you try
      to make invalid changes once a given setting is already written
      (e.g. enabling norms after having disabled them). It will (I haven't
      implemented this yet) save its state into IndexWriter's commitData, so
      it's available when you open a new IndexWriter for append and when you
      open a reader.

      It has methods to set all the per-field settings (analyzer, stored,
      term vectors, norms, index options, doc values type), and chooses
      "reasonable" defaults based on the value's type when it suddenly sees
      a new field. For example, when you add a number, it's indexed for
      range querying and sorting (numeric doc values) by default.

      FieldTypes provides the analyzer and codec (a little messy) that you
      pass to IndexWriterConfig. Since it's effectively a persistent
      schema, it knows all about the available fields at search time, so we
      could use it to create queries (checking if they are valid given that
      field's type). Query parsers and highlighters could consult it.
      Default UIs (above Lucene) could use it, etc. This is all future .. I
      think for this issue the goal should be to "just" provide a "better"
      index-time API but not yet make use of it at search time.

      So with this change, for auto-prefix terms, we could add an "enable
      range queries/filters" option, but then validate that the selected
      postings format supports such an option.

      I know this exploration will be horribly controversial, but
      realistically I don't think Lucene can move on much further if we
      can't finally address this schema problem head on.

      This is long overdue.




            mikemccand Michael McCandless
            mikemccand Michael McCandless
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