Additional features for searching for value across multiple fields (many-to-one
style)
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Key: LUCENE-1494
URL: https://issues.apache.org/jira/browse/LUCENE-1494
Project: Lucene - Java
Issue Type: New Feature
Components: Search
Affects Versions: 2.4
Reporter: Paul Cowan
Priority: Minor
This issue is to cover the changes required to do a search across multiple
fields with the same name in a fashion similar to a many-to-one database. Below
is my post on java-dev on the topic, which details the changes we need:
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We have an interesting situation where we are effectively indexing two
'entities' in our system, which share a one-to-many relationship (imagine
'User' and 'Delivery Address' for demonstration purposes). At the moment, we
index one Lucene Document per 'many' end, duplicating the 'one' end data, like
so:
userid: 1
userfirstname: fred
addresscountry: au
addressphone: 1234
userid: 1
userfirstname: fred
addresscountry: nz
addressphone: 5678
userid: 2
userfirstname: mary
addresscountry: au
addressphone: 5678
(note: 2 Documents indexed for user 1). This is somewhat annoying for us,
because when we search in Lucene the results we want back (conceptually) are at
the 'user' level, so we have to collapse the results by distinct user id, etc.
etc (let alone that it blows out the size of our index enormously). So why do
we do it? It would make more sense to use multiple fields:
userid: 1
userfirstname: fred
addresscountry: au
addressphone: 1234
addresscountry: nz
addressphone: 5678
userid: 2
userfirstname: mary
addresscountry: au
addressphone: 5678
But imagine the search "+addresscountry:au +addressphone:5678". We'd like this
to match ONLY Mary, but of course it matches Fred also because he matches both
those terms (just for different addresses).
There are two aspects to the approach we've (more or less) got working but I'd
like to run them past the group and see if they're worth trying to get them
into Lucene proper (if so, I'll create a JIRA issue for them)
1) Use a modified SpanNearQuery. If we assume that country + phone will always
be one token, we can rely on the fact that the positions of 'au' and '5678' in
Fred's document will be different.
SpanQuery q1 = new SpanTermQuery(new Term("addresscountry", "au"));
SpanQuery q2 = new SpanTermQuery(new Term("addressphone", "5678"));
SpanQuery snq = new SpanNearQuery(new SpanQuery[]{q1, q2}, 0, false);
the slop of 0 means that we'll only return those where the two terms are in the
same position in their respective fields. This works brilliantly, BUT requires
a change to SpanNearQuery's constructor (which checks that all the clauses are
against the same field). Are people amenable to perhaps adding another
constructor to SNQ which doesn't do the check, or subclassing it to do the same
(give it a protected non-checking constructor for the subclass to call)?
2) It gets slightly more complicated in the case of variable-length terms. For
example, imagine if we had an 'address' field ('123 Smith St') which will
result in (1 to n) tokens; slop 0 in a SpanNearQuery won't work here, of
course. One thing we've toyed with is the idea of using getPositionIncrementGap
-- if we knew that 'address' would be, at most, 20 tokens, we might use a
position increment gap of 100, and make the slop factor 50; this works fine for
the simple case (yay!), but with a great many addresses-per-user starts to get
more complicated, as the gap counts from the last term (so the position
sequence for a single value field might be 0, 100, 200, but for the address
field it might be 0, 1, 2, 3, 103, 104, 105, 106, 206, 207... so it's going to
get out of sync). The simplest option here seems to be changing (or
supplementing)
public int getPositionIncrementGap(String fieldname)
to
public int getPositionIncrementGap(String fieldname, int currentPos)
so that we can override that to round up to the nearest 100 (or whatever) based
on currentPos. The default implementation could just delegate to
getPositionIncrementGap().
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Patches (x2) to follow shortly
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