Return Only Certain Fields From Lucene Search

Question

I'm using Lucene to search an index and it works fine. My only issue is that I only need one particular field of what is being returned. Can you specify to Lucene to only return a certain field in the results and not the entire document?

score 12 · Accepted Answer · edited Oct 11 '22 at 08:24

This is why FieldSelector class exists. You can implement a class like this

class MyFieldSelector : FieldSelector
{
    public FieldSelectorResult Accept(string fieldName)
    {
        if (fieldName == "field1") return FieldSelectorResult.LOAD_AND_BREAK;
        return FieldSelectorResult.NO_LOAD;
    }
}

and use it as indexReader.Document(docid,new MyFieldSelector());

If you are interested in loading a small field, this will prevent to load large fields which, in turn, means a speed-up in loading documents. I think you can find much more detailed info by some googling.

score -2 · Answer 2 · answered Jan 27 '12 at 19:30

-2

What do you mean "return certain fields"? The Document.get() function returns just the field you request.

answered Jan 27 '12 at 19:30

Xodarap

11,581
11
56
94

That's what I'm using now, but I only need one field so I was just wondering if there was a way to only return that field instead of the whole document. – aaron Jan 27 '12 at 19:35
@aaron: I'm still not certain what you mean by "return." The resulting text from `Document.get` is just the text of that one field. If you mean you don't want to store the values of other fields, simply mark them as not stored. – Xodarap Jan 27 '12 at 21:57
-1 but `reader.Document` loads whole document, not just a single field – L.B Jan 28 '12 at 20:06

score -2 · Answer 3 · edited Oct 11 '22 at 08:25

-2

Yes, you can definitely do what you are asking. All you have to do is include the field name (case-sensitive) in the document.get() method.

string fieldNameText = doc.Get("fieldName");

FYI, it's usually a good idea to include some code in your questions. It makes it easier to provide a good answer.

edited Oct 11 '22 at 08:25

Frederik Struck-Schøning

12,981
8
59
68

answered Jan 27 '12 at 21:09

SharpBarb

1,590
3
16
40

I get what you're saying and that's what I'm doing now. I'm trying to limit what fields are included in the doc. – aaron Jan 27 '12 at 21:37
You didnt ask how to limit which fields are included in the doc. You asked how to return a certain field in the results. Im not sure you're aaking the right question. – SharpBarb Jan 27 '12 at 22:25
@SharpBarb, `You asked how to return a certain field in the results. Im not sure you're aaking the right question` Please read the question again after reading my answer. I think I will make sense then – L.B Jan 28 '12 at 22:06

Return Only Certain Fields From Lucene Search

3 Answers3