Filter on empty string using ElasticSearch/Nest

Question

This may be a silly question, but how do I filter on an empty string in ElasticSearch using Nest. Specifically, how do I recreate the following result:

curl http://localhost:9200/test/event/_search
{
    "filter" : { "term" : { "target" : "" }}
}

I've tried:

(f => f
    .Term("target", "")
);

which according to ElasticSearch and Nest filtering does not work is treated like a conditionless query and returns everything, while adding a .Strict() throws a DslException:

(f => f
    .Strict().Term("target", "")
);

I've also tried .Missing() and .Exists() to no avail.

The relevant section of my _mapping for reference:

{
    "event": {
        "dynamic": "false",
        "properties": {
            target": {
                "type": "string",
                "index": "not_analyzed",
                "store": true,
                "omit_norms": true,
                "index_options": "docs"
            }
        }
    }
}

Any pointers would be greatly appreciated.

Dont know why the src always throw DslException if Strict = true, but you can send the request "filter" : { "term" : { "target" : "" }} directly using QueryRaw/FilterRaw — Duc.Duong
– Duc.Duong, Commented Dec 4, 2013 at 4:08
Thanks, I'm trying to avoid that since it would take a sizeable refactor on my end. I was hoping there was some magic I was missing. — user1664295
– user1664295, Commented Dec 5, 2013 at 3:16
I think you can post a bug to NEST to get helped. Maybe the author can suggest some better alternatives. — Duc.Duong
– Duc.Duong, Commented Dec 6, 2013 at 8:41
This is not a use case I envisioned but it's a really valid one. I'm working on adding .Verbatim() as a counter part to .Strict() which will not throw or remove the query if its conditionless but leave it as as defined. I will post an answer when its up on github. — Martijn Laarman
– Martijn Laarman, Commented Dec 6, 2013 at 16:30

Martijn Laarman · Accepted Answer · 2013-12-11 22:55:02Z

10

As the documentation on NEST and writing queries mentions you can toggle Strict() mode to trigger exceptions if a part of your query turns out to be conditionless but if thats what you really wanted then you were stuck as you've found out.

I just committed a .Verbatim() construct which works exactly like .Strict() but instead of throwing an exception it will take the query as is and render it as specified.

(f => f
    .Verbatim()
    .Term("target", "")
);

Should thus disable the conditionless query rewrite and insert the query literally as specified.

This will make it in the next version of NEST (so after the current version of 0.12.0.0)

answered Dec 11, 2013 at 22:55

Martijn Laarman

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Comments

andrew.fox · Accepted Answer · 2016-11-16 17:58:35Z

3

I will just remark that you have to use Verbatim() on every query, not just once on the top.

var searchResults = this.Client.Search<Project>(s => s
    .Query(q => q
        //.Verbatim() // no, here won't work
        .Bool(b => b
            .Should(
                bs => bs.Match(p => p.Query("hello").Field("name").Verbatim()),
                bs => bs.Match(p => p.Query("world").Field("name").Verbatim())
            )
        )
    )
);

answered Nov 16, 2016 at 17:58

andrew.fox

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