Elasticsearch Multiple Prefix Keywords

Question

I need to use the prefix filter, but allow multiple different prefixes, i.e.

{"prefix": {"myColumn": ["This", "orThis", "orEvenThis"]}}

This does not work. And if I add each as a separate prefix is also obviously doesn't work.

Help is appreciated.

Update

I tried should but without any luck:

$this->dsl['body']['query']['bool']['should'] = [
    ["prefix" => ["myColumn" =>  "This"]],
    ["prefix" => ["myColumn" =>  "orThis"]]
];

When I add those two constraints, I get ALL responses (as though filter is not working). But if I use must with either of those clauses, then I do get a response back with the correct prefix.

Answer 1

Based on your comments, it sounds like it may just be an issue with the syntax. With all ES queries (just like SQL ones), I suggest starting simple and just submitting them to ES as the raw DSL outside of code (although in your case this wasn't easily doable). For the request, it's a pretty straight forward one:

{
  "query" : {
    "bool" : {
      "must" : [ ... ],
      "filter" : [
        {
          "bool" : {
            "should" : [
              {
                "prefix" : {
                  "myColumn" : "This"
                }
              },
              {
                "prefix" : {
                  "myColumn" : "orThis"
                }
              },
              {
                "prefix" : {
                  "myColumn" : "orEvenThis"
                }
              }
            ]
          }
        }
      ]
    }
  }
}

I added it as a filter because the optional nature of your prefixing is not improving relevancy: it's literally asking that one of them must match. In such cases where the question is "does this match? yes / no", then you should use a filter (with the added bonus that that's cacheable!). If you're asking "does this match, and which matches better?" then you want a query (because that's relevancy / scoring).

Note: The initial issue appeared to be that the bool / must was unmentioned and the suggestion was to just use a bool / should.

{
  "bool" : {
    "should" : [
      {
        "prefix" : {
          "myColumn" : "This"
        }
      },
      {
        "prefix" : {
          "myColumn" : "orThis"
        }
      },
      {
        "prefix" : {
          "myColumn" : "orEvenThis"
        }
      }
    ]
  }
}

behaves differently than

{
  "bool" : {
    "must" : [ ... ],
    "should" : [
      {
        "prefix" : {
          "myColumn" : "This"
        }
      },
      {
        "prefix" : {
          "myColumn" : "orThis"
        }
      },
      {
        "prefix" : {
          "myColumn" : "orEvenThis"
        }
      }
    ]
  }
}

because the must impacts the required nature of should. Without must, should behaves like a boolean OR. However, with must, it behaves as a completely optional function to improve relevancy (score). To make it go back to the boolean OR behavior with must, you must add minimum_should_match to the bool compound query.

{
  "bool" : {
    "must" : [ ... ],
    "should" : [
      {
        "prefix" : {
          "myColumn" : "This"
        }
      },
      {
        "prefix" : {
          "myColumn" : "orThis"
        }
      },
      {
        "prefix" : {
          "myColumn" : "orEvenThis"
        }
      }
    ],
    "minimum_should_match" : 1
  }
}

Notice that it's a component of the bool query, and not of either should or must!