[sergio-bobillier]

Add QueryBuilder#intersection to combine two queries with a boolean must clause, equivalent to AND, while retaining the existing merge behavior for other builder options. Cover empty and non-empty query combinations, and document the method.

This behavior is desired when combining query clauses that involve one or more should subclauses. Combining the following two queries with the #merge method:

{
  "bool": {
    "must": [
      { "range": { "timestamp": { "gte": "now-1d/d" } } }
    ]
  }
}

{
  "bool": {
    "should": [
      { "term": { "field": "value" } },
      { "term": { "another_field": "another_value" } }
    ]
  }
}

The resulting query is:

{
  "bool": {
    "must": [
      { "range": { "timestamp": { "gte": "now-1d/d" } } }
    ],
    "should": [
      { "term": { "field": "value" } },
      { "term": { "another_field": "another_value" } }
    ]
  }
}

Because of the way should behaves when paired with must, the results produced by this query might not be what one expects. From the Elasticsearch documentation:

Matches in the should clauses are optional. They will only boost the relevance scores of documents that already match the required must criteria and don't add new documents to the result set.

So, in the above example, the query will basically match all documents whose timestamp is within the last day. If they happen to match the should clauses, it will boost their relevance scores. However, one might actually want to get only the documents that are within the last day and also match either of the clauses inside should.

For that, the QueryBuilder#intersection method can be used to combine the queries with a must clause, ensuring that only documents matching both conditions are returned. The resulting query from doing that would be:

{
  "bool": {
    "must": [
      {
        "bool": {
          "must": [
            { "range": { "timestamp": { "gte": "now-1d/d" } } }
          ]
        }
      },
      {
        "bool": {
          "should": [
            { "term": { "field": "value" } },
            { "term": { "another_field": "another_value" } }
          ]
        }
      }
    ]
  }
}

Which produces the intended result set.

[Zauze]

Would be great to have some test cases to test union and intersection operations combined in a more sophisticated AND/OR clause

[sergio-bobillier]

Thanks. I have added an integration test with such a case, it also servers as an illustration of one of those cases when one might want an explicit intersection instead of a regular merge.