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Hybrid search with pre-filtering

Introduced 3.0

You can perform pre-filtering on hybrid search results by providing a top-level filter parameter in the hybrid query.

The filter is applied during query execution to each subquery, so only documents that match the filter are scored. Pre-filtering is useful for applying the same filter to all subqueries without duplicating it in each one.

The filter must be a single query object.

To filter the final results after they have been retrieved instead of filtering each subquery during execution, use a post-filter. For more information, see Hybrid search with post-filtering.

Example

The following example request combines a match query and a knn query and applies a common filter that restricts both subqueries to the shoes category:

POST /products/_search?search_pipeline=nlp-search-pipeline
{
  "query": {
    "hybrid": {
      "filter": {
        "term": { "category": "shoes" }
      },
      "queries": [
        {
          "match": { "description": "running shoes" }
        },
        {
          "knn": {
            "embedding": {
              "vector": [1.23, 0.45, 0.67, ...],
              "k": 10
            }
          }
        }
      ]
    }
  }
}

OpenSearch applies the category: shoes filter to both the match and knn subqueries, which is equivalent to the following query that applies the filter to each subquery individually:

POST /products/_search?search_pipeline=nlp-search-pipeline
{
  "query": {
    "hybrid": {
      "queries": [
        {
          "bool": {
            "must": {
              "match": { "description": "running shoes" }
            },
            "filter": {
              "term": { "category": "shoes" }
            }
          }
        },
        {
          "knn": {
            "embedding": {
              "vector": [1.23, 0.45, 0.67, ...],
              "k": 10,
              "filter": {
                "term": { "category": "shoes" }
              }
            }
          }
        }
      ]
    }
  }
}

Filtering on multiple conditions

Because the filter must be a single query object, combine multiple conditions using a Boolean query. The following example filters results to only in-stock shoes:

"filter": {
  "bool": {
    "must": [
      { "term": { "category": "shoes" }},
      { "term": { "in_stock": true }}
    ]
  }
}

Combining a common filter with subquery filters

A subquery can define its own filter in addition to the common filter. In this case, OpenSearch combines the two using a logical AND, further narrowing that subquery’s results.

In the following example, the common filter restricts all subqueries to the shoes category, while the match subquery is additionally narrowed to the nike brand:

POST /products/_search?search_pipeline=nlp-search-pipeline
{
  "query": {
    "hybrid": {
      "filter": {
        "term": { "category": "shoes" }
      },
      "queries": [
        {
          "bool": {
            "must": {
              "match": { "description": "running shoes" }
            },
            "filter": {
              "term": { "brand": "nike" }
            }
          }
        },
        {
          "knn": {
            "embedding": {
              "vector": [1.23, 0.45, 0.67, ...],
              "k": 10
            }
          }
        }
      ]
    }
  }
}

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