后过滤

您可以通过布尔过滤器或使用 post_filter 参数来实现后过滤。

布尔过滤器配合近似最近邻搜索

布尔过滤器由一个包含 k-NN 查询和过滤器的布尔查询构成。例如，以下查询首先搜索距离指定location最近的酒店，然后过滤结果以返回评分在 8 到 10 之间（含）且提供停车场的酒店：

POST /hotels-index/_search
{
  "size": 3,
  "query": {
    "bool": {
      "filter": {
        "bool": {
          "must": [
            {
              "range": {
                "rating": {
                  "gte": 8,
                  "lte": 10
                }
              }
            },
            {
              "term": {
                "parking": "true"
              }
            }
          ]
        }
      },
      "must": [
        {
          "knn": {
            "location": {
              "vector": [
                5,
                4
              ],
              "k": 20
            }
          }
        }
      ]
    }
  }
}

响应包含匹配酒店的文档：

{
  "took" : 95,
  "timed_out" : false,
  "_shards" : {
    "total" : 1,
    "successful" : 1,
    "skipped" : 0,
    "failed" : 0
  },
  "hits" : {
    "total" : {
      "value" : 5,
      "relation" : "eq"
    },
    "max_score" : 0.72992706,
    "hits" : [
      {
        "_index" : "hotels-index",
        "_id" : "3",
        "_score" : 0.72992706,
        "_source" : {
          "location" : [
            4.9,
            3.4
          ],
          "parking" : "true",
          "rating" : 9
        }
      },
      {
        "_index" : "hotels-index",
        "_id" : "6",
        "_score" : 0.3012048,
        "_source" : {
          "location" : [
            6.4,
            3.4
          ],
          "parking" : "true",
          "rating" : 9
        }
      },
      {
        "_index" : "hotels-index",
        "_id" : "5",
        "_score" : 0.24154587,
        "_source" : {
          "location" : [
            3.3,
            4.5
          ],
          "parking" : "true",
          "rating" : 8
        }
      }
    ]
  }
}

post_filter 参数

如果您将 knn 查询与过滤器或其他子句（例如 bool、must、match）一起使用，返回的结果可能会少于 k 个。在此示例中，post_filter 将结果数量从 2 个减少到 1 个：

GET my-knn-index-1/_search
{
  "size": 2,
  "query": {
    "knn": {
      "my_vector2": {
        "vector": [2, 3, 5, 6],
        "k": 2
      }
    }
  },
  "post_filter": {
    "range": {
      "price": {
        "gte": 5,
        "lte": 10
      }
    }
  }
}