text_expansion queries return results for specified text fields

[kderusso]

Elasticsearch Version

8.15.3

Installed Plugins

No response

Java Version

bundled

OS Version

Cloud

Problem Description

Running a text_expansion query against a field that is not sparse_vector or rank_features returns results, when it should not. This only happens on text_expansion and not sparse_vector queries.

See the following script:

PUT _inference/sparse_embedding/my-elser-model
{
  "service": "elser",
  "service_settings": {
    "num_allocations": 1,
    "num_threads": 1
  }
}

GET _inference/sparse_embedding/my-elser-model

PUT my-test-index
{
  "mappings": {
    "properties": {
      "my_text_field": {
        "type": "text"
      },
      "my_vector_field": {
        "type": "sparse_vector"
      }
    }
  }
}

POST /_ml/trained_models/.elser_model_2_linux-x86_64/_infer
{
  "docs":[{"text_field": "Happy Halloween"}]
}


PUT my-test-index/_doc/1
{
  "my_text_field": "Happy Halloween",
  "my_vector_field": {
    "halloween": 2.7842348,
    "happy": 2.5733197,
    "horror": 0.8652177,
    "holiday": 0.85693324,
    "scare": 0.7672729,
    "christmas": 0.6851733,
    "festival": 0.6763591,
    "fear": 0.6434108,
    "zombie": 0.6021877,
    "spirit": 0.5376576,
    "october": 0.46978226,
    "birthday": 0.44018516,
    "scary": 0.36408967,
    "haunted": 0.3599118,
    "funeral": 0.3351968,
    "monster": 0.31106675,
    "joke": 0.2926158,
    "boo": 0.2861689,
    "costume": 0.27760586,
    "grin": 0.24734442,
    "batman": 0.22178747,
    "ritual": 0.22164688,
    "skull": 0.19528879,
    "sympathy": 0.1890748,
    "pumpkin": 0.18315344,
    "fun": 0.1805031,
    "humor": 0.17760311,
    "death": 0.15597177,
    "eve": 0.11133687,
    "!": 0.09539104,
    "cartoon": 0.09466279,
    "surprise": 0.06276361,
    "movie": 0.058513653,
    "grave": 0.058063928,
    "halle": 0.039445546,
    "cursed": 0.037154045,
    "dance": 0.014831517
  }
}


// Returns a result as expected
POST my-test-index/_search
{
  "query": {
    "text_expansion": {
      "my_vector_field": {
        "model_id": ".elser_model_2_linux-x86_64",
        "model_text": "happy"
      }
    }
  }
}

// Should not return results but does
GET my-test-index/_search
{
  "query": {
    "text_expansion": {
      "my_text_field": {
        "model_id": ".elser_model_2_linux-x86_64",
        "model_text": "happy"
      }
    }
  }
}

// Returns a result 
POST my-test-index/_search
{
  "query": {
    "sparse_vector": {
      "field": "my_vector_field",
      "inference_id": "my-elser-model",
      "query": "happy"
    }
  }
}

// Errors on mapping type (expected behavior)
POST my-test-index/_search
{
  "query": {
    "sparse_vector": {
      "field": "my_text_field",
      "inference_id": "my-elser-model",
      "query": "happy"
    }
  }
}

Steps to Reproduce

See attached script.

Logs (if relevant)

No response

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