Retrieve selected fields from a searchedit

By default, each hit in the search response includes the document _source, which is the entire JSON object that was provided when indexing the document. If you only need certain source fields in the search response, you can use the source filtering to restrict what parts of the source are returned.

Returning fields using only the document source has some limitations:

  • The _source field does not include multi-fields or field aliases. Likewise, a field in the source does not contain values copied using the copy_to mapping parameter.
  • Since the _source is stored as a single field in Lucene, the whole source object must be loaded and parsed, even if only a small number of fields are needed.

To avoid these limitations, you can:

  • Use the docvalue_fields parameter to get values for selected fields. This can be a good choice when returning a fairly small number of fields that support doc values, such as keywords and dates.
  • Use the stored_fields parameter to get the values for specific stored fields. (Fields that use the store mapping option.)

If needed, you can use the script_field parameter to transform field values in the response using a script. However, scripts can’t make use of Elasticsearch’s index structures or related optimizations. This can sometimes result in slower search speeds.

You can find more detailed information on each of these methods in the following sections:

Source filteringedit

You can use the _source parameter to select what fields of the source are returned. This is called source filtering.

The following search API request sets the _source request body parameter to false. The document source is not included in the response.

GET /_search
{
  "_source": false,
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  }
}

To return only a subset of source fields, specify a wildcard (*) pattern in the _source parameter. The following search API request returns the source for only the obj field and its properties.

GET /_search
{
  "_source": "obj.*",
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  }
}

You can also specify an array of wildcard patterns in the _source field. The following search API request returns the source for only the obj1 and obj2 fields and their properties.

GET /_search
{
  "_source": [ "obj1.*", "obj2.*" ],
  "query": {
    "match": {
      "user.id": "kimchy"
    }
  }
}

For finer control, you can specify an object containing arrays of includes and excludes patterns in the _source parameter.

The fields parameter handles field types like field aliases and constant_keyword whose values aren’t always present in the _source. Other mapping options are also respected, including ignore_above, ignore_malformed and null_value.

If the includes property is not specified, the entire document source is returned, excluding any fields that match a pattern in the excludes property.

The following search API request returns the source for only the obj1 and obj2 fields and their properties, excluding any child description fields.

GET /_search
{
  "_source": {
    "includes": [ "obj1.*", "obj2.*" ],
    "excludes": [ "*.description" ]
  },
  "query": {
    "term": {
      "user.id": "kimchy"
    }
  }
}

Doc value fieldsedit

You can use the docvalue_fields parameter to return doc values for one or more fields in the search response.

Doc values store the same values as the _source but in an on-disk, column-based structure that’s optimized for sorting and aggregations. Since each field is stored separately, Elasticsearch only reads the field values that were requested and can avoid loading the whole document _source.

Doc values are stored for supported fields by default. However, doc values are not supported for text or text_annotated fields.

The following search request uses the docvalue_fields parameter to retrieve doc values for the following fields:

  • Fields with names starting with my_ip
  • my_keyword_field
  • Fields with names ending with _date_field
GET /_search
{
  "query": {
    "match_all": {}
  },
  "docvalue_fields": [
    "my_ip*",                     
    {
      "field": "my_keyword_field" 
    },
    {
      "field": "*_date_field",
      "format": "epoch_millis"    
    }
  ]
}

Wildcard patten used to match field names, specified as a string.

Wildcard patten used to match field names, specified as an object.

With the object notation, you can use the format parameter to specify a format for the field’s returned doc values. Date fields support a date format. Numeric fields support a DecimalFormat pattern. Other field data types do not support the format parameter.

You cannot use the docvalue_fields parameter to retrieve doc values for nested objects. If you specify a nested object, the search returns an empty array ([ ]) for the field. To access nested fields, use the inner_hits parameter’s docvalue_fields property.

Stored fieldsedit

It’s also possible to store an individual field’s values by using the store mapping option. You can use the stored_fields parameter to include these stored values in the search response.

The stored_fields parameter is for fields that are explicitly marked as stored in the mapping, which is off by default and generally not recommended. Use source filtering instead to select subsets of the original source document to be returned.

Allows to selectively load specific stored fields for each document represented by a search hit.

GET /_search
{
  "stored_fields" : ["user", "postDate"],
  "query" : {
    "term" : { "user" : "kimchy" }
  }
}

* can be used to load all stored fields from the document.

An empty array will cause only the _id and _type for each hit to be returned, for example:

GET /_search
{
  "stored_fields" : [],
  "query" : {
    "term" : { "user" : "kimchy" }
  }
}

If the requested fields are not stored (store mapping set to false), they will be ignored.

Stored field values fetched from the document itself are always returned as an array. On the contrary, metadata fields like _routing are never returned as an array.

Also only leaf fields can be returned via the stored_fields option. If an object field is specified, it will be ignored.

On its own, stored_fields cannot be used to load fields in nested objects — if a field contains a nested object in its path, then no data will be returned for that stored field. To access nested fields, stored_fields must be used within an inner_hits block.

Disable stored fieldsedit

To disable the stored fields (and metadata fields) entirely use: _none_:

GET /_search
{
  "stored_fields": "_none_",
  "query" : {
    "term" : { "user" : "kimchy" }
  }
}

_source and version parameters cannot be activated if _none_ is used.

Script fieldsedit

You can use the script_fields parameter to retrieve a script evaluation (based on different fields) for each hit. For example:

GET /_search
{
  "query": {
    "match_all": {}
  },
  "script_fields": {
    "test1": {
      "script": {
        "lang": "painless",
        "source": "doc['price'].value * 2"
      }
    },
    "test2": {
      "script": {
        "lang": "painless",
        "source": "doc['price'].value * params.factor",
        "params": {
          "factor": 2.0
        }
      }
    }
  }
}

Script fields can work on fields that are not stored (price in the above case), and allow to return custom values to be returned (the evaluated value of the script).

Script fields can also access the actual _source document and extract specific elements to be returned from it by using params['_source']. Here is an example:

GET /_search
    {
        "query" : {
            "match_all": {}
        },
        "script_fields" : {
            "test1" : {
                "script" : "params['_source']['message']"
            }
        }
    }

Note the _source keyword here to navigate the json-like model.

It’s important to understand the difference between doc['my_field'].value and params['_source']['my_field']. The first, using the doc keyword, will cause the terms for that field to be loaded to memory (cached), which will result in faster execution, but more memory consumption. Also, the doc[...] notation only allows for simple valued fields (you can’t return a json object from it) and makes sense only for non-analyzed or single term based fields. However, using doc is still the recommended way to access values from the document, if at all possible, because _source must be loaded and parsed every time it’s used. Using _source is very slow.