Retrieve selected fields from a search
editRetrieve selected fields from a search
editBy 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 thecopy_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 thestore
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 filtering
editYou 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.
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 fields
editYou 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 |
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 fields
editIt’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 fields
editTo disable the stored fields (and metadata fields) entirely use: _none_
:
GET /_search { "stored_fields": "_none_", "query" : { "term" : { "user" : "kimchy" } } }
Script fields
editYou 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.