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[[query-dsl-exists-filter]]
=== Exists Filter
Returns documents that have at least one non-`null` value in the original field:
[source,js]
--------------------------------------------------
{
"constant_score" : {
"filter" : {
"exists" : { "field" : "user" }
}
}
}
--------------------------------------------------
For instance, these documents would all match the above filter:
[source,js]
--------------------------------------------------
{ "user": "jane" }
{ "user": "" } <1>
{ "user": "-" } <2>
{ "user": ["jane"] }
{ "user": ["jane", null ] } <3>
--------------------------------------------------
<1> An empty string is a non-`null` value.
<2> Even though the `standard` analyzer would emit zero tokens, the original field is non-`null`.
<3> At least one non-`null` value is required.
These documents would *not* match the above filter:
[source,js]
--------------------------------------------------
{ "user": null }
{ "user": [] } <1>
{ "user": [null] } <2>
{ "foo": "bar" } <3>
--------------------------------------------------
<1> This field has no values.
<2> At least one non-`null` value is required.
<3> The `user` field is missing completely.
[float]
==== `null_value` mapping
If the field mapping includes the `null_value` setting (see <<mapping-core-types>>)
then explicit `null` values are replaced with the specified `null_value`. For
instance, if the `user` field were mapped as follows:
[source,js]
--------------------------------------------------
"user": {
"type": "string",
"null_value": "_null_"
}
--------------------------------------------------
then explicit `null` values would be indexed as the string `_null_`, and the
following docs would match the `exists` filter:
[source,js]
--------------------------------------------------
{ "user": null }
{ "user": [null] }
--------------------------------------------------
However, these docs--without explicit `null` values--would still have
no values in the `user` field and thus would not match the `exists` filter:
[source,js]
--------------------------------------------------
{ "user": [] }
{ "foo": "bar" }
--------------------------------------------------
[float]
==== Caching
The result of the filter is always cached.
|
