[[query-dsl-query-filter]]
=== Query Filter

Wraps any query to be used as a filter. Can be placed within queries
that accept a filter.

[source,js]
--------------------------------------------------
{
    "constantScore" : {
        "filter" : {
            "query" : { 
                "query_string" : { 
                    "query" : "this AND that OR thus"
                }
            }
        }
    }
}
--------------------------------------------------

[float]
==== Caching

The result of the filter is not cached by default. The `_cache` can be
set to `true` to cache the *result* of the filter. This is handy when
the same query is used on several (many) other queries. Note, the
process of caching the first execution is higher when not caching (since
it needs to satisfy different queries).

Setting the `_cache` element requires a different format for the
`query`:

[source,js]
--------------------------------------------------
{
    "constantScore" : {
        "filter" : {
            "fquery" : {
                "query" : { 
                    "query_string" : { 
                        "query" : "this AND that OR thus"
                    }
                },
                "_cache" : true
            }
        }
    }
}
--------------------------------------------------
