Package org.apache.lucene.search

# Class FieldExistsQuery

java.lang.Object
org.apache.lucene.search.Query
org.apache.lucene.search.FieldExistsQuery

public class FieldExistsQuery extends Query
A `Query` that matches documents that contain either a `KnnFloatVectorField`, `KnnByteVectorField` or a field that indexes norms or doc values.

## Constructor Summary

Constructors
Constructor
Description
`FieldExistsQuery(String field)`
Create a query that will match that have a value for the given `field`.

## Method Summary

Modifier and Type
Method
Description
`Weight`
`createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)`
Expert: Constructs an appropriate Weight implementation for this query.
`boolean`
`equals(Object other)`
Override and implement query instance equivalence properly in a subclass.
`static DocIdSetIterator`
`getDocValuesDocIdSetIterator(String field, LeafReader reader)`
Returns a `DocIdSetIterator` from the given field or null if the field doesn't exist in the reader or if the reader has no doc values for the field.
`String`
`getField()`
`int`
`hashCode()`
Override and implement query hash code properly in a subclass.
`Query`
`rewrite(IndexSearcher indexSearcher)`
Expert: called to re-write queries into primitive queries.
`String`
`toString(String field)`
Prints a query to a string, with `field` assumed to be the default field and omitted.
`void`
`visit(QueryVisitor visitor)`
Recurse through the query tree, visiting any child queries.

### Methods inherited from class org.apache.lucene.search.Query

`classHash, sameClassAs, toString`

### Methods inherited from class java.lang.Object

`clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

## Constructor Details

### FieldExistsQuery

public FieldExistsQuery(String field)
Create a query that will match that have a value for the given `field`.

## Method Details

### getDocValuesDocIdSetIterator

public static DocIdSetIterator getDocValuesDocIdSetIterator(String field, LeafReader reader) throws IOException
Returns a `DocIdSetIterator` from the given field or null if the field doesn't exist in the reader or if the reader has no doc values for the field.

Throws:
  `IOException`

### getField

public String getField()

### toString

public String toString(String field)
Description copied from class: `Query`
Prints a query to a string, with `field` assumed to be the default field and omitted.

Specified by:
  `toString` in class `Query`

### visit

public void visit(QueryVisitor visitor)
Description copied from class: `Query`
Recurse through the query tree, visiting any child queries.

Specified by:
  `visit` in class `Query`
Parameters:
  `visitor` - a QueryVisitor to be called by each query in the tree

### equals

public boolean equals(Object other)
Description copied from class: `Query`
Override and implement query instance equivalence properly in a subclass. This is required so that `QueryCache` works properly.

Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical to those of the other instance. Utility methods are provided for certain repetitive code.

Specified by:
  `equals` in class `Query`
See Also:
  - `Query.sameClassAs(Object)`
  - `Query.classHash()`

### hashCode

public int hashCode()
Description copied from class: `Query`
Override and implement query hash code properly in a subclass. This is required so that `QueryCache` works properly.

Specified by:
  `hashCode` in class `Query`
See Also:
  - `Query.equals(Object)`

### rewrite

public Query rewrite(IndexSearcher indexSearcher) throws IOException
Description copied from class: `Query`
Expert: called to re-write queries into primitive queries. For example, a PrefixQuery will be rewritten into a BooleanQuery that consists of TermQuerys.

Callers are expected to call `rewrite` multiple times if necessary, until the rewritten query is the same as the original query.

The rewrite process may be able to make use of IndexSearcher's executor and be executed in parallel if the executor is provided.

Overrides:
  `rewrite` in class `Query`
Throws:
  `IOException`
See Also:
  - `IndexSearcher.rewrite(Query)`

### createWeight

public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost)
Description copied from class: `Query`
Expert: Constructs an appropriate Weight implementation for this query.

Only implemented by primitive queries, which re-write to themselves.

Overrides:
  `createWeight` in class `Query`
Parameters:
  `scoreMode` - How the produced scorers will be consumed.
  `boost` - The boost that is propagated by the parent queries.