C# Class Lucene.Net.Search.Filter

Creates a {@link DocIdSet} enumerating the documents that should be permitted in search results. NOTE: null can be returned if no documents are accepted by this Filter.

Note: This method will be called once per segment in the index during searching. The returned {@link DocIdSet} must refer to document IDs for that segment, not for the top-level reader. @param reader a {@link IndexReader} instance opened on the index currently searched on. Note, it is likely that the provided reader does not represent the whole underlying index i.e. if the index has more than one segment the given reader only represents a single segment.