Filters a search to allow only selected documents from an index to be returned.
The SearchFilter object provides a way to designate which documents can be returned by a search. It is useful in situations where a text search using must be combined with a search of a database. The database search is done first, and then the results of the database search are used to limit the dtSearch search.
Search filters do not use names to identify documents because a filter may specify thousands, or hundreds of thousands, of documents, and a table of filenames would take too much memory and would take too long to check. Instead, each document is identified by (a) the index it belongs to, and (b) the document's DocId, a unique integer that is assigned to each document in an index. The docId for a document can be obtained by searching for the document by name, and then examining the document's properties in search results. It can also be obtained during indexing by using the DataSource abstract class as the base for your data source implementation.
A docId that is selected may be returned in search results. A document that is not selected will not be returned in search results, even if it otherwise satisfies the search request.
If the criteria for the SearchFilter can be expressed as one or more search requests, you can use SelectItemsBySearch to select documents in the SearchFilter.
Indexes and Index identifiers
A search filter can cover any number of indexes. To add an index to a search filter, call addIndex() with the full path to the index. The path must be expressed exactly as it will be expressed in the search job. The AddIndex() method returns an integer that is used to identify that index when selecting and de-selecting documents for the filter. (This makes the selection and de-selection functions, which may be called thousands of times, more effiicent.)
A search filter is implemented in the dtSearch Engine using a table of bit vectors, one for each index in the filter. Each bit vector has one bit for each document in its index. For example, a search filter for a single index with 1,000,000 documents would have 1,000,000 bits, or 125 kilobytes of data.
When using the dtSearch Engine API, it is essential to use the IDisposable pattern with all API objects except JobErrorInfo. Otherwise, the .NET garbage collector may take a long time to free memory used by potentially large objects such as SearchResults, resulting in memory depletion in long-running applications. In C# code, use a "using" clause with dtSearch Engine API objects, and in other code call Dispose() when you are done with an object.
Limiting searches with SearchFilters in dtSearchApiRef.chm.