addTermPosition method
Adds or updates a posting position for the docId to PostingsMap entry
for the term.
Returns true if the posting positions for the docId did not previously
exist in the PostingsMap.
Looks up an existing entry for term and adds a position to the list of
positions for docId if it exists.
If no entry for term exists in the PostingsMap, creates a new entry
for term.
If zone is null, the posting position zone name is "null".
If no positions list exists for docId, creates a new position list
for docId.
Adds position to the positions list for docId if it is not already
in the list.
Sorts the positions list in ascending order.
Updates the term entry in the PostingsMap.
Implementation
bool addTermPosition(
{required String term,
required String docId,
required Pt position,
String? zone}) {
//
zone = zone ?? 'null';
// get the entry for the term or initialize a new one if it does not exist
final entry = this[term] ?? {};
// get the existing zone postings for [docId] if it exists
final docPostings = entry[docId] ?? {};
// get the existing psitions in the zone for [zone] if it exists
final docFieldPostings = docPostings[zone];
// initializes positions set from docFieldPostings or an empty list
final set = (docFieldPostings ?? []).toSet();
// add position to the set
set.add(position);
// convert to list
final positions = set.toList();
// order the list of positions in ascending order
positions.sort(((a, b) => a.compareTo(b)));
// set the positions for docId
docPostings[zone] = positions;
// overwrite the zone postings for docId
entry[docId] = docPostings;
// set the entry for term with the new positions for docId
this[term] = entry;
// return true if a positions list for [docId] did not existed
return docFieldPostings == null;
}