Function BsonUnwindArray

pg_documentdb/src/aggregation/bson_unwind.c:255–386

* BsonUnwindArray is the internal implementation of $unwind as a set returning function * path -> The path to be unwound * indexFieldName -> optional string to add the index in the output document * preserveNullAndEmpty -> whether to keep null and empty unwind values * * PG_FUNCTION_ARGS contains the document */

 *  PG_FUNCTION_ARGS contains the document
 */
static Datum
BsonUnwindArray(PG_FUNCTION_ARGS, Tuplestorestate *tupleStore, TupleDesc *tupleDescriptor,
				char *path, char *indexFieldName, bool
				preserveNullAndEmpty)
{
	pgbson *document = PG_GETARG_PGBSON_PACKED(0);

	/* Strip the $ prefix from the path */
	if (strlen(path) <= 1)
	{
		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg(
							"$unwind path should have at least two characters")));
	}

	if (path[0] != '$')
	{
		ereport(ERROR, (errcode(ERRCODE_INVALID_PARAMETER_VALUE), errmsg(
							"$unwind path must be prefixed by $")));
	}
	path = path + 1;

	/* Start the iterator at the provided path */
	bson_iter_t documentIterator;
	if (!PgbsonInitIteratorAtPath(document, path, &documentIterator))
	{
		/* No field was found, return no results on this document */
		if (preserveNullAndEmpty)
		{
			/* undefined elements are preserved */
			bson_value_t element;
			element.value_type = BSON_TYPE_EOD;
			Datum values[1];
			bool isNull = false;

			values[0] = PointerGetDatum(BsonUnwindElement(document,
														  path,
														  indexFieldName,
														  -1,
														  &element));
			tuplestore_putvalues(tupleStore, *tupleDescriptor, values, &isNull);
		}

		PG_FREE_IF_COPY(document, 0);
		PG_RETURN_VOID();
	}

	if (!BSON_ITER_HOLDS_ARRAY(&documentIterator))
	{
		if (!BSON_ITER_HOLDS_NULL(&documentIterator))
		{
			/* Single non-null elements are always preserved */
			Datum values[1];
			bool nulls[1];

			if (indexFieldName == NULL)
			{
				/* This is just the source doc */
				values[0] = PG_GETARG_DATUM(0);