Function bson_expression_map

pg_documentdb/src/operators/bson_expression.c:824–927

* bson_expression_map evaluates a bson expression from a given array of * document. This follows operator expressions as per aggregation expressions. * The input document should be a document containing the given field name that * points to an array of documents. * e.g. { "array": [{"_id": 1 ...}, {"_id": 2 ...}, ...]} * The expression is expected to be a single value bson document * e.g. {

 * will not match the size of the input array.
 */
Datum
bson_expression_map(PG_FUNCTION_ARGS)
{
	pgbson *document = PG_GETARG_PGBSON_PACKED(0);
	char *srcArrayName = text_to_cstring(PG_GETARG_TEXT_P(1));
	pgbson *expression = PG_GETARG_PGBSON_PACKED(2);
	bool isNullOnEmpty = PG_GETARG_BOOL(3);
	ExpressionVariableContext *variableContext = NULL;
	pgbsonelement expressionElement;
	pgbson_writer writer;
	pgbson_array_writer arrayWriter;

	AggregationExpressionData expressionData;
	memset(&expressionData, 0, sizeof(AggregationExpressionData));

	PgbsonToSinglePgbsonElement(expression, &expressionElement);
	bson_iter_t docIter;
	PgbsonInitIterator(document, &docIter);
	const bson_value_t *inputArray = NULL;

	while (bson_iter_next(&docIter))
	{
		const char *key = bson_iter_key(&docIter);
		if (strcmp(key, srcArrayName) == 0)
		{
			inputArray = bson_iter_value(&docIter);
			break;
		}
	}

	/* Missing input Array */
	if (inputArray == NULL)
	{
		ereport(ERROR, errcode(ERRCODE_INTERNAL_ERROR), errmsg(
					"Missing Input Array for bson_expression_map: '%s'", srcArrayName));
	}
	else if (inputArray->value_type != BSON_TYPE_ARRAY)
	{
		ereport(ERROR, errcode(ERRCODE_INTERNAL_ERROR), errmsg(
					"Input Array for bson_express_map of wrong type Name: '%s' Type: '%s'",
					srcArrayName, BsonTypeName(inputArray->value_type)));
	}

	/* Init AggregateExpressionData */
	const AggregationExpressionData *state;
	const int argPosition = 2;
	ParseAggregationExpressionContext context = { 0 };

	SetCachedFunctionState(
		state,
		AggregationExpressionData,
		argPosition,
		ParseAggregationExpressionData,
		&expressionElement.bsonValue,
		&context);

	if (state == NULL)
	{