Function SelectUpdateCandidate

pg_documentdb/src/commands/update.c:3386–3611

* SelectUpdateCandidate finds at most 1 document to update, locks the row, * writes the updated value of the document to updateCandidate (if no update happened it sets it to NULL), * and returns whether a document was found. */

 * and returns whether a document was found.
 */
static bool
SelectUpdateCandidate(MongoCollection *collection, int64 shardKeyHash,
					  UpdateOneParams *updateOneParams, UpdateCandidate *updateCandidate,
					  bool getOriginalDocument, bool *hasOnlyObjectIdFilter)
{
	uint64 planId = QUERY_UPDATE_SELECT_UPDATE_CANDIDATE;
	SPI_connect();

	List *sortFieldDocuments = updateOneParams->sort != NULL ?
							   BsonValueDocumentDecomposeFields(updateOneParams->sort) :
							   NIL;
	int argCount = list_length(sortFieldDocuments);

	bool queryHasNonIdFilters = false;
	bool isIdFilterCollationAwareIgnore = false;
	pgbson *objectIdFilter =
		GetObjectIdFilterFromQueryDocumentValue(updateOneParams->query,
												&queryHasNonIdFilters,
												&isIdFilterCollationAwareIgnore);
	*hasOnlyObjectIdFilter = objectIdFilter != NULL && !queryHasNonIdFilters;

	int nextSqlArgIndex = 1;
	bool foundDocument = false;

	StringInfoData updateQuery;
	initStringInfo(&updateQuery);

	appendStringInfo(&updateQuery, "SELECT ctid, object_id, document, tableoid FROM");

	if (collection->shardTableName[0] != '\0')
	{
		appendStringInfo(&updateQuery, " %s.%s", ApiDataSchemaName,
						 collection->shardTableName);
	}
	else
	{
		appendStringInfo(&updateQuery, " %s.documents_" UINT64_FORMAT, ApiDataSchemaName,
						 collection->collectionId);
	}

	appendStringInfo(&updateQuery, " WHERE ");

	const bson_value_t *variableSpec = updateOneParams->variableSpec;
	pgbson *variableSpecBson = NULL;
	if (queryHasNonIdFilters)
	{
		variableSpecBson = variableSpec != NULL &&
						   variableSpec->value_type == BSON_TYPE_DOCUMENT ?
						   PgbsonInitFromDocumentBsonValue(variableSpec) : NULL;
	}

	bool applyVariableSpec = variableSpecBson != NULL;
	bool hasFilter = false;
	if (queryHasNonIdFilters)
	{
		if (applyVariableSpec)
		{
			planId = QUERY_UPDATE_SELECT_UPDATE_CANDIDATE_NON_OBJECT_ID_LET_AND_COLLATION;