Function HandleDensify

pg_documentdb/src/aggregation/bson_densify.c:488–631

* Aggregation pipleine stage handler for `$densify`. * Converts to a window function which densifies the incoming documents based on the mode inline * which are later unwinded using bson_lookup_unwind. * * The query returned is of the form: * if densify_spec is: * {"partitionByFields": ["a"], "field": "b", "range": {"bounds": [10, 15], "step": 1 }} * SELECT bson_lookup_unwind(stage2.doc

 * for this we use a non window function `bson_densify_range_emptytable`
 */
Query *
HandleDensify(const bson_value_t *existingValue, Query *query,
			  AggregationPipelineBuildContext *context)
{
	ReportFeatureUsage(FEATURE_STAGE_DENSIFY);

	if (existingValue->value_type != BSON_TYPE_DOCUMENT)
	{
		ereport(ERROR, (errcode(ERRCODE_DOCUMENTDB_FAILEDTOPARSE),
						errmsg(
							"The $densify stage specification must be provided as an object, but encountered %s instead",
							BsonTypeName(existingValue->value_type)),
						errdetail_log(
							"The $densify stage specification must be provided as an object, but encountered %s instead",
							BsonTypeName(existingValue->value_type))));
	}

	RangeTblEntry *rte = linitial(query->rtable);

	bool isCollectionDataTable = rte->rtekind == RTE_RELATION;

	pgbson *densifySpec = PgbsonInitFromDocumentBsonValue(existingValue);
	Const *densifySpecConst = MakeBsonConst(densifySpec);

	DensifyArguments arguments;
	memset(&arguments, 0, sizeof(DensifyArguments));
	PopulateDensifyArgs(&arguments, densifySpec);

	/*
	 * Special case for range mode densify.
	 * Generate documents in the range even when the collection is
	 * - Non existing.
	 * - Empty collection.
	 * - Filtered documents are 0.
	 *
	 * Convert base query to ... UNION ALL SELECT NULL, to add a NULL row
	 * at the end which will help generate the docs in the range.
	 *
	 * This is done due to the fact that projectors are not called
	 * if there are no rows.
	 */
	if (arguments.densifyType == DENSIFY_TYPE_RANGE)
	{
		query = GenerateUnionAllWithSelectNullQuery(query, context);

		/* We create union all query now its not a data table alone anymore */
		isCollectionDataTable = false;
	}

	if (!isCollectionDataTable)
	{
		query = MigrateQueryToSubQuery(query, context);
	}

	TargetEntry *firstEntry = linitial(query->targetList);
	Expr *docExpr = (Expr *) firstEntry->expr;

	Expr *partitionByFieldsExpr = NULL;