Function BsonLookUpProject

pg_documentdb/src/aggregation/bson_project.c:1990–2055

* $lookup semantics: For each document from a collection d1, find all documents from a * collection t2, where t1.localField = t2.foreignField. * * After the matching is done bson_dollar_lookup_project() formats the output appropriately. * * Input to the method: * 1. A document from the t1 * 2. Number of matched douments from t2 * 3. An array of matched documents from t2. *

 *
 */
static pgbson *
BsonLookUpProject(pgbson *sourceDocument, int numMatched, Datum *matchedDocument,
				  bool *matchedNulls, char *matchedDocsFieldName)
{
	/*
	 *  Creating an addField spec of the form
	 *
	 *  "asFieldname"
	 *      matchedArray[0] -> matchedArray[1] -> ..... -> matchedArray[n]
	 *
	 */
	BsonIntermediatePathNode *root = MakeRootNode();
	StringView matchedDocsView = CreateStringViewFromString(matchedDocsFieldName);

	bool treatLeafDataAsConstant = true;
	ParseAggregationExpressionContext ignoreContext = { 0 };
	BsonLeafArrayWithFieldPathNode *matchedDocsNode =
		TraverseDottedPathAndAddLeafArrayNode(
			&matchedDocsView,
			root,
			BsonDefaultCreateIntermediateNode,
			treatLeafDataAsConstant);

	int matchedIndex = 0;
	for (int i = 0; i < numMatched; i++)
	{
		/* Skip NULL elements that can arise from LEFT JOIN with no match */
		if (matchedNulls[i])
		{
			continue;
		}

		bson_value_t documentBsonValue = ConvertPgbsonToBsonValue(
			(pgbson *) matchedDocument[i]);

		const char *relativePath = NULL;
		AddValueNodeToLeafArrayWithField(matchedDocsNode, relativePath,
										 matchedIndex,
										 &documentBsonValue,
										 BsonDefaultCreateLeafNode,
										 treatLeafDataAsConstant,
										 &ignoreContext);
		matchedIndex++;
	}


	/* Executing the addFieldSpec and returning the pgbson */
	pgbson_writer writer;
	bson_iter_t documentIterator;
	PgbsonWriterInit(&writer);
	PgbsonInitIterator(sourceDocument, &documentIterator);
	bool projectNonMatchingField = true;
	ProjectDocumentState projectDocState = {
		.isPositionalAlreadyEvaluated = false,
		.parentDocument = sourceDocument,
		.topLevelPendingProjectionState = NULL,
		.skipIntermediateArrayFields = false,
	};