我正在尝试根据diagnosticType和更高级别的patientKey和encounterKey聚合文档。这是文档的样子:{"_id":ObjectId("...."),"patientKey":1,"encounterKey":2,"diagnosisType":"medical_history","diagnosisCode":"Z87.81",}{"_id":ObjectId("...."),"patientKey":1,"encounterKey":2,"diagnosisType":"problem_list","diagnosisCode":"2x.2",}{"_id"