mongoDB聚集问题无法解决

Question

我正在查找ISBN、书名和至少有两位作者的图书出版商以及最多三位作者。我是这样写的，但在这个集合中，BOOK是一个数组，那么书中的作者也是一个数组——这对我来说有点复杂

db.Subject.aggregate([
{$unwind:{path:"$subject.book",preserveNullAndEmptyArrays: true}},
{$unwind:{path:"$subject.book.author",preserveNullAndEmptyArrays: true}},
{$group:{_id:{title:"$subject.book.bookTitle",
author:"$subject.book.author",publisher:"$subject.book.publisher",
Isbn:"$suject.book.ISBN"},counts:{$sum:1}}},
{$match:{$or:[{counts:{$eq:2}},{counts:{$eq:3}}]}}
])

但是作者和书的输出不正确，我不知道我的代码的哪一部分有错误，请帮助我，谢谢下面是主题集合的json文档

db.Subject.insert(
{
"_id":ObjectId(),
"subject": {
"subCode":"CSCI103",
"subTitle":"Algorithm and Problem Solving",
"credit":3,
"type":"Core",
"assessments": [
{ "assessNum": 1,
"weight":10,
"assessType":"Assignment",
"description":"Problem Solving and Invariant" },
{ "assessNum": 2,
"weight":10,
"assessType":"Assignment",
"description":"Assignment 1 - Sorting and Seaarching, Linked Lists, and Stack and Queues" },
{ "assessNum": 3,
"weight":10,
"assessType":"Assignment",
"description":"Assignment 2 - Recursion, Trees, and Algorithmic Strategies" },
{ "assessNum": 4,
"weight":10,
"assessType":"Test/Quiz",
"description":"Closed-book Class Test" },
{ "assessNum": 5,
"weight":60,
"assessType":"Examination",
"description": "Closed-book Final Examination" }
],
"book": [
{ "ISBN":"13:978-0-13-231681-1",
"bookType":"textbook",
"bookTitle":"Introduction to the Design and Analysis of Algorithms",
"edition":3,
"yearPub":2012,
"publisher":"Pearson",
"author": [ "Anany Levitin" ] },
{ "ISBN":"13:978-0-13-231681-1",
"bookType":"reference",
"edition":3,
"yearPub":2005,
"publisher":"Pearson",
"author": [ "B A Forouzan", "D S Malik", "M K Sen Thomson" ] }
]
}
}
)
db.Subject.insert(
{
"_id":ObjectId(),
"subject": {
"subCode":"CSCI114",
"subTitle":"Procedural Programming",
"credit":3,
"type":"Core",
"assessments": [
{ "assessNum": 1,
"weight":5,
"assessType":"Assignment",
"description":"Assignment 1 - Basic Concepts: Sequential Designs" },
{ "assignNum": 2,
"weight":5,
"assessType":"Assignment",
"description":"Assignment 2 - Control structures: Selection Designs" },
{ "assessNum": 3,
"weight":5,
"assessType":"Assignment",
"description":"Assignment 3 - Repetition Designs and Functions I" },
{ "assessNum": 4,
"weight":15,
"assessType":"Test/Quiz",
"description":"Closed-book Class Test" },
{ "assessNum": 5,
"weight": 10,
"assessType":"Test/Quiz",
"description":"Laboratory Test" },
{ "assessNum": 6,
"weight": 10,
"assessType":"Test/Quiz",
"description": "Closed-book Class Test" },
{ "assessNum": 7,
"weight":50,
"assessType":"Examination",
"description": "Closed-book Final Examination" }
],
"book": [
{ "ISBN":"13:978-1-133-52635-3",
"bookType":"reference",
"bookTitle":"C++ Programming - Program design including data structure",
"edition":6,
"yearPub":2013,
"publisher":"CENGAGE Learning",
"author": [ "Malik D S" ] },
{ "ISBN":"13:978-0-273-75983-6",
"bookType":"reference",
"bookTitle":"Starting Out With C++: From Control Structures through Objects",
"edition":7,
"yearPub":2012,
"publisher":"Addison-Wesley",
"author": [ "Tony Gaddis" ] },
]
}
}
)
db.Subject.insert(
{
"_id":ObjectId(),
"subject": {
"subCode":"CSCI124",
"subTitle":"Applied Programming",
"credit":3,
"type":"Core",
"prerequisite": ["csci114"],
"assessments": [
{ "assessNum": 1,
"weight":12,
"assessType":"Assignment",
"description":"Assignment 1 - Application on binary file processing" },
{ "assignNum": 2,
"weight":12,
"assessType":"Assignment",
"description":"Assignment 2 - Application on pointers" },
{ "assessNum": 3,
"weight":12,
"assessType":"Assignment",
"description":"Assignment 3 - Application on classes and objects and dynamic data structures" },
{ "assessNum": 4,
"weight":14,
"assessType":"Laboratory",
"description":"Laboraory/Implementation Tasks" },
{ "assessNum": 5,
"weight": 50,
"assessType":"Examination",
"description":"Closed-book Final Examination" }
],
"book": [
{ "ISBN":"10:1-4390-4023-0",
"bookType":"textbook",
"bookTitle":"Data Structures Using C++",
"edition":2,
"yearPub":2010,
"publisher":"CENGAGE Learning",
"author": [ "Malik D S" ] },
{ "ISBN":"13:978-1-133-52635-3",
"bookType":"reference",
"bookTitle":"C++ Programming - Program design including data structure",
"edition":6,
"yearPub":2013,
"publisher":"CENGAGE Learning",
"author": [ "Malik D S" ] },
{ "ISBN":"13:978-0-273-75983-6",
"bookType":"reference",
"bookTitle":"Starting Out With C++: From Control Structures through Objects",
"edition":7,
"yearPub":2012,
"publisher":"Addison-Wesley",
"author": [ "Tony Gaddis" ] }
]
}
}
)
db.Subject.insert(
{ 
"_id":ObjectId(),
"subject":{ 
"subCode":"CSCI235",
"subTitle":"Database Systems",
"credit":3,
"type":"Core",
"prerequisite": ["csci124","csci103"],
"assessments": [
{ "assessNum": 1,
"weight":10,
"assessType":"Assignment",
"description":"Assignment 1 - Normalization and Indexing" },
{ "assignNum": 2,
"weight":10,
"assessType":"Assignment",
"description":"Assignment 2 - PL/SQL programming and Concurrency Control" },
{ "assessNum": 3,
"weight":10,
"assessType":"Assignment",
"description":"Assignment 3 - JSON/BSON and MongoDB" },
{ "assessNum": 4,
"weight":10,
"assessType":"Laboratory",
"description":"Laboraory/Implementation Tasks" },
{ "assessNum": 5,
"weight": 60,
"assessType":"Examination",
"description":"Closed-book Final Examination" }
],
"book": [
{ "ISBN":"13:978-0-136-08620-8",
"bookType":"textbook",
"bookTitle":"Fundamentals of Database Systems",
"edition":6,
"yearPub":2010,
"publisher":"Addison-Wesley",
"author": [ "Ramez Elmasri", "Shamkant B Navathe" ] },
{ "ISBN":"0-07-246563-8",
"bookType":"reference",
"bookTitle":"Database Management Systems",
"edition":3,
"yearPub":2003,
"publisher":"McGraw-Hill",
"author": [ "Raghur Ramakrishnan", "Johannes Gehrke" ] } ]
}
}
)
db.Subject.insert(
{ 
"_id":ObjectId(),
"subject":{ 
"subCode":"CSCI203",
"subTitle":"Algorithm and Data Structures",
"credit":3,
"type":"Core",
"prerequisite": ["csci103"],
"assessments": [
{ "assessNum": 1,
"weight":10,
"assessType":"Assignment",
"description":"Assignment 1 - Mathematic Concepts and Algorithm Complexity" },
{ "assignNum": 2,
"weight":15,
"assessType":"Assignment",
"description":"Assignment 2 - Linear and Non-linear Data Structure" },
{ "assessNum": 3,
"weight":15,
"assessType":"Assignment",
"description":"Assignment 3 - Greedy Algorithm and Branch-and-Bound" },
{ "assessNum": 4,
"weight": 60,
"assessType":"Examination",
"description":"Closed-book Final Examination" }
],
"book": [
{ "ISBN":"13:978-0-13-231681-1",
"bookType":"textbook",
"bookTitle":"Introduction to the Design and Analysis of Algorithms",
"edition":3,
"yearPub":2012,
"publisher":"Pearson",
"author": [ "Levitin" ] },
{ "ISBN":"978-0-262-53305-8",
"bookType":"reference",
"bookTitle":"Introduction to Algorithms",
"edition":3,
"yearPub":2013,
"publisher":"The MIT Press",
"author": [ "Thomas H Cormen", "Charles E Leiserson", "Ronald L Riverst", "Clifford Stein" ] } ]
}
}
)
db.Subject.insert(
{ 
"_id":ObjectId(),
"subject":{ 
"subCode":"IACT201",
"subTitle":"Professional Practice and Ethics",
"credit":3,
"type":"Elective",
"assessments": [
{ "assessNum": 1,
"weight":35,
"assessType":"Assignment",
"description":"Assignment 1 - Ethical Dilemma Case Study" },
{ "assignNum": 2,
"weight":25,
"assessType":"Presentation",
"description":"Presentation of Case Study" },
{ "assessNum": 3,
"weight": 40,
"assessType":"Examination",
"description":"Closed-book Final Examination" }
]
}
}
)
db.Subject.insert(
{ 
"_id":ObjectId(),
"subject":{ 
"subCode":"CSCI321",
"subTitle":"Final Year Project",
"credit":6,
"type":"Core",
"assessments": [
{ "assessNum": 1,
"weight":30,
"assessType":"Presentation",
"description":"Prototype demonstration" },
{ "assignNum": 2,
"weight":70,
"assessType":"Implementation and Presentation",
"description":"Final product Presentation and assessment of product implementation by panel of project supervisors" }
]
}
}
)

Answer 1

您可以简单地用$filter编写它。但如果你发布你的预期输出，那将是更好的

db.collection.aggregate([
{
$addFields: {
"subject.book": {
$filter: {
input: "$subject.book",
cond: {
$or: [
{ $eq: [ { $size: "$$this.author" }, 2 ] },
{ $eq: [ { $size: "$$this.author" }, 3 ] }
]
}
}
}
}
}
])

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