在mongodb中如何计算游标迭代次数？

Question

var myCursor = db.bookshop.aggregate([]).pretty();

while (myCursor.hasNext()) {
   var x = myCursor.next();
   if(x.book)
   print(tojson(x));
};

while (myCursor.hasNext()) {
   var x = myCursor.next();
   if(x.journal)
   print(tojson(x));
};

while (myCursor.hasNext()) {
   var x = myCursor.next();
   if(x.musicCD)
   print(tojson(x));
};

while (myCursor.hasNext()) {
   var x = myCursor.next();
   if(x.magazine)
   print(tojson(x));
};

对于上面的代码，我尝试查找每本书、期刊、musicCD和杂志的数量。即每一个在我的文档中出现的次数。上面的代码能够以一种漂亮的格式返回整个文档。我如何找到每种类型的计数？(即图书数量、期刊数量、musicCD数量和杂志数量)。注意:我需要使用光标上的迭代来完成任务！

输出示例如下

number of books: 4
number of journals: 7
etc

blow是js文件(它很大)，任何想要参考它的人都可以使用它。

 db.bookshop.insert( {
    "_id":"185.3.16",
    "book": {
        "callnum":"185.3.16",
        "isbn":"1-292-06118-9",
        "title":"Database Systems",
        "authors":[
            {
                "fname":"Thomas",
                "lname":"Connolly"},
            { 
                "fname":"Carolyn",
                "lname":"Begg"}
        ],
        "publisher":"Pearson Pty Ltd",
        "year":2015,
        "price":136.99,
        "topic":"Computer Science",
        "description":"This is the 6th edition. You can register online to access the examples",
        "keywords":["Database", "XML", "Distributed"]
        }
});

db.bookshop.insert( {
    "_id":"163.24.12",
    "book": {
        "callnum":"163.24.12",
        "isbn":"1-123-456-810",
        "title":"Core Java",
        "authors":[
            {
                "fname":"Horstmann",
                "lname":"Cornell"}
        ],
        "publisher":"PH Pty Ltd",
        "year":2012,
        "price":142.90,
        "topic":"Computer Science",
        "description":"It covers JAVA programming and JAVA script",
        "keywords":["JAVA", "XML", "Script"]
    }
});

db.bookshop.insert( {
    "_id":"123.45.67",
    "book": {
        "callnum":"123.45.67",
        "isbn":"1-123-456-789",
        "title":"Algorithms",
        "authors":[
            {
                "fname":"James",
                "lname":"Bond"},
            {
                "fname":"Harry",
                "lname":"Potter"},
            {
                "fname":"William",
                "lname":"Stallings"}
        ],
        "publisher":"Pearson Pty Ltd",
        "year":2013,
        "price":65.85,
        "topic":"Computer Science",
        "description":"It contains algorithms and their applications. You can download examples from the website"
    }
});
db.bookshop.insert( {
    "_id":"134.41.33",
    "book": {
        "callnum":"134.41.33",
        "isbn":"1-213-431-770",
        "title":"C++ Programming",
        "authors":[
            {
                "fname":"Larry",
                "lname":"Peterson"}
        ],
        "publisher":"Pearson Pty Ltd",
        "year":2010,
        "price":74.90,
        "topic":"Computer Science",
        "description":"C++ programming and its applications",
        "keywords":["C++", "Class", "Overloading", "Inheritance"]
    }
});

db.bookshop.insert( {
    "_id":"214.56.82 12.23",
    "journal": {
        "callnum":"214.56.82",
        "issn":"S-11-123-123-456",
        "title":"Handyman",
        "vol":12,
        "issue":23,
        "price":9.85,
        "year":2017,
        "month":"February"
    }
});

db.bookshop.insert( {
    "_id":"214.56.82 12.24",
    "journal": {
        "callnum":"214.56.82",
        "issn":"S-11-123-123-456",
        "title":"Handyman",
        "vol":12,
        "issue":24,
        "price":9.85,
        "year":2017,
        "month":"August"
    }
});


db.bookshop.insert( {
    "_id":"214.56.82 12.25",
    "journal": {
        "callnum":"214.56.82",
        "issn":"S-11-123-123-456",
        "title":"Handyman",
        "vol":12,
        "issue":25,
        "price":9.85,
        "year":2017,
        "month":"October"
    }
});

db.bookshop.insert( {
    "_id":"263.18.37 5.33",
    "journal": {
        "callnum":"263.18.37",
        "issn":"D-10-123-124-456",
        "title":"Information processing",
        "vol":5,
        "issue":33,
        "price":15.90,
        "year":2018,
        "month":"January"
    }
});

db.bookshop.insert( {
    "_id":"263.18.37 5.34",
    "journal": {
        "callnum":"263.18.37",
        "issn":"D-10-123-124-456",
        "title":"Information processing",
        "vol":5,
        "issue":34,
        "price":15.90,
        "year":2018,
        "month":"May"
    }
});

db.bookshop.insert( {
    "_id":"285.32.74 17.65",
    "journal": {
        "callnum":"285.32.74",
        "issn":"C-9-123-456-666",
        "title":"Mathmetics and Computing",
        "vol":17,
        "issue":65,
        "price":35.90,
        "year":2018,
        "month":"December"
    }
});

db.bookshop.insert( {
    "_id":"285.32.74 17.66",
    "journal": {
        "callnum":"285.32.74",
        "issn":"C-9-123-456-666",
        "title":"Mathmetics and Computing",
        "vol":17,
        "issue":66,
        "price":35.90,
        "year":2019,
        "month":"February"
    }
});

db.bookshop.insert( {
    "_id":"321.12.76",
    "musicCD": {
        "callnum":"321.12.76",
        "title":"Music",
        "producer":"ABC Pty Ltd",
        "year":2010,
        "category":"Pop",
        "price":12.80
    }
});

db.bookshop.insert( {
    "_id":"342.22.42",
    "musicCD": {
        "callnum":"342.22.42",
        "title":"Stars",
        "producer":"BBC Pty Ltd",
        "year":2012,
        "category":"Classic",
        "price":12.80
    }
});

db.bookshop.insert( {
    "_id":"332.17.25",
    "musicCD": {
        "callnum":"332.17.25",
        "title":"Wiggle Wiggle",
        "producer":"Wiggle Pty Ltd",
        "year":2005,
        "category":"Kids",
        "price":10.50
    }
});

db.bookshop.insert( {
    "_id":"402.12.1",
    "magazine": {
        "callnum":"402.12.1",
        "title":"ORACLE",
        "publisher":"Julia McVeigh",
        "topic":"Database",
        "price":4.50,
        "year":2017,
        "month":"June",
        "contents":[
            {"event":[{"current":{"page":14}}, {"upcoming":{"page":15}}]},
            {"columns":[
                {"title":"Getting good service", "page":17, "author":"Jeff Spicer"},
                {"title":"Behind Unbreakable", "page":19, "author":"Ken Jacobs"},
                {"title":"Getting good", "page":21, "author":"Rich Niemiec"},
                {"title":"Building and using portals", "page":25, "author":"Robert Hall"},
                {"title":"Blocks, messages, rows", "page":29, "author":"Tom Kyte"}
            ]},
            {"upfront":{
                "Oracle monitor":{
                    "page":39,
                    "titles":["JDeveloper arrives", "Oracle and network", "Supply chain goes with flow"]
                }, 
                "Did you know":{"page":40}, 
                "Share pool":{
                    "page":53,
                    "titles":["Systems expands content-management", "ArtinSoft automates migration to Java"]
                }
            } }
        ]
    }
});

db.bookshop.insert( {
    "_id":"402.12.2",
    "magazine": {
        "callnum":"402.12.2",
        "title":"ORACLE",
        "publisher":"Julia McVeigh",
        "topic":"Database",
        "price":4.50,
        "year":2019,
        "month":"July",
        "contents":[
            {"event":[{"current":{"page":9}}, {"upcoming":{"page":10}}]},
            {"columns":[
                {"title":"Making integration", "page":15, "author":"Jeff Spicer"},
                {"title":"Oracle retrospective", "page":21, "author":"Rich Niemiec"},
                {"title":"Stretching the Web", "page":27, "author":"Robert Hall"},
                {"title":"Beyond Init.ora and SYS", "page":29, "author":"Tom Kyte"}
            ]},
            {"upfront":{
                "Oracle monitor":{
                    "page":39,
                    "titles":["Oracle information architecture", "Certifications debut at OpenWorld", "Big new for small business", "V-business on the horizon"]
                }, 
                "Did you know":{"page":40}, 
                "Share pool":{
                    "page":47,
                    "titles":["Luminate. Net intelligent database management", "Unicenter supports Oracle", "SDA's Web database objects"]
                }
            } }
        ]
    }
});

Answer 1

您可以在cursor上进行一次迭代:如果字段(book、musicCD等)被认为是为了计数，我知道这是你要找的。

var cursor = db.bookshop.find(); //find will give the cursor as well
var bookCount = 0;
var journalCount = 0;
var musicCDCount = 0;
var magazineCount = 0;
while (cursor.hasNext()) {
  var current = cursor.next();
  if (typeof current["book"] !== "undefined") {
    bookCount++;
  }

  if (typeof current["journal"] !== "undefined") {
    journalCount++;
  }

  if (typeof current["musicCD"] !== "undefined") {
    musicCDCount++;
  }

  if (typeof current["magazine"] !== "undefined") {
    magazineCount++;
  }
}
print("number of books: " + bookCount);
print("number of journals: " + journalCount);
print("number of musicCDs: " + musicCDCount);
print("number of magazines: " + magazineCount);