http://info-mongodb-com.s3.amazonaws.com/ReferenceCards15-PDF.pdf

https://coggle.it/diagram/Vz9LvW8byvN0I38x

cd ..

cd ..

cd mongodb

cd homework

cd hw3-2

mvn compile exec:java -Dexec.mainClass=course.BlogController

mongoimport -d school -c students < students.json

db.students.find({ "scores" : { "$elemMatch" : { "type" : "homework"} }});

db.posts.aggregate([{$unwind:"$comments.author"},{$group:{_id:"$comments.author",total:{$sum:_id}}},{$sort:{total:1}},{$limit:{1}}])

h.w ---5-1

db.posts.aggregate([{$unwind:"$comments"},{$group:{_id:{author:"$comments.author"},total:{$sum:1}}},{$sort:{total:-1}}])

h.w 5-2

mongoimport -d test -c grades --drop homework/hw5-2/small_zips.json

Q. Please calculate the average population of cities in California (abbreviation CA) and New York (NY) (taken together) with populations over 25,000.

ANS use test

db.grades.aggregate([{$match:{ state:"CA",state:"NY",pop:{$gte:250000}}},{$group:{ _id:null,ppo:{$avg:"$pop"}}}])

hw 5- 3

mongoimport -d test -c grades --drop homework/hw5-3/grades.json

Q. Your task is to calculate the class with the best average student performance. This involves calculating an average for each student in each class of all non-quiz assessments and then averaging those numbers to get a class average. To be clear, each student's average includes only exams and homework grades. Don't include their quiz scores in the calculation.

ans

avg of each stu---- db.grades.aggregate([{$unwind:"$scores"},{$match:{ "scores.type":"homework","scores.type":"exam"}},{$group:{_id:{studentid:"$student_id",classid:"$class_id"},avg_stu:{$avg:"$scores.score"}}}])

avg of class---

db.grades.aggregate([{$unwind:"$scores"},{$match:{ "scores.type":"homework","scores.type":"exam"}},{$group:{_id:{studentid:"$student_id",classid:"$class_id"},avg_stu:{$avg:"$scores.score"}}},{$group:{_id:"$_id.classid",avg_class:{$avg:"$avg_stu"}}},{$sort:{avg_class:1}}])


db.grades.aggregate([{$unwind:"$scores"},{$match:{ "scores.type":"homework","scores.type":"exam"}},{$group:{_id:{studentid:"$student_id",classid:"$class_id"},avg_stu:{$avg:"$scores.score"}}},{$match:{class_id:"2"}}])

***FINAL EXAM

Q1 :

Q2 :
db.messages.aggregate ([ {$unwind:"$headers.To"}, {$group:{_id:{id:"$_id",from:"$headers.From"},"TO":{$addToSet:"$headers.To"}}}, {$unwind:"$TO"}, {$group:{"_id":{ sender:"$_id.from","receiver":"$TO"},total_count:{$sum:1}}}, {$sort:{total_count:-1}}, {$limit:2} ])

Q3 : db.messages.update({"headers.Message-ID":"8147308.1075851042335.JavaMail.evans@thyme"},{$addToSet:{"headers.To":"[email protected]"}})

Q4 : postsCollection.update( new BasicDBObject("permalink", permalink), new BasicDBObject("$inc",new BasicDBObject("comments."+ordinal+".num_likes",1)));

Q5 :

Q7 : MongoClient c = new MongoClient(new MongoClientURI("mongodb://localhost")); DB db = c.getDB("final7"); int i =0; DBCollection album = db.getCollection("albums"); DBCollection image = db.getCollection("images");

        DBCursor cur = image.find();
        cur.next();
        
        while (cur.hasNext()){
            Object id = cur.curr().get("_id");
           DBCursor curalbum = album.find(new BasicDBObject("images", id));
           if(!curalbum.hasNext()){
               image.remove(new BasicDBObject("_id", id));
           }
           cur.next();
        }
    }

db.albums.aggregate({$unwind:"$images"},{$group:{_id:null,sum:{$sum:"$images"},count:{$sum:1}}}

db.images.find({"tags":"sunrises"}).count()