M101J: MongoDB for Java Developers

Week 1: Introduction

Following are presented the contents and answers to the HomeWorks belonging to Week 1 (Introduction) for “M101J: MongoDB for Java Developers” course offered by https://university.mongodb.com/ started at 2014-03-17.

HOMEWORK 1.1

ANSWER HOMEWORK 1.1:

Simply it was about verifying the correct MongoDB installation, example data import and basic query execution over those imported data. First, mongorestore:

$ l
dump/
$ /opt/mongodb-linux-i686-2.6.0/bin/mongorestore
connected to: 127.0.0.1
2014-05-07T11:03:39.465-0500 dump/m101/hw1.bson
2014-05-07T11:03:39.466-0500    going into namespace [m101.hw1]
1 objects found
2014-05-07T11:03:39.514-0500    Creating index: { key: { _id: 1 }, ns: "m101.hw1", name: "_id_" }
2014-05-07T11:03:39.595-0500 dump/m101/funnynumbers.bson
2014-05-07T11:03:39.595-0500    going into namespace [m101.funnynumbers]
100 objects found
2014-05-07T11:03:39.598-0500    Creating index: { key: { _id: 1 }, ns: "m101.funnynumbers", name: "_id_" }
$

Then, some MongoShell checks about the restoration and the result answer:

> show dbs
admin    (empty)
blog     0.078GB
enron    0.953GB
final7   0.078GB
local    0.078GB
school   0.078GB
test     0.078GB
weather  0.078GB
> show dbs
admin    (empty)
blog     0.078GB
enron    0.953GB
final7   0.078GB
local    0.078GB
m101     0.078GB
school   0.078GB
test     0.078GB
weather  0.078GB
> use m101
switched to db m101
> show tables
funnynumbers
hw1
system.indexes
> db.hw1.count()
1
> db.hw1.findOne()
{
    "_id" : ObjectId("50773061bf44c220307d8514"),
    "answer" : 42,
    "question" : "The Ultimate Question of Life, The Universe and Everything"
}
>

HOMEWORK 1.2

ANSWER HOMEWORK 1.2:

Simple theoretic question answered having the notion of JSON structure and syntax, see http://www.json.org/ .

• WRONG. The separator between key:value pairs is a , (comma), NOT a ; (semi-colon).
• CORRECT. It’s a valid JSON document, maybe one thing to note is that the value of the quotes key is an array, and still a valid document.
• CORRECT. The empty document IS a valid document.
• WRONG. A couple of errors and doubt interpretations here: the value of the boros key IS NOT valid, it’s not a document nor an array, to be a valid document must have key:value pairs separated by , (commas) inside enclosing { and } (curly braces) and it doesn’t, and to be a valid array must be a list of elements separated by , (commas) inside enclosing [ and ] (square brackets) and it doesn’t; further, the “population” and 7999034 items ARE NOT key NOR value NOR array elements of anything; so this “document” is all broke and wrong.
• CORRECT. This is a valid and fairly common nested document mixing both objects and arrays.

HOMEWORK 1.3

ANSWER HOMEWORK 1.3:

Like HW 1.1, it was about verifying the correct MongoDB installation and example data import, furthermore installation and correctness of JDK, Maven, mongo java driver and others.

Whole Maven project was provided by course, with his pom.xml file, packages, classes and others; here is shown the main file Week1Homework3.java:

/*
 * Copyright (c) 2008 - 2013 10gen, Inc. <http://10gen.com>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package com.tengen;

import com.mongodb.AggregationOutput;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;

import java.net.UnknownHostException;

public class Week1Homework3 {
    public static void main(String[] args) throws UnknownHostException {
        MongoClient client = new MongoClient();

        DB database = client.getDB("m101");
        DBCollection collection = database.getCollection("funnynumbers");

        // Not necessary yet to understand this.  It's just to prove that you
        // are able to run a command on a mongod server
        AggregationOutput output =
                collection.aggregate(
                        new BasicDBObject("$group",
                                new BasicDBObject("_id", "$value")
                                        .append("count", new BasicDBObject("$sum", 1)))
                        ,
                        new BasicDBObject("$match", new BasicDBObject("count",
                                new BasicDBObject("$gt", 2))),
                        new BasicDBObject("$sort", new BasicDBObject("_id", 1))
                );

        int answer = 0;
        for (DBObject doc : output.results()) {
            answer += (Double) doc.get("_id");
        }

        System.out.println("THE ANSWER IS: " + answer);
    }
}

Here the compilation and execution of the program, and the answer result obtained:

$ l
pom.xml  src/  target/
$ mvn compile exec:java -Dexec.mainClass=com.tengen.Week1Homework3
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'exec'.
[INFO] ------------------------------------------------------------------------
[INFO] Building M101J-week1-homework3
[INFO]    task-segment: [compile, exec:java]
[INFO] ------------------------------------------------------------------------
[INFO] [resources:resources {execution: default-resources}]
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /src/main/resources
[INFO] [compiler:compile {execution: default-compile}]
[INFO] Nothing to compile - all classes are up to date
[INFO] [exec:java {execution: default-cli}]
[WARNING] Warning: killAfter is now deprecated. Do you need it ? Please comment on MEXEC-6.
THE ANSWER IS: 366
[WARNING] thread Thread[MongoCleaner12877540,5,com.tengen.Week1Homework3] was interrupted but is still alive after waiting at least 15000msecs
[WARNING] thread Thread[MongoCleaner12877540,5,com.tengen.Week1Homework3] will linger despite being asked to die via interruption
[WARNING] NOTE: 1 thread(s) did not finish despite being asked to  via interruption. This is not a problem with exec:java, it is a problem with the running code. Although not serious, it should be remedied.
[WARNING] Couldn't destroy threadgroup org.codehaus.mojo.exec.ExecJavaMojo$IsolatedThreadGroup[name=com.tengen.Week1Homework3,maxpri=10]
java.lang.IllegalThreadStateException
    at java.lang.ThreadGroup.destroy(ThreadGroup.java:775)
    at org.codehaus.mojo.exec.ExecJavaMojo.execute(ExecJavaMojo.java:328)
    at org.apache.maven.plugin.DefaultPluginManager.executeMojo(DefaultPluginManager.java:490)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoals(DefaultLifecycleExecutor.java:694)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeStandaloneGoal(DefaultLifecycleExecutor.java:569)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoal(DefaultLifecycleExecutor.java:539)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeGoalAndHandleFailures(DefaultLifecycleExecutor.java:387)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeTaskSegments(DefaultLifecycleExecutor.java:348)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:180)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:328)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:138)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:362)
    at org.apache.maven.cli.compat.CompatibleMain.main(CompatibleMain.java:60)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
    at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
    at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
    at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 24 seconds
[INFO] Finished at: Wed May 07 11:27:35 COT 2014
[INFO] Final Memory: 17M/41M
[INFO] ------------------------------------------------------------------------
$

HOMEWORK 1.4

ANSWER HOMEWORK 1.4:

Like HW’s 1.1 and 1.3, it was about verifying the correctness of MongoDB installation, example data import, JDK, Maven, mongo java driver, furthermore Spark, Freemarker and others.

Whole Maven project was provided by course, with his pom.xml file, packages, classes and others; here is shown the main file Week1Homework4.java:

/*
 * Copyright (c) 2008 - 2013 10gen, Inc. <http://10gen.com>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package com.tengen;

import com.mongodb.AggregationOutput;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;
import com.mongodb.ServerAddress;
import freemarker.template.Configuration;
import freemarker.template.Template;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import spark.Request;
import spark.Response;
import spark.Route;
import spark.Spark;

import java.io.StringWriter;
import java.net.UnknownHostException;
import java.util.HashMap;
import java.util.Map;

public class Week1Homework4 {
    private static final Logger logger = LoggerFactory.getLogger("logger");

    public static void main(String[] args) throws UnknownHostException {
        final Configuration configuration = new Configuration();
        configuration.setClassForTemplateLoading(
                Week1Homework4.class, "/");

        MongoClient client = new MongoClient(new ServerAddress("localhost", 27017));

        DB database = client.getDB("m101");
        final DBCollection collection = database.getCollection("funnynumbers");

        Spark.get(new Route("/") {
            @Override
            public Object handle(final Request request,
                                 final Response response) {
                StringWriter writer = new StringWriter();
                try {
                    Template helloTemplate = configuration.getTemplate("answer.ftl");

                    // Not necessary yet to understand this.  It's just to prove that you
                    // are able to run a command on a mongod server
                    AggregationOutput output =
                            collection.aggregate(
                                    new BasicDBObject("$group",
                                            new BasicDBObject("_id", "$value")
                                                    .append("count", new BasicDBObject("$sum", 1)))
                                    ,
                                    new BasicDBObject("$match", new BasicDBObject("count",
                                            new BasicDBObject("$lte", 2))),
                                    new BasicDBObject("$sort", new BasicDBObject("_id", 1))
                            );

                    int answer = 0;
                    for (DBObject doc : output.results()) {
                        answer += (Double) doc.get("_id");
                    }

                    Map<String, String> answerMap = new HashMap<String, String>();
                    answerMap.put("answer", Integer.toString(answer));

                    helloTemplate.process(answerMap, writer);
                } catch (Exception e) {
                    logger.error("Failed", e);
                    halt(500);
                }
                return writer;
            }
        });
    }
}

Here the compilation and execution of the program launching the Spark web application:

$ l
pom.xml  src/  target/
$ mvn compile exec:java -Dexec.mainClass=com.tengen.Week1Homework4
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'exec'.
[INFO] ------------------------------------------------------------------------
[INFO] Building M101J
[INFO]    task-segment: [compile, exec:java]
[INFO] ------------------------------------------------------------------------
[INFO] [resources:resources {execution: default-resources}]
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 1 resource
[INFO] snapshot spark:spark:0.9.9.4-SNAPSHOT: checking for updates from Spark repository
Downloading: http://www.sparkjava.com/nexus/content/repositories/spark//org/slf4j/slf4j-simple/1.6.4/slf4j-simple-1.6.4.pom
[INFO] Unable to find resource 'org.slf4j:slf4j-simple:pom:1.6.4' in repository Spark repository (http://www.sparkjava.com/nexus/content/repositories/spark/)
Downloading: http://repo1.maven.org/maven2/org/slf4j/slf4j-simple/1.6.4/slf4j-simple-1.6.4.pom
1K downloaded  (slf4j-simple-1.6.4.pom)
Downloading: http://www.sparkjava.com/nexus/content/repositories/spark//org/slf4j/slf4j-simple/1.6.4/slf4j-simple-1.6.4.jar
[INFO] Unable to find resource 'org.slf4j:slf4j-simple:jar:1.6.4' in repository Spark repository (http://www.sparkjava.com/nexus/content/repositories/spark/)
Downloading: http://repo1.maven.org/maven2/org/slf4j/slf4j-simple/1.6.4/slf4j-simple-1.6.4.jar
7K downloaded  (slf4j-simple-1.6.4.jar)
[INFO] [compiler:compile {execution: default-compile}]
[INFO] Nothing to compile - all classes are up to date
[INFO] [exec:java {execution: default-cli}]
[WARNING] Warning: killAfter is now deprecated. Do you need it ? Please comment on MEXEC-6.
== Spark has ignited ...
>> Listening on 0.0.0.0:4567
636 [Thread-2] INFO org.eclipse.jetty.util.log - jetty-7.3.0.v20110203
710 [Thread-2] INFO org.eclipse.jetty.util.log - Started SocketConnector@0.0.0.0:4567

Finally, the result obtained browsing to the recently launched Spark web application:

Week 2: CRUD

Following are presented the contents and answers to the HomeWorks belonging to Week 2 (CRUD) for “M101J: MongoDB for Java Developers” course offered by https://university.mongodb.com/ started at 2014-03-17.

HOMEWORK 2.1

ANSWER HOMEWORK 2.1:

HOMEWORK 2.2

ANSWER HOMEWORK 2.2:

HOMEWORK 2.3

ANSWER HOMEWORK 2.3:

Code snippet for public boolean addUser(String username, String password, String email) method:

// validates that username is unique and insert into db
public boolean addUser(String username, String password, String email) {

    String passwordHash = makePasswordHash(password, Integer.toString(random.nextInt()));

    // XXX WORK HERE
    // create an object suitable for insertion into the user collection
    // be sure to add username and hashed password to the document. problem instructions
    // will tell you the schema that the documents must follow.
    BasicDBObject doc = new BasicDBObject("_id", username).append("password", passwordHash);



    if (email != null && !email.equals("")) {
        // XXX WORK HERE
        // if there is an email address specified, add it to the document too.
        doc.append("email", email);
    }

    try {
        // XXX WORK HERE
        // insert the document into the user collection here
        usersCollection.insert(doc);
        return true;
    } catch (MongoException.DuplicateKey e) {
        System.out.println("Username already in use: " + username);
        return false;
    }
}

Code snippet for public DBObject validateLogin(String username, String password) method:

public DBObject validateLogin(String username, String password) {
    DBObject user = null;

    // XXX look in the user collection for a user that has this username
    // assign the result to the user variable.
    user = usersCollection.findOne(new BasicDBObject("_id",username));

    if (user == null) {
        System.out.println("User not in database");
        return null;
    }

    String hashedAndSalted = user.get("password").toString();

    String salt = hashedAndSalted.split(",")[1];

    if (!hashedAndSalted.equals(makePasswordHash(password, salt))) {
        System.out.println("Submitted password is not a match");
        return null;
    }

    return user;
}

Week 3: Schema Design

Following are presented the contents and answers to the HomeWorks belonging to Week 3 (Schema Design) for “M101J: MongoDB for Java Developers” course offered by https://university.mongodb.com/ started at 2014-03-17.

HOMEWORK 3.1

ANSWER HOMEWORK 3.1:

HOMEWORK 3.2

ANSWER HOMEWORK 3.2:

Code snippet for public DBObject findByPermalink(String permalink) method:

// Return a single post corresponding to a permalink
public DBObject findByPermalink(String permalink) {

    DBObject post = null;
    // XXX HW 3.2,  Work Here
    post = postsCollection.findOne(new BasicDBObject("permalink",permalink));



    return post;
}

Code snippet for public List<DBObject> findByDateDescending(int limit) method:

// Return a list of posts in descending order. Limit determines
// how many posts are returned.
public List<DBObject> findByDateDescending(int limit) {

    List<DBObject> posts = new ArrayList<DBObject>();
    // XXX HW 3.2,  Work Here
    // Return a list of DBObjects, each one a post from the posts collection
    DBCursor cursor = postsCollection.find().sort(new BasicDBObject("date",-1)).limit(limit);
    while (cursor.hasNext()) {
        posts.add(cursor.next());
    }

    return posts;
}

Code snippet for public String addPost(String title, String body, List tags, String username) method:

public String addPost(String title, String body, List tags, String username) {

    System.out.println("inserting blog entry " + title + " " + body);

    String permalink = title.replaceAll("\\s", "_"); // whitespace becomes _
    permalink = permalink.replaceAll("\\W", ""); // get rid of non alphanumeric
    permalink = permalink.toLowerCase();


    BasicDBObject post = new BasicDBObject();
    // XXX HW 3.2, Work Here
    // Remember that a valid post has the following keys:
    // author, body, permalink, tags, comments, date
    //
    // A few hints:
    // - Don't forget to create an empty list of comments
    // - for the value of the date key, today's datetime is fine.
    // - tags are already in list form that implements suitable interface.
    // - we created the permalink for you above.

    // Build the post object and insert it
    post.append("author", username).append("title", title).append("body", body).append("permalink", permalink).append("date", new Date()).append("tags", tags).append("comments", new BasicDBList());
    postsCollection.insert(post);


    return permalink;
}

HOMEWORK 3.3

ANSWER HOMEWORK 3.3:

Code snippet for public void addPostComment(final String name, final String email, final String body, final String permalink) method:

// Append a comment to a blog post
public void addPostComment(final String name, final String email, final String body,
                           final String permalink) {

    // XXX HW 3.3, Work Here
    // Hints:
    // - email is optional and may come in NULL. Check for that.
    // - best solution uses an update command to the database and a suitable
    //   operator to append the comment on to any existing list of comments
    BasicDBObject comment = new BasicDBObject("author",name).append("body",body);
    if (email != null && !email.equals("")) {
        // the provided email address
        comment.append("email", email);
    }
    postsCollection.update(
        new BasicDBObject("permalink",permalink),
        new BasicDBObject("$push", new BasicDBObject("comments",comment))
    );


}

Week 4: Performance

Following are presented the contents and answers to the HomeWorks belonging to Week 4 (Performance) for “M101J: MongoDB for Java Developers” course offered by https://university.mongodb.com/ started at 2014-03-17.

HOMEWORK 4.1

ANSWER HOMEWORK 4.1:

HOMEWORK 4.2

ANSWER HOMEWORK 4.2:

HOMEWORK 4.3

ANSWER HOMEWORK 4.3:

HOMEWORK 4.4

ANSWER HOMEWORK 4.4:

Week 5: Aggregation Framework

Following are presented the contents and answers to the HomeWorks belonging to Week 5 (Aggregation Framework) for “M101J: MongoDB for Java Developers” course offered by https://university.mongodb.com/ started at 2014-03-17.

HOMEWORK 5.1

ANSWER HOMEWORK 5.1:

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

HOMEWORK 5.2

ANSWER HOMEWORK 5.2:

use test

db.small_zips.aggregate([
	{"$match":{
		"state":{"$in":["CA","NY"]}
	}},
	{"$group":{
		"_id":{"city":"$city","state":"$state"},
		"pop":{"$sum":"$pop"}
	}},
	{"$match":{
		"pop":{"$gt":25000}
	}},
	{"$group":{
		"_id":null,
		"average_requested":{"$avg":"$pop"}
	}}
])

HOMEWORK 5.3

ANSWER HOMEWORK 5.3:

use test

db.grades.aggregate([
	{"$unwind":"$scores"},
	{"$match":{
		"scores.type":{"$ne":"quiz"}
	}},
	{"$group":{
		"_id":{"student_id":"$student_id", "class_id":"$class_id"},
		"average_student":{"$avg":"$scores.score"}
	}},
	{"$project":{
		"_id":false,
		"student_id":"$_id.student_id",
		"class_id":"$_id.class_id",
		"average_student":true
	}},
	{"$group":{
		"_id":"$class_id",
		"average_class":{"$avg":"$average_student"}
	}},
	{"$sort":{
		"average_class":-1
	}},
	{"$limit":1}
])

HOMEWORK 5.4

ANSWER HOMEWORK 5.4:

use test

db.zips.aggregate([
	{"$match":{
		"city":{"$regex":/^\d+/}
	}},
	{"$group":{
		"_id":null,
		"sum_rural":{"$sum":"$pop"}
	}}
])

Week 6: Application Engineering

Following are presented the contents and answers to the HomeWorks belonging to Week 6 (Application Engineering) for “M101J: MongoDB for Java Developers” course offered by https://university.mongodb.com/ started at 2014-03-17.

HOMEWORK 6.1

ANSWER HOMEWORK 6.1:

HOMEWORK 6.2

ANSWER HOMEWORK 6.2:

HOMEWORK 6.3

ANSWER HOMEWORK 6.3:

HOMEWORK 6.4

ANSWER HOMEWORK 6.4:

HOMEWORK 6.5

ANSWER HOMEWORK 6.5:

Final Exam

Following are presented the contents and answers to the questions belonging to Final Exam for “M101J: MongoDB for Java Developers” course offered by https://university.mongodb.com/ started at 2014-03-17.

Final: Question 1

Final: Question 1. Answer:

$ l
enron.zip
$ unzip enron.zip
Archive:  enron.zip
   creating: dump/enron/
  inflating: dump/enron/messages.bson  
  inflating: dump/enron/messages.metadata.json  
$ l
dump/  enron.zip
$ /opt/mongodb-linux-i686-2.6.0/bin/mongorestore
connected to: 127.0.0.1
2014-05-08T14:20:31.377-0500 dump/enron/messages.bson
2014-05-08T14:20:31.377-0500 	going into namespace [enron.messages]
2014-05-08T14:20:34.690-0500 		Progress: 67557346/396236668	17%	(bytes)
2014-05-08T14:20:37.006-0500 		Progress: 106126234/396236668	26%	(bytes)
2014-05-08T14:20:40.255-0500 		Progress: 139318935/396236668	35%	(bytes)
2014-05-08T14:20:43.108-0500 		Progress: 188432810/396236668	47%	(bytes)
2014-05-08T14:20:46.008-0500 		Progress: 227400576/396236668	57%	(bytes)
2014-05-08T14:20:49.030-0500 		Progress: 282543056/396236668	71%	(bytes)
2014-05-08T14:20:52.128-0500 		Progress: 332774078/396236668	83%	(bytes)
2014-05-08T14:20:55.102-0500 		Progress: 372492093/396236668	94%	(bytes)
120477 objects found
2014-05-08T14:20:57.348-0500 	Creating index: { key: { _id: 1 }, ns: "enron.messages", name: "_id_" }
$ l
dump/  enron.zip
$

> show dbs
admin    (empty)
blog     0.078GB
final7   0.078GB
local    0.078GB
m101     0.078GB
school   0.078GB
test     0.078GB
weather  0.078GB
> show dbs
admin    (empty)
blog     0.078GB
enron    0.953GB
final7   0.078GB
local    0.078GB
m101     0.078GB
school   0.078GB
test     0.078GB
weather  0.078GB
> use enron
switched to db enron
> show tables
messages
system.indexes
> db.messages.count()
120477
>

$ l
dump/  enron.zip  final01_00.js
$ cat final01_00.js
use enron
query = {"headers.From":"andrew.fastow@enron.com", "headers.To":"john.lavorato@enron.com"}
db.messages.find(query).count()
$ /opt/mongodb-linux-i686-2.6.0/bin/mongo < final01_00.js
MongoDB shell version: 2.6.0
connecting to: test
switched to db enron
{
	"headers.From" : "andrew.fastow@enron.com",
	"headers.To" : "john.lavorato@enron.com"
}
1
bye
$ l
dump/  enron.zip  final01_00.js
$ cat final01_00.js
use enron
query = {"headers.From":"andrew.fastow@enron.com", "headers.To":"jeff.skilling@enron.com"}
db.messages.find(query).count()
$ /opt/mongodb-linux-i686-2.6.0/bin/mongo < final01_00.js
MongoDB shell version: 2.6.0
connecting to: test
switched to db enron
{
	"headers.From" : "andrew.fastow@enron.com",
	"headers.To" : "jeff.skilling@enron.com"
}
3
bye
$

Final: Question 2

Final: Question 2. Answer:

use enron
db.messages.aggregate([
	{$unwind:"$headers.To"},
	{$group:{
		_id:{id:"$_id",from:"$headers.From"},
		tos:{$addToSet:"$headers.To"}
	}},
	{$unwind:"$tos"},
	{$group:{
		_id:{
			from:"$_id.from",
			to:"$tos"
		},
		count:{$sum:1}
	}},
	{$sort:{
		count:-1
	}},
	{$limit:5}
])

MongoDB shell version: 2.6.0
connecting to: test
switched to db enron
{ "_id" : { "from" : "susan.mara@enron.com", "to" : "jeff.dasovich@enron.com" }, "count" : 750 }
{ "_id" : { "from" : "soblander@carrfut.com", "to" : "soblander@carrfut.com" }, "count" : 679 }
{ "_id" : { "from" : "susan.mara@enron.com", "to" : "james.steffes@enron.com" }, "count" : 646 }
{ "_id" : { "from" : "susan.mara@enron.com", "to" : "richard.shapiro@enron.com" }, "count" : 616 }
{ "_id" : { "from" : "evelyn.metoyer@enron.com", "to" : "kate.symes@enron.com" }, "count" : 567 }
bye

Final: Question 3

Final: Question 3. Answer:

// use enron
query = {"headers.Message-ID":"<8147308.1075851042335.JavaMail.evans@thyme>"}
change = {$push:{"headers.To":"mrpotatohead@10gen.com"}}
db.messages.update(query,change)
db.messages.findOne(query)

Final: Question 4

Final: Question 4. Answer:

Code snippet for public void likePost(final String permalink, final int ordinal) method:

public void likePost(final String permalink, final int ordinal) {

// XXX Final Exam, Please work here
// Add code to increment the num_likes for the 'ordinal' comment
// that was clicked on.
// provided you use num_likes as your key name, no other changes should be required
// alternatively, you can use whatever you like but will need to make a couple of other
// changes to templates and post retrieval code.
    postsCollection.update(new BasicDBObject("permalink",permalink), new BasicDBObject("$inc", new BasicDBObject("comments."+ordinal+".num_likes",1)));
}

Final: Question 5

Final: Question 5. Answer:

Final: Question 6

Final: Question 6. Answer:

Final: Question 7

Final: Question 7. Answer:

use final7
counter = 1
cursor_images = db.images.find(); null;
while (cursor_images.hasNext()) {
	current_image = cursor_images.next()
	if (! db.albums.find({images:current_image._id}).hasNext()) {
		print('['+counter+++'] Orphan image found in images collection to remove:\n'+JSON.stringify(db.images.findOne(current_image))+'\n')
		db.images.remove(current_image)
	}
}

Final: Question 8

Final: Question 8. Answer:

Final: Question 9

Final: Question 9. Answer:

Final: Question 10

Final: Question 10. Answer:

PROGRESS

CERTIFICATE

REFERENCES

• https://university.mongodb.com/
• http://api.mongodb.org/
• http://www.mongodb.com/
• http://hao-deng.blogspot.com/search/label/Mongodb
• http://ankurthetechie.blogspot.com/2013/09/final-exam-answers-with-explanation-for.html
• http://techinote.com/mongodb-final-exam/