基于 MongoDB 的 Web APP（建于 Heroku）－PART 1

最前言

这是我上学期写的文章，算是教程，最初发在我自己的网站上，其实更应该算作是学习笔记吧，因为有些代码我也得回来看一眼才能想起来。从最基础的 MongoDB 的 Shell 端开始学习，然后学习 Web 开发，然后做了个非常简单的 Demo, 基于 MongoDB, Java, Heroku, Spark 和 AngularJS 的 Web App。因为都是用英文学的，学校里与人交流也是用英文，所以就用英文写了，但我最近写的 Swift 学习的几片文章全是中文的，我知道你们都不爱看英文 :) 但这两篇实在是懒得再翻译成中文了。。。所以对 MongoDB 有兴趣的童鞋就将就看看吧。

Foreword

Sometimes you spend tons and tons of time just looking for one method or function or even one simple syntax, but with no result.

Suddenly, you get the answer, and it is on a very common webpage.

"WTF, this is a fking waste of time! Why can't I find it earlier, instead of suffering so much pain?!"

I don't know. Maybe this is exactly the difficulty that stops most people becoming a good engineer. You know, I am still struggling on this way. However, when I write the post, I am happy.

Now, let's get started with our project.)

Add a MongoDB to your Heroku application

First, we need to add a MongoDB database to your Heroku application. There are two choices, Compose MongoDB and mLab MongoDB. Compose MongoDB has no free plan, whereas mLab has a free plan - sandbox. Here I use Compose MongoDB.

To add a Compose database to your Heroku application (using your console):

$ heroku addons:create mongohq:ssd_1g_elastic 

To add a mLab MongoDB (free plan):

$ heroku addons:create mongolab

Use the heroku config command to view your app’s config variables. The URL contains all the MongoDB connection information you will need to connect to your database.

$ heroku config | grep MONGOHQ_URL

Now, you can use the MONGOHQ_URL variable in code and configurations for your driver, depending on the language you app is created in, connecting and authenticating to your MongoDB database hosted with Compose.

Use with Java

==NOTE==: The syntaxes between 2.x and 3.x are very different. If you don't want to waste a lot of time like me, please make it clear what version of mongo-java-driver you are using.

Add the Mongo Java driver to your pom.xml

    org.mongodb
    mongo-java-driver
    3.2.2

And this is apache.maven.plugin:

    org.apache.maven.plugins
    maven-compiler-plugin
    3.5.1
    
        1.8
        1.8
    

Use MongoDB in your application

    MongoURI mongoURI = new MongoURI(System.getenv("MONGOHQ_URL"));
    //get connected
    DB db = mongoURI.connectDB();
    // authenticate
    // (version 2.7.2) db.authenticate(mongoURI.getUsername(), mongoURI.getPassword());
    MongoCredential credential = MongoCredential.createCredential(mongoURI.getUsername(), mongoURI.getDatabase(), mongoURI.getPassword());
    MongoClient mongoClient = new MongoClient(new ServerAddress(), Arrays.asList(credential));

Setting Write Concern

mongoClient.setWriteConcern(WriteConcern.JOURNALED);

As of version 2.10.0, the default write concern is WriteConcern.ACKNOWLEDGED, but it can be easily changed.

Use MongoDB with Spring.

And here is a sample code. (==Note==: this sample is under 2.7.2 version, now the newest is 3.2.2 which I am using)

==Note:== Java MongoDB driver provides its own connection pooling by default, and it's thread safe. See the details in the docs.

CRUD

Get collection names. (like show databases):

Set colls = db.getCollectionNames();
System.out.println("Collections found in DB: " + colls.toString());

Get a collection (for CRUD):

DBCollection coll = db.getCollection("testCollection");

Let's assume a json dataset like this:

{
“name” : “MongoDB”,
“type” : “database”,
“count” : 1,
“info” : {x : 203, y : 102}
}

To insert this dataset into MongoDB, there are two ways shown bellow. I prefer using .append.

BasicDBObject doc = new BasicDBObject("name", "MongoDB")
    .append("type", "database")
    .append("count", 1)
    .append("info", new BasicDBObject("x", 204).append("y", 103));
    coll.insert(doc);

Another way to insert data.

     BasicDBObject doc = new BasicDBObject();
     
     doc.put(“name”, “MongoDB”);
     doc.put(“type”, “database”);
     doc.put(“count”, 1);
     
     BasicDBObject info = new BasicDBObject();
     
     info.put(“x”, 203);
     info.put(“y”, 102);
     
     doc.put(“info”, info);
     
     coll.insert(doc);

Get the first document：

DBObject myDoc = coll.findOne();
System.out.println(myDoc);

Get the total amount of documents：

System.out.println(coll.getCount());

Using a Cursor to Get All the Documents:

DBCursor cursor = coll.find();
try {
while(cursor.hasNext()) {
System.out.println(cursor.next());
}
} finally {
cursor.close();
}

Getting A Single Document with A Query：

BasicDBObject query = new BasicDBObject("name", "MongoDB");

DBCursor cursor = coll.find(query);

try {
    while(cursor.hasNext()) {
        System.out.println(cursor.next());
    }
} finally {
    cursor.close();
}

You may know this kind of statement, which is in shell:

$ db.things.find({j: {$ne: 3}, k: {$gt: 10} });

You can implement in the java driver, using embedded DBObjects:

query = new BasicDBObject("j", new BasicDBObject("$ne", 3))
    .append("k", new BasicDBObject("$gt", 10));

cursor = coll.find(query);

try {
while(cursor.hasNext()) {
    System.out.println(cursor.next());
}
} finally {
cursor.close();
}

Create index list:

//create index，1 for ascending，-1 for descending
coll.createIndex("name"); //Forces creation of an ascending index on a field with the default options.
//get the index list
List list = coll.getIndexInfo();
for (DBObject o : list) {
System.out.println(o);
}

See more methods of DBCollection please refer to this docs. You can also find other index types there.

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