This is a post on some of the basics of using MongoDB (on Windows).

mongod.exe

So to run the mongo server we use mongod.exe, if all goes well the server will start up and state it’s waiting for connections.

mongo.exe

The JavaScript shell used as the client admin application for the mongo server is named mongo.exe.

Shell Commands

1. use <database> is used to switch the shell to using the named <database>. If this command is not used, be default the test database will be used.
2. show dbs can be used to get a list of all the databases stored in the instance of MongoDB.
3. show collections lists the available collections within the selected database. This is analogous to listing the tables in an SQL database.
4. show users lists the users added to the database. To add a user via the JavaScript Shell we can use the following

   db.addUser({user: "UserName", pwd: "Password", roles: ["readWrite", "dbAdmin"]})
   

   Beware, as the roles are not validated against any schema or role list, so you can assign roles names which are not recognised as specific mongo roles, i.e. I made a typo for dbAdmin and it’s accepted as a role.

5. db is the database object, so we can execute commands such as db.stats()
6. db.myobjects let’s assume we created a database and added some objects into a collection named myobjects. Because we’re using a JavaScript shell we can access the myobjects collection off of the db object. So for example we can now using db.myobjects.count() to get a count of the number of “rows” in the collection. Equally we can use commands such as db.myobjects.find() to list the rows in the collection.

Example workflow

This is a simple example of using mongo.exe to create a database and some data, then querying the database.

For this example we’ll create a CD database which will be used to contain information on all the CD’s we own.

1. If it’s not already running, run mongod.exe
2. In a separate command prompt, run mongo.exe
3. We’ll create the database by typing use CDDatabase, remember it will not be fully created until some data is added to it
5. We can check which database we’re currently viewing by typing db. This will show us we’re in the CDDatabase, but if you now type show dbs you’ll notice the database still doesn’t actually exist in the list of available databases
6. We can now create our first entry in the database. Notice, unlike an SQL database we do not create tables etc. So to create an entry we can type the following

   a = {artist:"Alice Cooper", title:"Billion Dollar Babies", category:"Rock"}
   db.cds.insert(a)
   

   Note: we don’t need to create a variable as we’ve done here, we can just replace ‘a’ in the insert method with the right hand side of the = operator as per

   db.cds.insert({artist:"Alice Cooper", title:"Billion Dollar Babies", category:"Rock"})
   

   So we should have now successfully added an entry into the “cds” collection. Notice again we do not need to define the “cds” collection first, it’s dynamically created when we start using it.

   We can use the command show collections to display a list of the collections that make up the datavase.

   Feel free to add more data if you wish.

7. Let’s now see what’s in the collection dbs. To do this simply type db.cds.find(). You should now see all the entries within the “cds” collection that you created. Notice that a variable _id of type ObjectId has been added to our data.

   To find a single entry, in this example we’ll find the artist by name we simply use db.cds.find({artist:”Alice Cooper”})

8. So as part of the standard CRUD operations on data, we’ve seen how to Create and Read data, now let’s look at updating data. Run the following command

   db.cds.insert({artist:"Iron Maiden", title:"Blood Brothers"})
   

   Now I’m left off the category here, so we now need to update this entry. We use the collection’s update method, thus

   db.cds.update({artist:"Iron Maiden"}, {$set:{category:"Heavy Metal"}})
   

   The first argument in the update method {artist:”Iron Maiden”} is the query string, in other words update where artist is “Iron Maiden”. The second argument is the update action, which simply tells update to set the category to “Heavy Metal”.

   If we run this command we’ll see the category added, but this command works only on the first item found, so if there were multiple “Iron Maiden” entries missing the category this would be a bit of a problem. However we can apply a third argument to update to solve this.

   db.cds.update({category:"Rock"}, {$set:{category:"Heavy Rock"}},{multi:true})
   

   The addition of {multi:true} will allow the update to be applied to all matching entries.

9. Now to the final CRUD operation – Delete. This is simply a case of using the collection’s remove method. For example

   db.cds.remove({artist:"Alice Cooper"})
   

   Be careful not to forget the query part of this method call, the {artist:”Alice Cooper”} as using db.cds.remove() will remove all entries from the collection.