This learning note follows the tutorial MongoDB In 30 Minutes on Youtube.

Set up

• Download and install
• make a few folders where you want to store your database
• and set the path to be used by mongodb:
  • mongod --directoryperdb --path 'directory' --logpath 'logpath/mongo.log' --logappend --rest --install installs the mongodb as a rest service
• Now we can run the service: net start MongoDB(This is for windows only). the MongoDB now can run on the background as a service.
• type in mongo and you are in the mongoDB shell.

Usual commands

• show dbs: shows all the databases, don;t touch the default database local
• use databasename: creates a new database
• db shows you the current database you are in.
• MongoDB use JSON format to interact with data. Can contain: string, number, array, objects, basically any normal data structure.

• to create a user:

    db.createUser({
        user:"username",
        pwd:"password",
        roles:["roles of the user"]
    });
  

• db.createCollection('customers') create a collection(table)
• show collections will show all the collections
• db.customers.insert({one json like entry}), note that ‘customer’

Everytime a new entry is inserted, an id is assigned.

• db.customers.find()
• db.customers.find().pretty()
• db.customers.update({first_name:"John"},{first_name:"John", last_name:"...", }): replace an entry with a new entry, The ID does not change. The first parameter is used as a condition like WHERE.

• How to update only one field(change/add/delete): Use operators : $set, $inc, $unset

  db.customers.update({condition},{$$$set:{gender:”male”}}) db.customers.update({condition},{$$$inc:{age:5}}) db.customers.update({first_name:”Steve”},{$$$unset:{age}})

• db.customers.update({first_name:"NoExistName"},{first_name:"NoExistName", last_name:"K",},{upsert:true}); we can add a new entry if it is not find.
• db.customers.update({condition},{$rename:{"gender":"sex"});: change attribute name
• db.customer.remove({conditions},{justOne:true})remove the matching entries, if justOne is not specified, all matches will be deleted.
• db.customers.find($or:[{condition one},{condition two}]) using logic operator.
• $lt,$gt,$lte,$gte: db.customers.find({age:{$lt:40}}).pretty();
• db.customers.find({"address.city":"Boston"}); : using attribute of attribute(member of dictionary, which is also a member of a dictionary). Note: dontforget the quots in "address.city".
• Last one queried a Dictionary, we can also query an Array. For example, every/some entries have attribute membership=['mem1','mem2'] which is an array containing different kinds of memberships. we can do: db.customers.find({membership:"mem1"});
• Sorting by some attribute: db.customer.find().sort({last_name:1}).pretty(). 1 for ascending, -1 for descending.
• Count documents: db.customers.find({conditions}).count();
• Set limit: db.customers.find({conditions}).limit(4).sort({last_name:1});
• Iterate using forEach: db.customers.find().forEach(function(doc){print(doc.first_name)}); this could call javascript function.