Monday, September 7, 2015

Installing and Using Ruby Interactive Shell on Windows

      Ruby is dynamic,interpreted, object oriented programming languages which is one of the easiest programming language to learn and with Rails its just might be the best web development option at the moment. Ruby intsallation is pretty much simple in windows, Linux and you don't have to install Ruby on Mac. It already has Ruby installed in it.

   Step by step guide to install Ruby on your PC:
  1. Go to Ruby programming language homepage:
  2. Click downloads
  3. Click on Installation-->click on RubyInstaller(Windows)-->Ruby installer-->Download
  4. Select the top selection there that will be the current version of Ruby 
  5. Click save file. let it download
  6. Now double click the file-->accept license agreement-->Install-->finish.

Using Ruby Interactive Shell 

        The interactive shell  or just a shell allows us to type Ruby statements or expressions at the command line and gives immediate result. So open the command prompt and navigate to the folder where Ruby is installed and type "irb".

On ruby shell single number evaluates itself. We can perform simple arithmetic operations the ways show above screenshot. Strings also evaluate to them self, We can perform concatenation operation between two strings using '+' operator as shown below :

         We can also store data in variables and use it later as shown in below "greet' is variable which stores value "good morning". After typing good morning it returns "good morning".

   We can also concatenation "greet" with other value 

    We can write more complicated expressions in ruby shell. We can create functions for example square function in bellow example. Here I wrote my own user define "sqr" function to find square of a number.
     If you have good understanding of function you not even have to write return statement. lets consider following function for addition of two numbers. In which I wrote add method for addition of two numbers when next time I write add(2,2)  it performs addition of these two numbers which is 2+2=4.

Tuesday, March 31, 2015

MongoDB find() and findOne() methods

     In  MongoDB CRUD operation find() and findOne() methods are used to read a documents from the collections. Lets study this methods with example. 

1. find() : 
                  The most basic operation to query documents out of the database is called find(). MongoDB find() method returns all documents present in the database.
 For example, Here I have student database and collection name is grades which has 800 documents. After executing this query it returns first 10 documents and it ask for next 10 documents. If you want more documents type "it" next 10 documents will get display.

    find() method can take some arguments. You can filter result by adding search criteria. For example in "grades" collection there are "homework","quiz" and "exam " type of documents. If I want only "exam" type . The query will be db.grades.find({''type'' :''exam''}).

       We can also add multiple fields in criteria but both the criteria should match. Like here I have selected students with type :exam and you can also include and exclude fields if you want by making field name true or false, here I excluded object id field.

  2. findOne():

 This method also retrieves the data but it returns only one document at a time. Lets see following example fineOne() without argument returns very first document from the collection.

  We can also add criteria in findOne() method like find() method. In following example only document with the "student_id" : 112 is return as specified in criteria.


Saturday, September 20, 2014

MongoDB CRUD Operations

       MongoDB CRUD stands for Create, Read, Update, Delete. MongoDB provides rich semantic to communicate with the database. MongoDB CRUD operations are much similar to SQL create,select,update and delete operations. If you already work with SQL you will find it very easy to understand and if your not then still you will find it very easy! OK, before moving forward to CRUD operation we have to understand how MongoDB stores data. As we know MongoDB is document oriented database it stores the data in the form of documents.
      So no rows and columns. It uses JSON(JavaScript Object Notation) like format to store data. Formally, MongoDB documents are BSON documents. BSON is a binary representation of JSON with additional type information. following image is example of MongoDB document.

     Above document shows fields and values which is much similar to the relational database table but MongoBD uses dynamic schema means you not need to specify datatype, fields before entering data into database such as relational database management system. Following image is example of tabular database.
 In MongoDB there are collections instead of table. In MongoDB database contains number of collections MongoDB stores all the documents in collection. Collection is a group of related documents that have a set of shared common indexes.

Now lets see MongoDB CRUD operations, Mainly include MongoDB read operation and Write operation. It contains some important points such as Cursor, query optimization and distributed queries but we will perform simple operations first for better understanding.
    We will perform the tasks in following order :
  1. Create 
  2. Insert 
  3. Read 
  4. Update 
  5. remove
       Before start performing this operations we have to setup environment means making connection between "mongod" server and "mongo" client. If you don't know how to startup mongo shell then read my previous blog "Downloading and installing MongoDB on windows" 

1. Create:
   lets start from creating database in MongoDB. Now what you have to do is just enter following command on mongo shell,
          use databasename
        use blogdata 
   Database is not created unless you not inserting documents in it.

2. Insert:
     To write into database following syntax is used,
             db.collectionname.insert({ document to be inserted});

      You can use any other folder name instead of "db" if you want.You don't have to create collection separately. It will automatically get created.

        To see the document that you have inserted run this command "db.collectionname.find()", "collectionname" should be the same which you have used earlier to insert document.

  3. Read:
           To read data from the database following command is used,
    By using this command documents will get displayed, you can be more specific by writing some criteria in find(), by default it will display all documents that contains in collection. But if you want to get specific document then Mongo provides way to write more optimized query you can use :

  • Limit the cursor means you can limit the number of result you get which matches criteria.
  • Can add projections means you can specify which fields you want in result.
  • Can add query criteria 

     This query returns documents in which age is greater than 18. It will display only name and address field because it is specified as "1" if field is "0" then mongo does not display that fields in result. Look at following SQL query which gives same result as mongo query for more better understanding.

    4. Update: 
           Update operation is used to modify the documents,
                  db.collectionname.update({ criteria})
            Following query will update the document field "status" as "A" where field "age" has value greater than "18".

     Following SQL query gives the same result as mongo.

   5. Remove: 
        Remove operation is used  to delete documents from database,
         Following query will remove the documents where "status" field is "D".

   See the SQL query for same operation,