C#

LINQ Tutorials

May 14, 2017 by ashish Leave a Comment

In these LINQ Tutorials you will understand what is LINQ and how to use LINQ.

LINQ stands for Language Integrated Query.It is used for writing queries using .NET language such as C#.Data consumed by application comes from different data sources so there is some complexity involved when accessing data from different data sources.When accessing data from XML data source you need to write XML access logic in your application.So you need to mix C# or VB.NET code with XML access logic.We can use the same query syntax to work with different data types such as SQL,Text.

In LINQ we use same query syntax to work with different data sources such as SQL,Text.

Use of LINQ Language Integrated Query enables us to write queries using C# or VB.NET.

LINQ to Objects LINQ flavor used to Query in memory collections.

LINQ Queries Main LINQ Query Operators

references:

https://en.wikipedia.org/wiki/Language_Integrated_Query

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Use of LINQ

May 14, 2017 by ashish Leave a Comment

Use of LINQ

Every application needs to work with data.Whether it is a small application or enterprise application ,all the application needs to store details such as the users,data to display,data related to problem domain.

Most of the languages provides different ways to manage the different types of data.For example in C# you can retrieve and update data from different sources:

Databases such as SQL Server,Oracle
XML files
Text Files
JSON data

.NET provides different technologies for working with these different data sources.For example for working with databases you can write SQL queries and execute them using ADO.NET.For XML data you can using XML APIs such as XPath.Though these different APIs makes working with different data sources convient ,it has one big disadvantage.We need to learn different APIs to work with these different data sources.
This is problem is solved by LINQ.LINQ stands for Lnaguage Integrated Query and allows us to use the same language syntax to query different data sources.

ashish

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LINQ to objects

May 14, 2017 by ashish Leave a Comment

LINQ is of different types based on the source of data.For example for querying in-memory data sources or collections LINQ to objects is used.

LINQ to objects is used for querying collections such as List<T>.Any collection which implements IEnumerable<T> or IEnumerable interfaces can be queried using LINQ.

Arrays can be querid using LINQ queries since it implements IEnumerable.

Below is a sample LINQ to Objects query.

string[] users = { "Marc","John","Robin","Prashant" };
var lstUsers = from user in users
where user="Marc"
select user;

This is called query expression.

We can also write the above query using query operators:

var lstUsers =
users.Where(user => user=="Marc")
.Select(user);

In the above example we have used the following query operators:

Where Where operator is used to filter the collection based on the given condition.In this example we have specified the condition that user should be equal to Marc
Select Select operator is used to project or return values as specified.Here we are returning the user.The return values of the operator is also IEnumerable<T>.

Following are some of the main LINQ query operators:

Use	Query operator
Filtering	Where
Projection	Select
Partitioning	Skip, SkipWhile, Take, TakeWhile
Ordering	OrderBy, OrderByDescending,ThenBy
Grouping	GroupBy
Set	Intersect

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IEnumerable and IQueryable interfaces in C#

May 12, 2017 by ashish Leave a Comment

IEnumerable is an interface which is implemented by collections.It is used to iterate over the collection elements.
Some of the features of this interface are:

It is used to iterate over a collection in forward direction.
It can not be used to modify collection elements.
A collection implementing this interface can use foreach loop to iterate the collection elements.
It is used to execute LINQ queries on in memory collections.
So IEnumberable should be implemented by a collection class when the collection needs to be iterated using foreach loop.Most of the collection classes such as list implements this interface.

IQueryable is an interface which inherits IEnumerable interface.There are some differences between IEnumerable and IQueryable interfaces:

While IEneumberable is implemented by collections which wants to execute queries in memory,IQueryable is implemented by collections which wants to execute remote queries such as on database server.
While IEneumberable is used for LINQ to Objects queries,IQueryable is used for LINQ to SQL queries.
In IQueryable, LINQ queries are executed on the remote server such as database server unlike IEnumberable which executes queries in-memory

ashish

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Calculate age from DateofBirth in C#

May 12, 2017 by ashish Leave a Comment

When working in any application many times we want to get the current age of a person from date of birth.We can easily implement this functionality in C# using the Substract method of DateTime class.

To Calculate age from DateofBirth in C# we need to use the DateTime type and Math class.

In the following example we are using the Round() method of the Math class to convert the years from the total number of days.We are calculating the total number of days using the TotalDays property of TimeSpan data type.

private static void GetAgeFromDateofBirth(int year,int month,int day)
{
var today = DateTime.Today;
// Calculate the age.
DateTime birthdate = new DateTime(1978, 7, 26);
var age = today.Subtract(birthdate).TotalDays;

var years = (age / 365);

Math.Round(years);
}

ashish

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