linq to object

8/9/2019 LINQ to Object

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Foyzul KarimLINQ to Object


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Why a businessman needssoftware?

To automate his business (data)


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Where does the data stored?

Database, RAM, XML, File etc


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Working with Database

SqlConnection Query Execution procedure etc


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Working with ADO.NET

DataTable DataSet SqlDataAdapter etc


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Working with RAM data

Create user defined class Load its properties with data Arrays etc


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Whats the point?

Different working procedure with differentsyntax


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Find out the differences

var query = fromstudentObject in students

select studentObject;

var query = fromstudentObject in db.students



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Find out the differences

var query = fromstudentObject in students


var query = fromstudentObject in db.students


The left query is used to select data from a list of studentsand the right query is used to retrieve data from studenttable of a database. But the syntax is almost same.

Amazing. Isn't it?


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LINQ

Language Integrated Query


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How it works?

In simplified english:from variable in source

In syntax:

from customerObject in Customers


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How it works?


where the condition is true

In syntax:

from customerObject in Customerswhere customerObject.Name == "Foysal"


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How it works?


where the condition is trueselect data

In syntax:

from customerObject in Customerswhere customerObject.Name == "Foysal"select customerObject;


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Types of LINQ

LINQ to Object LINQ to SQL LINQ to XML


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Types of LINQ

LINQ to Object (Today's agenda) LINQ to SQL LINQ to XML


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LINQ To Object


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Initialization Expression:

Standard object initialization

Student student=new Student();student.Id = "001";

student.Name = "Foysal";student.Address = "Dhaka";

Initialization expression

Student student = new Student{Id = "001", Name = "Foysal",

Address = "Dhaka"};

By using an object initialization expression, we caninitialize an object without calling its constructor and notsetting its properties.


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Anonymous types

By using the anonymous type, we don't have to create aprototype (or we can call it as a class) of our required

data out of many of them.

Example:new {studentObject.Name,studentObject.Address};

The compiler will create a class for our selected values.


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Restriction Operator : Where

This operator allows us to filter our required data from acollection of data.

Example:

var selectedNames = from name in nameswhere name.Length == 6select name;

or

var selectedStudents = from student in studentswhere student.Name.Length == 6

select student;


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Practice:1. Get the student list who live in Shamoli.2. Get the names which has the length of more than 6


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How to work well in .NET

To work better with a tool, you must know what can youdo with that tool. Remember, Language (C# forexample) is just a tool for your coding. So, you have to

know what can you do with this tool.

Linq provides a lot of methods to work on. I am givinganother example of restriction operator in the upcomingslide.


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Example:var selectedNames = from name in names

where name.EndsWith("l")select name;

or

var selectedStudents = from student in studentswhere student.Name.StartsWith("S")

select student;

Restriction Operator : Where


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Practice:1. Find the names which contains the string sequence

of "on"

2. Find the student list who has address containing thestring sequence of "li"


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Projection Operator: Select

By this operator, we select our data in different ways.Example:var selectedNames = from name in names

where name.Contains("Foysal")

select name;

Or,

var selectedStudents = from student in students

where student.Department=="CSE"select student.Name;


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Example:var selectedStudents = from student in students

from course in student.CourseTakenwhere course.CourseName.StartsWith("C")

select student;Or,var selectedStudents = from student in students

from course in student.CourseTakenwhere course.CourseName.StartsWith("C")

select new {student.Name, course.CourseName};

Projection Operator: Select (Cont.)


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Practice:1. Find the courses which are taken by the students who livesin Shamoli.2. Find the course Credit of the courses which are taken by the

students whose name are 6 character long.


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What else we can do with it?There are several more operator in LINQ. Such as:

Partitioning Operators Ordering Operators Grouping Operators Set Operators Conversion Operators

Element Operators Generation Operators Quantifiers Aggregate Operators

Miscellaneous Operators Custom Sequence Operators Query Execution Join Operators Utility Routines


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Next Day: LINQ to SQL

linq to object

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