1. LINQ gives a set of query operators that are available as C# Keywords. Those keywords will be used to denote/define an expression ie. Query Expression that retrieves tha data you want.
2. Source data for a query must implement IEnumerable
3. Datasource of LINQ can be array or an array list that supports non-generic IEnumerable interface.
Example of LINQ to Objects(LINQ Implementation)
LINQ query that retrieves key values from a sorted list
so the query expression to select the names from the list:
var nameList= from names in markList
To execute the query the code is:
foreach (var name in nameList)
strName+= name + "\n";
MessageBox.Show(strName,"Names from the list");
Important C# keywords for LINQ:
from -> Retrieves source of data for a query
where -> Tells which elements are retrieved from the data source
orderby ->For sorting
select -> Return contents
group -> Group by (aggregate on groups).
join -> Connecting data from two data sources
Using LINQ with SQL Server
Step 1: Object model creation that maps to the data model of the database.
Step 2: Query definition
Steo 3: Query Execution
Code to use LINQ to query the EmployeeDetails table in EmployeeList database
EmployeeList db=new EmployeeList();
var employees=from employee in db.EmployeeDetails
where employee.Age >25
Object Model provides a measure as a link between objects used by application and objects in a relational database. Object model can be written in C#.
i. Object Relational Designer can be used to create object model.
ii. Implementation of LINQ to work with relational DB is called as LINQ to SQL.(Till date LINQ to SQL can be used with only SQL Server DB).
iii. LINQ to SQL can insert, update, delete and select data.
Use of Object Relational Designer will be shared in Part-II.