Transcript Slide 1

POC Architecture
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Agenda
LINQ TO SQL
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Architecture
Objects in LINQ-TO-SQL
Examples
Transactions
POC Demo
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LINQ -TO - SQL
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What is LINQ-TO-SQL?
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Provides a runtime infrastructure for managing relational data as objects
without losing the ability to query.
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Application is free to manipulate the objects while LINQ to SQL stays in
the background tracking your changes automatically
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Objects linked to relational data can be defined just like normal objects,
only decorated with attributes to identify how properties correspond to
columns.
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Together, the LINQ to SQL run-time infrastructure and design-time tools
significantly reduce the workload for the database application developer.
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LINQ Architecture
Visual C#
Visual Basic
Others
.Net Language Integrated Query (LINQ)
LINQ-enabled data sources
LINQ-enabled ADO.NET
LINQ
To Objects
LINQ
To Datasets
LINQ
To SQL
LINQ
To Entities
LINQ
To XML
<book>
<title/>
<author/>
<price/>
</book>
Databases
Objects
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XML
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LINQ TO SQL Architecture
from d in db.Doctors
where d.City == “Bangalore"
select c.doctorName
Application
Enumerate
Objects
Db.Doctors.Add(d1);
c2.City = “bangalore”;
db.Doctors.Remove(d3);
SubmitChanges()
LINQ to SQL
Rows
SQL query
or stored proc
SELECT doctorName
FROM Doctors
WHERE City = ‘Bangalore'
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SQL Server
6
DML
or SProcs
INSERT INTO Doctors …
UPDATE Doctors …
DELETE FROM Doctors …
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Benefits
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Traditionally, queries against data are expressed as simple strings without
type checking at compile time or IntelliSense support.
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We can write queries against strongly typed collections of objects by
using language keywords and familiar operators.
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LINQ applies the principles of object-oriented programming to relational
data.
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It provides a unified programming model for querying data from different
types of Data sources, XML documents, ADO.NET Datasets, and any
collection of objects that supports Ienumerable
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LINQ-enabled languages can provide full type-safety and compile-time
checking of query expressions, and development tools can provide
full intellisense, debugging
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Fully supports transactions, views, and stored procedures.
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Entity Classes
Apply a custom attribute to the top of the class declaration. LINQ to SQL
defines the Table attribute for this purpose.
Example:
[Table(Name="Customers")]
public class Customer
{
[Column(Storage=“_Cust_Id" ,DbType="Int NOT NULL“
,IsPrimaryKey=true)]
public string CustomerID;
[Column(Storage="_City" ,DbType=“VarChar(50) NOT NULL")]
public string City;
}
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Data Context
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A channel or platform by which you retrieve objects from the database
and resubmit changes
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It is initialized with a connection or connection string
Purpose of the DataContext is to translate your requests for objects into
SQL queries made against the database and then assemble objects out of
the results.
public partial class Northwind : DataContext
{
public Table <Customer> Customers;
public Table<Order> Orders;
public Northwind(string connection): base(connection) {}
}
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Data Context Examples
// DataContext takes a connection string
DataContext db = new DataContext("c:\\northwind\\northwnd.mdf");
// Get a typed table to run queries
Table<Customer> Customers = db.GetTable<Customer>();
// Query for customers from London
var q = from c in Customers where c.City == "London"
select c;
foreach (var cust in q)
Console.WriteLine("id = {0}, City = {1}", cust.CustomerID, cust.City);
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Relationships
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LINQ to SQL defines an Association attribute you can apply to a
member used to represent a relationship.
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An association relationship is one like a foreign-key to primary-key
relationship that is made by matching column values between tables.
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Relationships(Master Table)
[Table(Name="City")]
public class City
{
[Column(Id=true)]
public int city_ID;
...
private EntitySet<Doctor> _Doctors;
[Association(Storage="_Doctors", OtherKey="city_id")]
public EntitySet<Doctor> Doctors {
get { return this.Doctors; }
set { this.Doctors.Assign(value); }
}
}
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Relationships (Child Table)
[Table(Name="Doctors")]
public class Doctor {
[Column(Id=true)]
public int doctorID;
[Column]
public string city_ID;
private EntityRef<City> _city;
[Association(Storage="_city", ThisKey="cityID")]
public Customer Customer {
get { return this._city.Entity; }
set { this._city.Entity = value; }
}
}
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LINQ Query Examples
public class Doctor { … }
public class DBHelperDataContext: DataContext
{
public Table<Doctor> Doctors;
…
}
Classes describe
data
Tables are like
collections
Strongly typed
connections
DBHelperDataContext db = new
DBHelperDataContext(…);
var contacts =
from d in db.Doctors
where d.City == “London"
select new { d.doctorName };
Integrated query
syntax
Strongly typed
results
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Query Examples
Ex 1:
var q = from c in db.city
from d in c.Doctors
where c.City == “Bangalore"
select new { c, d };
Ex 2:
var q = from d in db.Doctors
where d.city.cityName == "London"
select new { c = d.Doctors, d };
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Query Examples
Ex: 4
var q = from d in db.Doctors
where d.City == “London"
select d;
foreach (Doctor d in q)
Console.WriteLine(d.doctorName);
The actual type of q in this instance is IQueryable<Customer>.
It's not until the application attempts to enumerate the contents of the
query that it actually executes. In this example the foreach statement
causes the execution to occur.
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Query Examples
var q = from d in db.Doctors
Where d.city == ‘Bangalore’
Select d;
foreach (Doctor d in q)
{
if (d.Speciality ==‘ENT’)
getAppointment(d.Doctor);
}
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Deferred Execution
Actual SQL query is executed when foreach statement is executed
\\Each foreach causes the SQL to be
\\executed
var q = from d in db.Doctors
Where d.City == “London"
select d;
var q = from d in db.Doctors
Where d.City == “London"
select d;
// Execute once using ToList() or
//ToArray()
var list = q.ToList();
foreach (Doctor d in q)
Console.WriteLine(d.doctorName);
foreach (Doctor d in list)
Console.WriteLine(d.doctorName);
foreach (Doctor d in q)
Console.WriteLine(d.CompanyName);
foreach (Doctor d in list)
Console.WriteLine(d.CompanyName);
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Deferred Execution Benefits
var q = from d in db.Doctors
where d.City == "London"
select d;
if (orderByLocation) {
q = from d in q
orderby d.Country, d.City
select d; }
else if (orderByName) {
q = from d in q
orderby d.DoctorName
select d; }
foreach (Doctor d in q) Console.WriteLine(d.DoctorName);
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Object Identity
DataContext manages object identity.
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Whenever a new row is retrieved from the database, it is logged in an
identity table by its primary key and a new object is created.
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Whenever that same row is retrieved again, the original object instance is
handed back to the application.
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In this way, the DataContext translates the databases concept of identity
(keys) into the languages concept (instances).
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In the case that the database contains a table without a primary key,
LINQ to SQL allows queries to be submitted over the table, but it doesn't
allow updates.
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DML Operations
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Inserting
 InsertOnSubmit(entity)
 InsertAllOnSubmit(entityCollection)
 Constraints are not checked early, queries are always sent to the
database.
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Updating
 SubmitChanges()
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Deleting
 DeleteOnSubmit(entity)
 DeleteAllOnSubmit(entityCollection)
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Updating Data
After SubmitChanges() is called
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Modified objects in the object graph are identified.
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New objects to be inserted
Retrieved objects to be deleted
Retrieved objects whose persistent members have changed
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Changes are ordered based on foreign key constraints.
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Database connection is opened and a transaction is started.
Insert, update and delete statements are constructed with modified current values in the set clause and
original values in the where clause for optimistic concurrency conflict detection
If there are any errors, the transaction is rolled back.
If the transaction succeeds, the internal state of the DataContext is changed accordingly.
Database-generated columns like autoincrement / GUID keys and timestamps are propagated back to the
objects
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Exception Handling
DBHelperdataContext db = new DBHelperdataContext();
// make changes here
try
{
db.SubmitChanges();
}
catch (Exception e)
{
// make some adjustments ... // try again
db.SubmitChanges();
}
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LINQ Query to SQL Translation
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LINQ to SQL translates the queries you wrote into equivalent SQL queries and sends them to the server
for processing.
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Because execution is deferred, LINQ to SQL is able to examine your entire query even if assembled from
multiple parts.
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Queries are not transmitted to the server as IL They are in fact transmitted as parameterized SQL queries
in text form.
Example:
var q = from c in db.Contact
where c.DateOfBirth.AddYears(35) > DateTime.Now
orderby c.DateOfBirth descending select c;
Translates to
SELECT [t0].[ContactId], [t0].[FirstName], [t0].[LastName],[t0].[DateOfBirth],[t0].[Phone]
FROM [Contact] AS [t0]
WHERE DATEADD(YEAR, @p0, [t0].[DateOfBirth]) > @p1
ORDER BY [t0].[DateOfBirth] DESC
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Transactions
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A transaction is a service provided by databases or any other resource manager that can be used to
guarantee that a series of individual actions occur automatically; meaning either they all succeed or they
all don't.
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If no transaction is already in scope, the DataContext will automatically start a database transaction to
guard updates when you call SubmitChanges().
Product prod = q.Single(p => p.ProductId == 15);
if (prod.UnitsInStock > 0)
prod.UnitsInStock--;
db.Transaction = db.Connection.BeginTransaction();
try {
db.SubmitChanges();
db.Transaction.Commit();
} catch {
db.Transaction.Rollback(); throw;
}
finally { db.Transaction = null; }
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Demo

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Exception Handling
Application Block
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What is Exception Handling Application Block?
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It is a part of Patterns & Practices Enterprise Library. Patterns &
Practices Enterprise Library is a collection of Application Blocks.
Application Blocks are provided in the form of source code as a guidance
which can be used as it is, can be extended or can be modified as
per the requirements.
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It allows developers and policy makers to create a consistent strategy
for handling exceptions in the application.
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What It Offers?
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It allows administrators and policy makers to create policies to handle
exceptions. They can maintain and modify policies without
changing application code.
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It supports exception handling in all layers of an application
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It allows developers to create their own exceptions.
It provides common tasks which are required at the time of exception
handling. Like logging exception information, replacing original
exception with another exception and wrapping original exception inside
another exception.
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Enterprise Library Installation Information
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Latest version : Enterprise Library 3.1 – May 2007
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System Requirements :
Download Size : 22.9 MB
Link to download :
http://www.microsoft.com/downloads/details.aspx?FamilyId=4C557C63708F-4280-8F0C-637481C31718&displaylang=en
 Operating Systems: Windows Server 2003, Windows Vista, Windows
XP
 Microsoft Framework 2.0 or 3.0
 Microsoft Visual Studio 2005
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Hierarchy of Objects
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Configuration
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Policies
 Exception Types
 Exception Handlers
 Logging Handler
 Wrap Handler
 Replace Handler
 Custom Handler
 Fault Contract Exception Handler
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Configuration
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It is a configuration file of the application which is created to define
policies for exception handling by policy makers. This can be maintained
with the help of Enterprise Library Configuration tool. One can also
modify the configuration file manually.
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Policy
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Policy is a collection of one or more exception types with a given
name. In your policy you include one or more type of exceptions to
handle.
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Only specified exceptions can be handled by the policy and not
others. But if you pass the inherited exception types then they are
handled. If you pass other exception types to the policy then they will not
be handled and same exception will be returned.
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Exception Types
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
It is a list of Exception Types to be handled by a policy.
You can specify Post Handling Action for each exception. Possible
values are:
 None: You don’t want to take any action when this type of exception
occurs. Normally you can take this action with Logging Handler. You
log the exception and do nothing.
 NotifyRethrow: You want to throw the same exception back to the
application. Normally you can take this action with Logging Handler.
You log the exception and throw back the same exception.
Calling method/component can take further action on the exception.
 ThrowNewException:
You want to throw a new exception to the
application. Normally you can take this action with Wrap or Replace
Handler. You wrap or replace original exception and throw a
new exception.
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Exception Handlers
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Logging Handler:
 Logging exception information is a frequently required task as a part
of exception handling.
 With the help of this handler we can log the exception information in
locations specified in the configuration file.
 To use Logging Handler, Logging Application Block must be included
in the application.
 Logging Handler passes the information to the Logging Application
Block to log the exception information.
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Exception Handlers
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Replace Handler:
 You may want to replace the original exception, which
contains sensitive or unnecessary information, with
another more appropriate exception. For example original
exception may contain any URL, any database information
etc.
 New specified exception will be thrown in place of the original
exception.
 New exception can have a customized message.
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Exception Handlers
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Wrap Handler:
 You may want to wrap the original exception inside another
exception. Wrapping will throw a new exception of the specified type
and sets the original exception as InnerException.
 Use wrapping in situations where the calling method/component
can take decisions on the basis of new exception type. And if
required it can use the underlying original exception as well.
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Exception Handlers

Custom Handler:
 You may want to throw your own customized exception type
in place of original exception. For that create an exception
class which implements IExceptionHandler and use it in
the Custom Handler.
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How It Works
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Add the reference of necessary Exception Handling Application Block
DLLs from Enterprise Library into the application. If you are using
Logging Handlers then also take the reference of necessary Logging
Application Block DLLs.
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Create a config file & Define policies into the config file
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How It Works
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How It Works

Deploy the configuration file at all layers of the application where you
want to have Exception Handling functionality.
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Call the policy to handle the exception where you want to use the policy.
You call the policy into the Catch block and pass the exception to the
policy. Policy will execute all handlers one by one assigned for the passed
the exception.
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How It Works
Imports Microsoft.Practices.EnterpriseLibrary.ExceptionHandling
Public Class clsDAL
Public Function GetData() As DataSet
Dim DS As New DataSet
Try
' Data access code will come here.
Catch ex As Exception
Call HandleExceptions(ex)
End Try
Return DS
End Function
Private Sub HandleExceptions(ByVal Ex As Exception)
Dim showErr As Boolean
Dim HandlerEx As New Exception
showErr = ExceptionPolicy.HandleException(Ex, "DALPolicy",
HandlerEx)
If Not HandlerEx Is Nothing Then
Throw HandlerEx
Else
If showErr = True Then
Throw Ex
End If
End If
End Sub
End Class
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Multi-tier architecture View
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Multi-tier architecture View

Exceptions that occur in the data access layer are logged and then
wrapped inside another exception that provides more meaningful
information to the calling layer. Within the business component layer, the
exceptions are logged before they are propagated.

Any exceptions that occur in the business component layer and that
contain sensitive information are replaced with exceptions that no longer
contain this information. These are sent to the user interface (UI) layer
and displayed to the user.
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Thank you