DEVELOPING APPLICATIONS WITH LINQ 2 SQL

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DEVELOPING APPLICATIONS WITH LINQ 2 SQL

• Sidar Ok
• http//www.sidarok.com

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• Common Glossary
• Problem
• Building in house ORM/DAL vs Use an existing one
• Linq to SQL Comes into play Myths and Realities
• Linq to SQL beyond drag and drop Concepts

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• Linq to SQL Entity Model
• Mapping Engine
• Attribute Level or External ?
• SQL Metal to rescue
• What it does, what it lacks
• Understanding DataContext
• Change Management Change Communication
  Strategies

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• Debugging and Troubleshooting
• Transaction Handling
• Concurrency Conflict Handling Scenarios
• Entity Validation
• Security Model
• Serialization
• Performance Advices Best practices

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Common Glossary

• ORM (Object Relational Mapper)
• Lazy (Deferred) Loading
• Eager Loading
• Unit of Work Pattern
• Object (Dirty) Tracking
• Repository Pattern
• Law of Leaky Abstractions
• Plain Old CLR Objects (POCO)
• Persistence Ignorance
• TPH Model mapping
• DTO (Data Transfer Objects)

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Problem

• Advanced programming in relational system Pain
  of Hell redefined on earth
• Impedance Mismatch
• Re-Inventing the Flat Tire ? Over and Over ?
• Basic CRUD ?
• Reacting to changes, maintainability

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Solutions

• Putting Everything in DB
• Utilizing Custom Code Generation
• Using an Object Database
• Using a ready to go ORM
• Linq to SQL
• Entity Framework
• Nhibernate (Open Source)
• LLBLgen

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Advises on Building Custom DAL/ORM
Caching
Transactions
Concurrency
Subquerying
DONT
Lazy Loading
Cascading CRUD
Configurability
Aggregation
Dependency Order
Debugging
Identity Management
Multi-Threading
Paging
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Linq to SQL into the pitch

• Microsofts Full Linq provider for MS SQL
• Built on top of ADO.NET
• Previously owned by C, now ADO.NET
• A designer and a RAD environment
• Plays well with System.Transactions
• Supports TPH model
• Supports custom queries stored procedures

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Myths Realities

• L2S is for less advanced users
• L2S is slow
• L2S saves me building DAL
• L2S just supports SQL 2005
• 2000, 2005, 2008 CE
• L2S doesnt have an N-Tier story
• You have to have a db schema first
• You have to have attributes

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Limitations and Drawbacks

• L2S doesnt support
• Other DB vendors (Oracle, MySql etc)
• FYI There is a DBLinq project -http//code2code.ne
  t/DB_Linq/
• Multi table mapping
• Many to Many associations
• Designer experience isnt the best
• Batched queries not supported OOTB
• Work disconnected, track yourself

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Beyond Drag Drop L2S Concepts

• Object Tracking
• Deferred Loading
• Load Options
• Optimistic Concurrency
• Change Conflicts
• Change Sets

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L2S Default Entity Model

• Entity Classes are partial
• Drawback Extension only in same assembly
• Entities implement INotifyPropertyChanging,
  INotifyPropertyChanged interfaces
• (1-1) -gt EntityRefltTgt ,
• (1 - ) -gt EntitySetltTgt
• Bunch of partial Methods (OnLoaded, OnCreated
  etc.)

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Mapping Engine

• System.Data.Linq.Mapping namespace
• Mapping Engines Built in
• Attribute Based (Internal Mapping)
• Xml Based (External Mapping)
• L2S Designer doesnt support XML Based
• But SQL Metal tool does

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Demo
Domain First Development with XML Mapping
POCOs
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Sql Metal Can and Cants

• CAN Generate Entities
• Option of Pluralizing Names
• Option of giving them a base class
• CAN Generate DBML
• CAN Select from VB or C
• CANT Partially Generate
• CANT Use on a Recursive SP
• There are alternatives
• T4 Generation by Damien Guard (www.damieng.com)

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Understanding DataContext

• A DataContext is a Unit of Work (UoW)
• Multiple DataContexts can share connections
• Work Modes
• Connected Disconnected
• .SubmitChanges
• Transactional
• Overload with Conflict Mode
• DataContext is the boss

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DataContext is da boss

• Connected Mode
• Life is easy
• Throw an retrieve everything to/from DC
• Object Tracking is a joy
• Not very likely to happen ?
• Disconnected Mode
• Attach untracked objects for Update Delete
• Object Tracking doesnt work

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Change Tracking Strategies

• Track changes in UI
• UI Box knows what it changed
• Pros
• EntityBase, easy to implement
• Hitting DB only once
• Cons
• UI has to keep track
• Keeping track retrieving status from
  association trees can be daunting
• Sending whole tree back is proven to be chatty

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Sequence Diagram
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Change Tracking Strategies (contd)

• Retrieving Entity Tree from DB
• Hitting the DB to get original version and
  compare
• Pros
• UI doesnt need state management
• DAL doesnt care about any state, no implied
  contracts
• Cons
• Hitting DB twice to retrieve
• Needs a robust concurrency error handling
  scenario
• Still sending whole tree, chatty

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Change Tracking Strategies(contd)

• Designing change DTOs
• Sending only change sets as DTO s
• Pros
• Decreases the communication cost in both ways
• Encourages use of DTO s
• Cons
• Still change tracking on the client boxes
• Not trivial to implement
• Mappings from/to DTO can be drudge

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Change Tracking Strategies(contd)

• Designing change DTOs
• Sending only change sets as DTO s
• Pros
• Decreases the communication cost in both ways
• Encourages use of DTO s
• Cons
• Still change tracking on the client boxes
• Not trivial to implement
• Mappings from/to DTO can be drudge

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Demo
Developing Applications In Disconnected
Mode (aka Multi Tier Fairy Tale)
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Sum up

• Writing a custom ORM usually means reinventing
  the wheel
• Linq to SQL is a relatively powerful ORM
• It is an abstraction over SQL Server
• DataContext is at the center of all, implementing
  UoW pattern
• One can plug own mapping source
• Supports POCOs natively
• Only supports TPH Model

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Advanced Topics

• Debugging and Troubleshooting
• Transaction Handling
• Concurrency Conflict Handling Scenarios
• Entity Validation
• Security Model
• Serialization
• Performance Advices Best practices

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Thanks for listening !

• Questions ?
• http//www.sidarok.com
• http//cork.mtug.ie