Ronnie Saurenmann Principal Architect Microsoft Switzerland

Objects XML.NET Language Integrated Query C# 3.0VB 9.0Others… Relational LINQ to Objects LINQ to SQL LINQ to XML LINQ to Entities LINQ to DataSets

Application SQL Server LINQ to SQL from c in db.Customers where c.City == "London" select c.CompanyName LINQ Query SQL Query SELECT CompanyName FROM Cust WHERE City = 'London' Rows ObjectsSubmitChanges() DML or SProcs db.Customers.Add(c1); c2.City = "Barcelona"; db.Customers.Remove(c3); INSERT INTO Cust … UPDATE Cust … DELETE FROM Cust …

DataContext Strongly typed database connection Designer Relationships One-to-one, one-to-many Inheritance Custom types Intellisense and compiler validation “Strongly typed query” Super easy to write query

Relationships Pre-defined joins No need to declare the join in the query Ad hoc joins Inner joins and grouped joins Hierarchical navigation

Stored procedures support For Reads For Inserts, Updates and Deletes Custom SQL Queries DataContext1.Execute…. Custom Types Instead of anonymous types (var) Can use the designer or your own class

Change tracking Updates through dynamic SQL DML or stored procedures Ugly: no client side change tracking Optimistic concurrency Using version numbers, time stamps, or previous values Tip: use timestamps when possible Deep save with foreign key order Customers  Orders

Property change notification OnLimitChanging(decimal value) Ugly: watch out deserialization!.SubmitChange notification OnValidate(System.Data.Linq.ChangeAction action) DataContex UpdateCreditCardLimit(CreditCardLimit instance) SubmitChanges(System.Data.Linq.ConflictMod e failureMode)

Optimized with new row_count feature in SQL Server 2005 Page 1 or Page same speed Query stops as soon as it has the right page size (e.g 10 rows) Only the page size (e.g. 10 rows ) is transferred from the DB Falls back to a simpler version on SQL 2000 ASP.NET LinqDataSource Control Automatically done Custom made with “skip()” and “take()”

Change tracking in stateless environment ASP.NET Understand when query are executed and how Lazy vs. Eager Loading

DataContext is in charge for the Change Tracking DataContext is not serializable It cannot be put on Session state (anyway it would be bad) Change tracking should be stateless Manually store in ViewState original values or better timestamp LinqDataSource does it automatically Stores original values in ViewState

Page1 instance DataContex instance DataContex instance Response Submit Browser Request Page1 new instance New DataContex instance New DataContex instance Changes to the “Customer” object done on the 2 nd request Need to send back original and new values Changes to the “Customer” object done on the 2 nd request Need to send back original and new values

Lazy vs. Eager Loading Ugly: Eager loading at DataContext only affects all queries! Understanding when query are executed Query composition In memory query Good: for caching scenario

No disconnected client side change tracking! For the moment need to build your own Real drawback for multi tier architecture

Service instance DataContex instance DataContex instance Response SaveData WPF / WinForm / Silverlight GetData Service new instance New DataContex instance New DataContex instance Response Changes done on the client “Customer” object Need to manually send back original values Changes done on the client “Customer” object Need to manually send back original values

Works only with SQL Server Very hard to write a provider Competition from ADO.NET Entity Framework Will have other providers like Oracle Will not have multi tier change tracking support neither Shipping 2H 2008

The Good Easy to use Very powerful for read operations Absolutely recommended for 2-tier app Good for most ASP.NET architectures Where Data Access Layer and Presentation Layer are in the same process Released

The Bad The Challenging Change tracking in stateless environment (ASP.NET) Understand when query are executed and how Lazy vs. Eager Loading The Ugly Doesn't have multi tier change tracking support ADO.NET Entity Framework is an alternative Works only with SQL Server

Use the SQL Profiler all the time!!

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