Applied Linq

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(No Transcript)
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Applied Linq
Putting Linq to work
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Introducing

• Class-A
• Kennisprovider Microsoft development
• Training
• Coaching
• http//www.class-a.nl
• Alex Thissen
• Trainer/coach
• http//blog.alexthissen.nl

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Agenda

• About Linq and queries
• Query providers and APIs
• What it means to apply Linq
• Language and code
• Query execution
• Recommendations
• Architecture
• Beyond Linq
• Demos
• Questions and discussion

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Introducing Linq

• Uniform way to write queries over data
• Linq is about query keywords
• Built into new languages C 3.0 and VB 9.0
• Linq is about query operators
• 40 standard query operators are defined
• Methods that operate in queries or act on its
  results

Dim query From c In customers _
Where c.Orders.Count gt 100 _ Order By
c.CompanyName Descending _ Select c
var query from c in customers where
c.Orders.Count gt 100 orderby
c.CompanyName descending select c
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About Linq queries

• Expressed in terms of CLR types
• Objects that might or might not exist in-memory
• Linq queries are not SQL queries at all
• Compositional and hierarchical by nature
• Arbitrary nesting of queries
• Additional operators can be applied to query
• Declarative instead of imperative
• Tell what you want, not how
• How is up to underlying implementation

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Writing queries

• Learn the keywords and operators
• Not all operators have corresponding keywords or
  language integration
• Number of keywords may vary per language
• Some parts must be written with operators
• Usually exposes lambda expressions
• Queries can be done without keywords
• Explicit dot notation (what compiler creates)
• Sometimes FLWOS is overkill

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Query samples
var query from c in customers select
c.Orders.Sum(o gt o.Amount) var query2 (from c
in customers select c.Country).Distinct()
Customer someCustomer customers.FirstOrDefaul
t(c gt c.ID 1337)
Dim query _ From c In customers _ Select
c.Orders.Sum( _ Function (o As Order)
o.Amount) _ ) Dim query2 From c In customers
_ Select c.Country _ Distinct

• VB Lambda expressions will appear in Beta 2

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Demos

• Getting familiar with Linq queries
• Query operations selection, projection, grouping
• Using keywords and operators

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Sources of data

• Your data must come from somewhere
• In-memory CLR objects
• Database
• XML
• Other repositories registry, Active Directory,
• Various flavors of Linq disclose certain type of
  data
• Query syntax does not change per source
• Set of keywords and operators available might be
  different

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Linq to XML

• Power of Linq brought to data in XML format
• Perform queries over XML data
• New element-centric API to manipulate XML
• Faster alternative to System.Xml DOM API
• Functional construction of XML data with query
  expressions

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Linq to SQL

• Generates object model to represent data
• Mapping of CLR types to database tables
• Object/Relational Mapping (OR/M) technology
• 11 relationships between objects and tables
• Translates Linq queries to SQL statements
• Builds on ADO.NET and .NET Transactions
• Persistence services
• Automatic change tracking and identity management
  of objects
• Updates by SQL statements or stored procedures

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Mapping strategy

• Relationships map to collection properties
• Single table inheritance is supported

Data context
Customer object
Order objects
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Two kinds of Linq
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Query providers

• Out-of-the-box providers in .NET 3.5
• Linq to Objects
• Linq to SQL
• Sources in query determine query providers
• Affects keywords and operators you can use
• Query providers can translate Linq queries to
  some implementation
• Most providers come with Linq-enabled APIs
• New object models to work with data
• Linq to Objects has several Linq to XML, DataSets

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Demo

• Linq applied
• Scenario WCF services using untyped Messages

WPF Application
WCF Service
SOAP messages
Linq to XML API
WCF proxy
Linq to XML
Linq to SQL
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New language features C and VB

• Linq keywords
• Extension methods
• Lambda expressions
• Local variable inference
• Object and collection initializers
• Anonymous types
• Automatic properties
• Partial methods

new
new
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Visual Basic 9.0

• Deep XML support
• Express XPath axes with XML properties
• Allows XML literals to appear inside of code

root.ltCustomergt Direct child
elementscustomer._at_CompanyID Attribute
selectiondoc...ltdescriptiongt All descendants
Dim fragment As XElement _ ltcompanygt
ltcitygtHedellt/citygt lt/companygt
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Visual Basic 9.0

• Gives you expression holes inside XML literals
• Additional keywords
• More freedom on order of keywords

Dim query _ From c In doc...ltCustomersgt _
Select ltcustomer IDlt c._at_CustomerID gt gt
lt customer.ltNamegt gt phonelt
customer...ltPhonegt(0) gt lt/customergt
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Demo

• Visual Basic
• WCF sample revisited
• Deep XML support

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Deferred execution

• Most Linq query providers are implemented using
  lazy evaluation
• Composed query expressions do not execute
  immediately
• Queries only execute when necessary
• Performing an iteration over resultset
• Using extension methods ToArray, ToList,
  ToLookup, ToDictionary
• Using specific query operators, such as
  aggregates and set operators

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More on deferred execution

• Before execution queries can still be changed or
  expanded
• Adding additional sequence operators, such as
  Distinct, Skip, Take
• Manipulating expression tree
• Expression trees are immutable
• Reference assignments take deep tree copies

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Changes to way you write code

• Declarative
• Far less looping constructs visible
• Easier to read and to maintain
• Methods returning query or its results
• Remember deferred execution
• Force execution of query
• Hand over query for further manipulation
• Query reuse

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Linq and architecture
System.Data.Linq
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Architecture recommendations

• Find out where and how your queries execute
• Moment of execution
• Local versus remote execution
• Physical place/tier of query execution
• Keep queries inside assemblies
• Do not pass query expressions between layers
• Anonymous types shouldnt be return values
• Think about important types up front
• Use projections wisely

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Other recommendations

• Learn
• to write queries with and without keywords
• new language features
• Use whitepapers as reference
• Translation of query keywords to operators
• Evaluation details of operators
• Do not overuse or abuse var keyword
• Decreases readability and stops you from
  thinking if you know exact type, specify it
• It sometimes takes more keystrokes

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Runtimes and frameworks for Linq
providers

APIs
ADO.NET Entity Framework released out of
bounds with .NET FX 3.5
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Beyond .NET FX 3.5

• ADO.NET Entity Framework
• Microsofts long-term vision on data
• Brings query provider Linq to Entities
• Parallel Linq (PLinq)
• Passes parts of query to different cores in
  multicore/multiproc machine
• Community query providers for Linq
• Linq to Amazon, LDAP, SharePoint, NHibernate,
  MySql, Flickr, and more (to come)
• Linq 2.0

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Expanding on Linq

• Linq-enable your existing APIs
• Specifically for in-memory queries
• Create extension methods that return an
  IEnumerableltTgt object
• Write your own query provider
• Implement IQueryableltTgt
• Parse expression trees and translate nodes to
  different code or query language

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References

• Linq home page
• Future versions of
• C, Visual Basic, Visual Studio
• Recommended reading
• Linq to XML beta 1 docs
• Future Linq 2.0, PLinq
• Downloads
• Linq May 2006 CTP (for Visual Studio 2005)
• Visual Studio Orcas April 2007 Beta 1 and C, VB
  samples
• Reflector 5.0

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Blogs

• Microsoft Teams
• C
• VB
• ADO.NET
• Individuals on Linq
• General Oakleaf Systems, Wes Dyer, Jomo Fisher
• SQL Mike Taulty
• XML Eric White

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Summary

• Linq is about query keywords and operators
• Linq will change way you write your code
• Linq to XML might be more important than you
  think
• Is VB a better query language than C?
• Linq is extensible

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Questions?

• ?