LINQ Providers

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LINQ Providers
Or why .NET rules, and Java doesnt
Branimir Giurov
SofiaDev.org UG Lead, C MVP Freelance Software
Developer
www.sofiadev.org
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Contents

• typeof(linq)
• How does it work?
• Lambda, extension methods, iterators

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typeof(linq)
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C 3.0
VB 9.0
Others
.NET Language Integrated Query
LINQ toObjects
LINQ toSQL
LINQ toXML
LINQ toEntities
LINQ toDatasets
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typeof(linq)

• LINQ to Objects
• LINQ to SQL
• LINQ to XML
• LINQ to Datasets
• LINQ to Entities
• LINQ to Windows Search
• LINQ to Google
• LINQ to Sharepoint
• LINQ to nHibernate

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LINQ to Objects

• Query language over collections of objects
• Standard SQL-like set of query operators,
  including joins and grouping
• New query operators can be added, fully
  extensible (extension methods)
• Intellisense and compiler syntax checking support
  in Visual Studio

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LINQ to Objects

• How to query an array of int?

public void Linq1()     int numbers 5, 4,
1, 3, 9, 8, 6, 7, 2, 0     var lowNums
        from n in numbers        where n lt
5        select n    Console.WriteLine("Number
s lt 5")    foreach (var x in lowNums)
        Console.WriteLine(x)    
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LINQ to SQL

• Write queries in any .NET language to retrieve
  and manipulate data from SQL
• Use FK constraints for defining relations of data
  without joins
• Join in code on any column that has no FK defined
• Use FKs to query/modify data in SQL DB
• Call SubmitChanges() when youre done
• Currently supports SQL 2000 2005
• System.Date.Linq.SqlClient.Sql2000Provider
• System.Date.Linq.SqlClient.Sql2005Provider

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DEMO
LINQ to SQL ToString() Modifying Queries Mapping
Styles Mapping Tools
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LINQ to XML

• LINQ to XML is a new way to construct, write and
  read XML data in the .NET language of the
  developers choice
• Simplifies working with XML
• No more XPath or XSLT
• Not a replacement for DOM or any of the current
  XML libs
• Supports writing Query Expressions
• Can be combined with any of the other LINQ
  technologies
• Supports SAX-style reading/writing of documents
  with the use of XStreamingElement
• Differed execution

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LINQ to XML

• Combining it with other LINQ technologies makes
  life easier

XElement xml new XElement("contacts", new
XElement("contact", new XAttribute("contactId"
, "2"), new XElement("firstName",
"Barry"), new XElement("lastName",
"Gottshall") ), new XElement("contact", new
XAttribute("contactId", "3"), new
XElement("firstName", "Armando"), new
XElement("lastName", "Valdes") ) )
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LINQ to XML

• Result from previous example

ltcontactsgt ltcontact contactId"2"gt
ltfirstNamegtBarrylt/firstNamegt
ltlastNamegtGottshalllt/lastNamegt lt/contactgt
ltcontact contactId"3"gt ltfirstNamegtArmandolt/fi
rstNamegt ltlastNamegtValdeslt/lastNamegt
lt/contactgt lt/contactsgt
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LINQ to DataSet(s)

• Allows developers to query existing DataSet
  sources within applications
• Offline, still uses IQueryableltTgt approach
• 2 types of queries, depending on use of
  typed/un-typed datasets
• Use LINQ in current applications without
  re-writing using LINQ to SQL
• Bi-directional LINQ Sequence -gt DataTable -gt
  LINQ Sequence support

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How Does it Work?

• Depends on if the type is 0 or not
• IQueryableltTgt
• System.Linq.Queryable (System.Data.Linq.DataQuerylt
  Tgt)
• SQL
• Entity
• Datasets
• The extension methods build an expression tree
• If not, then check if it is a IEnumerableltTgt
• System.Linq.IEnumerableltTgt
• Objects
• XML
• The extension methods run the query

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How Does it Work?
C 3.0
VB 9.0
Others
.NET Language Integrated Query
LINQ toObjects
LINQ toSQL
LINQ toXML
LINQ toEntities
LINQ toDatasets
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How Does it Work?

• Extension methods for the from/select/where/groupb
  y keywords
• Lambda expressions
• Expression tree for building pre-compiling the
  statement that will run on a IQueryableltTgt
• pgt p.CompanyName.StartsWith(A)
• Iterators for the in-memory queries
  (IEnumerableltTgt)
• foreach on an IEnumerableltTgt

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Whats Next?

• PLINQ
• Parallel FX Library
• IParallelEnumerableltTgt
• CTP is available
• Support for 3rd party DB engines