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Microsoft LINQ

Microsoft LINQ. Ryan Wiederholt. Agenda. Introduction What is LINQ Syntax How to Query Example Program. Introduction. Language INtegrated Query Released as a part of the .Net Framework 3.5 November 19, 2007 Supported in the .Net languages C#, VB.Net. What is LINQ?.

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Microsoft LINQ

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  1. Microsoft LINQ Ryan Wiederholt

  2. Agenda • Introduction • What is LINQ • Syntax • How to Query • Example Program

  3. Introduction • Language INtegrated Query • Released as a part of the .Net Framework 3.5 • November 19, 2007 • Supported in the .Net languages • C#, VB.Net

  4. What is LINQ? • Used as a universal query language for retrieving data from containers • Appropriate data containers include: • Arrays • .Net containers such as List and Dictionary • Any IEnumerable collection • SQL Server Database • XML Document

  5. Syntax • Resembles SQL in reverse • Introduces new variable type “var” • Compiler determines the type • Still considered strongly typed • Creates “anonymous type” if data type cannot be determined

  6. Syntax • Retrieves all integers from listInteger • listInteger is an array of integers • allInt will be an IEnumerable<int> type from statement creates local instance of listInteger in l varallInt = from l in listInteger select l; results of query stored in allInt Select statement specifies what data to take

  7. Syntax: Filtering • Retrieves all integers from listInteger that are greater than 5 • Statements between the from statement and select statement are used to refine results returned vargreaterThanFive = from l in listInteger where l > 5 select l;

  8. Syntax: Other Common Operations • join • orderby … acsending • orderby … decending • group • count • min • Plus many more…

  9. Syntax: Alternate Query Forms • Using lambda expressions and functions: • varfirstPosInt = allInts.First(a => a >= 0); • varposInt = (allInts.Where(a => a >= 0).Select(a => a);

  10. How to Query with LINQ • 3 steps in a LINQ query operation: • Obtain the data source • Create the query • Execute the query

  11. Obtain the Data Source • Data Sources can be in memory containers, SQL Server databases or XML documents • In memory data sources need no additional preparation after they have been created • SQL Server Databases must be set up using the DBML Designer in Visual Studio • XML documents must be loaded into an XDocument object

  12. SQL Server Database: DBML Designer • Add new LINQ to SQL Class to project • Connect to Database using Server Explorer • Drag tables over to designer pane • Relationships will be set up automatically

  13. SQL Server Database: DataContext • DataContext will be generated from the DBML diagram • Create DataContext object in code • Name Format: “[NameOfDBMLFile]DataContext” MyDatabaseDataContextAWDatabse = new MyDatabaseDataContext(); //Put query here

  14. XML Documents: • Create new XDocument object from XML File: XDocument xml = XDocument.Load(@”C:\Users\Example\myXmlDoc.xml”);

  15. Next Step: Create the Query • Syntax is constant for all types of data sources • When querying XML files • Use Elements() and Element() methods to specify tags to query • From x in xmlObject.Elements(“TopTag”) order by (int)x.Element(“id”) select x;

  16. Final Step: Execute the Query • Query is not executed until the variable is used in code • foreach loop is a common way of accessing query results • Use methods to grab specific elements • Takes first item returned from the query allInt • intfirstInt = allInt.First();

  17. Review • Universal syntax when querying in memory data, SQL Servers, or XML files • Syntax resembles SQL • Features make coding quicker and less prone to errors

  18. References • Microsoft Corporation. LINQ (Language-Integrated Query). Retrieved October 5, 2013 from http://msdn.microsoft.com/en-us/library/vstudio/bb397926.aspx • Ferracchiati, F. LINQ for Visual C# 2008. New York, NY: Spinger-Verlag New York Inc, 2008. • Russo, Marco, and Paolo Pialorsi. Introducing Microsoft LINQ. Redmond, WA: Microsoft, 2007.   • Guthrie, Scott. "Using LINQ to SQL (part 1)." ScottGu's Blog. Microsoft, 19 May 2007. Web. 5 Oct. 2013. • AdventureWorks2008R2 Database and ObjectDumper Class courtesy of Microsoft • AdventureWorks2008R2 available at http://msftdbprodsamples.codeplex.com/releases/view/93587 • ObjectDumper available in this package at http://code.msdn.microsoft.com/csharpsamples/Release/ProjectReleases.aspx?ReleaseId=8

  19. Sample Code • Entire project is in compressed file. • Some code is commented out due to needing SQL Express installed and the proper database (which is too large to embed here)

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