LINQ Providers

1. LINQ Providers Or why .NET rules, and Java doesn’t Branimir Giurov SofiaDev.org UG Lead, C# MVP Freelance Software Developer www.sofiadev.org

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

3. typeof(linq)

4. <book> <title/> <author/> <year/> <price/> </book> Relational Objects XML C# 3.0 VB 9.0 Others… .NET Language Integrated Query LINQ toObjects LINQ toDatasets LINQ toSQL LINQ toEntities LINQ toXML

5. 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

6. 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

7. 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 };varlowNums =        from n in numbers        where n < 5        select n;Console.WriteLine("Numbers < 5:");foreach (var x in lowNums) {Console.WriteLine(x);    }}

8. 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 FK’s to query/modify data in SQL DB • Call SubmitChanges() when you’re done • Currently supports SQL 2000 & 2005 • System.Date.Linq.SqlClient.Sql2000Provider • System.Date.Linq.SqlClient.Sql2005Provider

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

10. 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

11. LINQ to XML • Combining it with other LINQ technologies makes life easier XElement xml = newXElement("contacts", newXElement("contact", newXAttribute("contactId", "2"), newXElement("firstName", "Barry"), newXElement("lastName", "Gottshall") ), newXElement("contact", newXAttribute("contactId", "3"), newXElement("firstName", "Armando"), newXElement("lastName", "Valdes") ) );

12. LINQ to XML • Result from previous example: <contacts> <contact contactId="2"> <firstName>Barry</firstName> <lastName>Gottshall</lastName> </contact> <contact contactId="3"> <firstName>Armando</firstName> <lastName>Valdes</lastName> </contact> </contacts>

13. LINQ to DataSet(s) • Allows developers to query existing DataSet sources within applications • Offline, still uses IQueryable<T> 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 -> DataTable -> LINQ Sequence support

14. How Does it Work? • Depends on if the type is {0} or not • IQueryable<T> • System.Linq.Queryable (System.Data.Linq.DataQuery<T>) • SQL • Entity • Datasets • The extension methods build an expression tree • If not, then check if it is a IEnumerable<T> • System.Linq.IEnumerable<T> • Objects • XML • The extension methods run the query

15. <book> <title/> <author/> <year/> <price/> </book> Relational Objects XML How Does it Work? C# 3.0 VB 9.0 Others… .NET Language Integrated Query LINQ toObjects LINQ toDatasets LINQ toSQL LINQ toEntities LINQ toXML

16. How Does it Work? • Extension methods for the from/select/where/groupby keywords • Lambda expressions • Expression tree for building & pre-compiling the statement that will run on a IQueryable<T> • p=> p.CompanyName.StartsWith(“A”) • Iterators for the in-memory queries (IEnumerable<T>) • foreach on an IEnumerable<T>

17. What’s Next? • PLINQ • Parallel FX Library • IParallelEnumerable<T> • CTP is available • Support for 3rd party DB engines