LINQ, DLINQ and XLINQ : LINQ, DLINQ and XLINQ Harjeet Singh C# 3.0
What is LINQ? : What is LINQ? “Language Integrated Query”
Evolution of application data management
Coming with C# 3.0 and VB.NET 9.0
Goals
Provide overview of the LINQ project
Point out learning resources for self study
Next week - LINQ practical
Anders Hejlsberg Don Box
Philosophy of C# 3.0 And LINQ : Philosophy of C# 3.0 And LINQ Integrates
object,
relational
semi-structured data models.
By generalization, rather than by ad-hoc specializations
Similar to database systems which now integrate
the relational and XML data model
SQL and XQuery.
The Problem : The Problem Worlds of OO and data access are far, far apart
OO language types and native database types are often different
SQL code is “inside the quotes”
No strong typing or compile-time type checking
No Intellisense
No Statement completion
SQL and XML have query languages, objects to not
LINQ seeks to bridge the gap
What is LINQ? : What is LINQ? Standard Query Operators DLinq (ADO.NET) XLinq
(System.Xml) .NET Language Integrated Query C# VB Others… Source: Anders Hejlsberg’s PDC Presentation
Standard Query Operators : Standard Query Operators Source: Anders Hejlsberg’s PDC Presentation
DLinq : DLinq A means of managing relational data SqlConnection c = new SqlConnection(…);
c.Open();
SqlCommand cmd = new SqlCommand(
@"SELECT c.Name, c.Phone
FROM Customers c
WHERE c.City = @p0");
cmd.Parameters.AddWithValue("@p0", "London“);
DataReader dr = c.Execute(cmd);
while (dr.Read()) {
string name = dr.GetString(0);
string phone = dr.GetString(1);
DateTime date = dr.GetDateTime(2);
}
dr.Close(); Accessing data today: Queries in quotes Loosely bound arguments Loosely typed result sets No compile time checks
DLinq : DLinq public class Customer { … }
public class Northwind: DataContext
{
public Table Customers;
…
} Northwind db = new Northwind(…);
var contacts =
from c in db.Customers
where c.City == "London"
select new { c.Name, c.Phone }; Accessing data with DLinq Classes describe data Strongly typed connection Integrated query syntax Strongly typed results Tables are like collections
DLinq : DLinq Language integrated data access
Maps tables and rows to classes and objects
Builds on ADO.NET and .NET Transactions
Mapping
Encoded in attributes
Relationships map to properties
Persistence
Automatic change tracking
Updates through SQL or stored procedures
XLinq : XLinq XmlDocument doc = new XmlDocument();
XmlElement contacts = doc.CreateElement("contacts");
foreach (Customer c in customers)
if (c.Country == "USA") {
XmlElement e = doc.CreateElement("contact");
XmlElement name = doc.CreateElement("name");
name.InnerText = c.CompanyName;
e.AppendChild(name);
XmlElement phone = doc.CreateElement("phone");
phone.InnerText = c.Phone;
e.AppendChild(phone);
contacts.AppendChild(e);
}
doc.AppendChild(contacts);
Programming XML today
Great Lakes Food
(503) 555-7123
…
Imperative model Document centric No integrated queries Memory intensive
XLinq : XLinq XElement contacts = new XElement("contacts",
from c in customers
where c.Country == "USA"
select new XElement("contact",
new XElement("name", c.CompanyName),
new XElement("phone", c.Phone)
)
); Programming XML with XLinq Declarative model Element centric Integrated queries Smaller and faster
XLinq : XLinq Language integrated query for XML
Expressive power of XPath / XQuery
But with C# or VB as programming language
Leverages experience with DOM
Element centric, not document centric
Functional construction
Text nodes are just strings
Simplified XML namespace support
Faster and smaller
What is LINQ? : What is LINQ? The LINQ project is:
Language Integrated Query for .NET
Native query syntax for .NET languages
Standard Query Operators
SQL-like method extensions for any .NET collection
System.Query namespace
DLinq
Code name for future version of ADO.NET
Query enabled data access framework
System.Data.Xlinq namespace
XLinq
Query enabled, smaller, faster XML DOM
System.XML.Xlinq namespace
Benefits of LINQ : Benefits of LINQ Unified querying of objects, relational, XML
Type checking and IntelliSense for queries
SQL and XQuery-like power in C# and VB
Extensibility model for languages / APIs
Resources : Resources LINQ Project Home Page
http://msdn.microsoft.com/data/ref/linq/
Anders Hejlsberg – LINQ
http://channel9.msdn.com/showpost.aspx?postid=114680
LINQ Project Overview Whitepaper
http://msdn.microsoft.com/data/ref/linq/default.aspx?pull=/library/en-us/dndotnet/html/linqprojectovw.asp