The LINQ Project
C# VB Others…
.NET Language Integrated Query
Standard
DLinq XLinq
Query
(ADO.NET) (System.Xml)
Operators
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Objects SQL WinFS XML

Language Integrated Query
2

How does it work?
Standard query operators
Query expressions
Extension methods
Lambda expressions
Expression trees
Local variable type inference
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C# 3.0 Language Innovations
Query
var contacts = expressions
from c in customers
where c.State == "WA"
Local variable select new { c.Name, c.Phone };
type inference
Lambda
expressions
var contacts =
customers
.Where(c => c.State == "WA")
.Select(c => new { c.Name, c.Phone });
Extension
methods Anonymous Object
types initializers
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Lambda Expressions and
Extension Methods
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Object Initializers
Embedded
public class Rectangle objects
{
private Point p1 = new Point();
private Point p2 = new Point(); Read-only
properties
public Point P1 { get { return p1; } }
public Point P2 { get { return p2; } }
}
Rectangle r = new Rectangle {
P1 = { X = 0, Y = 1 },
P2 = { X = 2, Y = 3 } No “new Point”
};
Rectangle r = new Rectangle();
r.P1.X = 0;
r.P1.Y = 1;
r.P2.X = 2;
r.P2.Y = 3;
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Local Variable Type Inference
int i = 5;
string s = "Hello";
double d = 1.0;
int[] numbers = new int[] {1, 2, 3};
Dictionary<int,Order> orders = new Dictionary<int,Order>();
var i = 5;
var s = "Hello";
var d = 1.0;
var numbers = new int[] {1, 2, 3};
var orders = new Dictionary<int,Order>();
“var” means same
type as initializer
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Anonymous Types
public class Customer
{
public string Name;
public Address Address; public class Contact
public string Phone; { class ???
public List<Order> Orders; public{string Name;
… public string Phone; Name;
public string
} } public string Phone;
Customer c = GetCustomer(…); }
Contact x = new Contact { Name = c.Name, Phone = c.Phone };
Customer c = GetCustomer(…);
var x = new { Name = c.Name, Phone = c.Phone };
Projection style
Customer c = GetCustomer(…); initializer
var x = new { c.Name, c.Phone };
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Query Expressions
Language integrated query syntax
Starts with
from Zero or more
from or where
from id in source
{ from id in source | where condition } Optional
[ orderby ordering, ordering, … ] orderby
select expr | group expr by key
[ into id query ] Ends with select
Optional into or group by
continuation
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Query Expressions
Queries translate to method invocations
Where, Select, SelectMany, OrderBy, GroupBy
from c in customers
where c.State == "WA"
select new { c.Name, c.Phone };
customers
.Where(c => c.State == "WA")
.Select(c => new { c.Name, c.Phone });
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C# 3.0 Language Innovations
c => c.Name
Lambda expressions
Extension methods static void Dump(this object o);
Local variable type inference var x = 5;
Object initializers new Point { x = 1, y = 2 }
Anonymous types new { c.Name,
c.Phone }
Query expressions
from … where …
Expression trees select
Expression<T>
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Standard Query Operators
Restriction Where
Projection Select, SelectMany
Ordering OrderBy, ThenBy
Grouping GroupBy
Quantifiers Any, All
Partitioning Take, Skip, TakeWhile, SkipWhile
Sets Distinct, Union, Intersect, Except
Elements First, FirstOrDefault, ElementAt
Aggregation Count, Sum, Min, Max, Average
Conversion ToArray, ToList, ToDictionary
Casting OfType<T>
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Deferred Query Execution
Customer[] custs = SampleData.GetCustomers();
var query = from c in custs where c.City == "London" select c.Name;
var query = custs.Where(c => c.City == "London").Select(c => c.Name);
string[] names = query.ToArray();
custs names
ID Name Phone
Where Select
c => c.City == "London" c => c.Name
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DLinq For Relational Data
Accessing data today
Queries in
SqlConnection c = new SqlConnection(…); quotes
c.Open();
SqlCommand cmd = new SqlCommand(
@"SELECT c.Name, c.Phone Loosely bound
FROM Customers c arguments
WHERE c.City = @p0");
cmd.Parameters.AddWithValue("@p0", "London“);
DataReader dr = c.Execute(cmd);
while (dr.Read()) { Loosely typed
string name = dr.GetString(0); result sets
string phone = dr.GetString(1);
DateTime date = dr.GetDateTime(2);
}
dr.Close(); No compile
time checks
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DLinq For Relational Data
Accessing data with DLinq
Classes
public class Customer { … } describe data
public class Northwind: DataContext
{ Tables are like
public Table<Customer> Customers; collections
…
}
Strongly typed
connection
Northwind db = new Northwind(…);
var contacts =
from c in db.Customers Integrated
where c.City == "London" query syntax
select new { c.Name, c.Phone };
Strongly typed
results
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DLinq For Relational Data
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
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XLinq For XML Data
Programming XML today Imperative
model
XmlDocument doc = new XmlDocument();
XmlElement contacts = doc.CreateElement("contacts"); Document
foreach (Customer c in customers) centric
if (c.Country == "USA") {
XmlElement e = doc.CreateElement("contact");
XmlElement name = doc.CreateElement("name"); No integrated
name.InnerText = c.CompanyName; queries
e.AppendChild(name);
XmlElement phone = doc.CreateElement("phone");
phone.InnerText = c.Phone; Memory
e.AppendChild(phone); <contacts> intensive
contacts.AppendChild(e); <contact>
<name>Great Lakes Food</name>
} <phone>(503) 555-7123</phone>
doc.AppendChild(contacts); </contact>
…
</contacts>
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XLinq For XML Data
Programming XML with XLinq
Declarative
model
XElement contacts = new XElement("contacts",
from c in customers
where c.Country == "USA" Element
select new XElement("contact", centric
new XElement("name", c.CompanyName),
new XElement("phone", c.Phone)
Integrated
)
queries
);
Smaller and
faster
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XLinq For XML Data
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
19

The LINQ Project
Language Integrated Query for .NET
Native query syntax in C# 3.0 and VB 9.0
Standard Query Operators
SQL-like queries for any .NET collection
DLinq
Query enabled data access framework
XLinq
Query enabled, smaller, faster XML DOM
20

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
21