LINQ to SQL

Introduction I t d ti To T LINQ This material is based on the original slides of John Hidey, Mike Bird, Sharp Dudes, LLC

Data Access Data != Objects (Object Relational Mapping)

Build database-like search functionality into the y data: object, j , .NET Framework that works on any XML, SQL, custom types… LINQ: Language INtegrated Query

C# 3.0 Language Innovations

Local variable ttype inference i f

var contacts = Query from c in customers expressions where c.State == "WA" select new { c.Name, c.Phone }; Lambda expressions

var contacts t t = customers .Where(c ( => c.State == "WA")) .Select(c => new { c.Name, c.Phone }); Extension methods

Anonymous types

Object initializers

LINQ Q To Objects j Restriction

Where

Projection

Select, SelectMany

Ordering

OrderBy, ThenBy

Grouping

GroupBy

Joins

Join, GroupJoin

Quantifiers

Any, All

Partitioning

Take Skip, Take, Skip TakeWhile, TakeWhile SkipWhile

Sets

Distinct, Union, Intersect, Except

Elements

First, Last, Single, ElementAt

Aggregation

Count, Sum, Min, Max, Average

Conversion

ToArray, ToList, ToDictionary

Casting

OfType, Cast

LINQ Basics Š Query Operators can be used against any .NET collection (IEnumerable) „ „

Built in examples: Select Built-in Select, Where Where, GroupBy GroupBy, Join, Join etc. etc Extensibility model supports adding/replacing them

Š Query Expressions can operate on information sources and apply query operators against them to return IEnumerable sequences

LINQ to SQL Š Language integrated data access „ „

Maps tables and rows to classes and objects Builds on ADO ADO.NET NET and .NET NET Transactions

Š Mapping „ „

Encoded in attributes or external XML file Relationships map to properties

Š Persistence „ „

Automatic change tracking Updates through SQL or stored procedures

LINQ to SQL A Accessing i data d t today t d SqlConnection c = new SqlConnection(…); c.Open(); SqlCommand q cmd = new SqlCommand( q ( @"SELECT c.Name, c.Phone FROM Customers c WHERE c.City = @p0"); cmd Parameters AddWithValue("@p0" cmd.Parameters.AddWithValue( @p0 , "London“); London ); DataReader dr = c.ExecuteReader(cmd); while (dr.Read()) { string name = dr.GetString(0); string phone = dr.GetString(1); DateTime date = dr.GetDateTime(2); } dr Close(); dr.Close();

Queries in quotes

Loosely bound arguments

Loosely typed result sets

No compile time checks

LINQ to SQL Accessing A i data d t with ith LINQ 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 };

Classes describe data Tables are like collections Strongly typed connections I t Integrated t d query syntax Strongly St l typed t d results

LINQ to SQL Mapping Database

DataContext

Table

Class

View

Class

Column

Field / Property

Relationship

Field / Property

Stored Proced Procedure re

Method

LINQ to SQL Architecture from c in db.Customers where c.City == "London" select c.CompanyName

LINQ Query

Application

Objects

db.Customers.Add(c1); c2.City = “Seattle"; db.Customers.Remove(c3);

SubmitChanges()

LINQ to SQL SQL Query

Rows

SELECT CompanyName FROM Cust WHERE City = 'London'

DML or SProcs INSERT INTO Cust … UPDATE Cust … DELETE FROM Cust …

SQL Server

Key Points Š Flexible Fl ibl mapping i „

“Classes first” or “data first”, attributes or mapping file

Š DataContext „

Strongly typed database connection

Š Entity classes „

Identity mapping and change tracking

Š Relationships „

One-to-one, one-to-many

LINQ to SQL Š Access relational data as strongly typed objects Š Language L iintegrated t t d query Š Works with existing infrastructure Š Unified query and transform of objects, relational, XML

Resources Š The LINQ Project on MSDN (http://msdn2.microsoft.com/enus/netframework/aa904594.aspx) Š Charlie Calvert’s Blog (http://blogs.msdn.com/charlie/) Š Mike Taulty’s Blog (http://mtaulty.com/) Š LINQ in Action (http://linqinaction.net/) Š Scott Gu’s Blog (http://weblogs.asp.net/scottgu/default.aspx)