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TRANSCRIPT
Presented by,
MySQL & O’Reilly Media, Inc.
MySQL, LINQ and theADO.NET Entity Framework
Reggie Burnett, MySQL
David Sceppa, Microsoft
Agenda
From DataSets to data access layers Introducing LINQ Using LINQ to access your data The ADO.NET Entity Framework Introducing ADO.NET Data Services Summary
Working with DataSets
Basic example//Execute a query, retrieve and store the resultsconnectionString = "Data Source=localhost;User ID=...;";commandText = "SELECT CompanyName, City FROM Customers " + "WHERE Country = ?Country";adapter = new MySqlDataAdapter(commandText, connectionString);adapter.SelectCommand.Parameters.AddWithValue("?Country", "Brazil");table = new DataTable();adapter.Fill(table);
//Display the resultsDataGridView resultsGrid = new DataGridView();resultsGrid.DataSource = table;
//Submit pending changescommandBuilder = new MySqlCommandBuilder(adapter);adapter.Update(table);
Working with DataSets
Benefit• Rapid development - Designers, wizards,
bound controls make it easy to write code and generate user interface
Drawbacks• Developers must become SQL experts to
build advanced queries• Code becomes more complex when app
model and database schema diverge
Moving to data access layers
Focus on your application model• Queries expressed in terms of app model• Classes track their own changes
Data access layer responsible for• Translating into SQL queries• Returning results as objects• Submitting pending changes
Moving to data access layers
Basic example//Partial class to separate data access codepublic class Customer {
//Add methods to return data public static List<Customer> GetCustomers(string country) { List<Customer> results = new List<Customer> (); MySqlConnection connection = new MySqlConnection(connectString); connection.Open(); MySqlCommand command = new MySqlCommand(queryString, connection); command.Parameters.AddWithValue("?Country", country); MySqlDataReader reader = command.ExecuteReader(); while (reader.Read()) results.Add(Customer.CreateFromReader(reader)); return results; }
//Support tracking and submitting changes private string origCustomerId, origCompanyName, ...; public void SubmitChanges() { ... }}
Moving to data access layers
Benefit• Division of labor - Manage data access code
separately, only subset of developers need to become SQL gurus
Drawbacks• Data access code quickly gets complex
Classes that span multiple tables Handling inheritance hierarchies Note: Patterns and frameworks emerge
Introducing LINQ
What is LINQ?• Stands for Language INtegrated Query• Allows developers to query data structures
using SQL-like syntax from within their application’s code
• Is available to both C# and Visual Basic developers in Visual Studio 2008
Introducing LINQ
LINQ Example - Querying an array//Create an array of integersint[] myarray = new int[] { 49, 28, 20, 15, 25, 23, 24, 10, 7, 34 };
//Create a query for odd numbersvar oddNumbers = from i in myarray where i % 2 == 1 select i;
//Display the results of the queryforeach (int i in oddNumbers) Console.WriteLine(i);
//Create a query for odd numbers, sortedvar oddNumbers = from i in myarray where i % 2 == 1 orderby i select i;
//Create a query for odd numbers, sorted in descending ordervar oddNumbers = from i in myarray where i % 2 == 1 orderby i descending select i;
//Create a query for odd numbersvar oddNumbers = from i in myarray where i % 2 == 1 select i;
//Compose the original query to create a query for odd numbersvar sorted = from i in oddNumbers orderby i descending select i;
LINQ-enabled classes
Collection classes extended• Arrays, Hashtable, List<T>, etc. LINQ to DataSet• Extended for untyped and strongly typed LINQ to XML Data access technologies• LINQ to SQL• LINQ to Entities
Agenda
From DataSets to data access layers Introducing LINQ Using LINQ to access your data The ADO.NET Entity Framework Introducing ADO.NET Data Services Summary
LINQ to DataSet
DataSet class enhanced to support LINQ• Available via typed and untyped DataSet
Dim ordersQuery = From o In dataSet.Orders _ Where o.CustomerID = "ALFKI" _ Select o
For Each o As NorthwindDataSet.OrdersRow In ordersQuery Console.WriteLine("{0} {1,10:d}", _ o.OrderID, o.OrderDate) Next o
LINQ to DataSet
Benefits• Quickest way to use LINQ w/ .NET 2.0
feature set• Supports query capabilities previously
unavailable using a DataSet• Returns results as series of DataRows or as
anonymous types Limitations
• All client-side processing
Benefits• Rapid application development scenarios• Query processing performed at the server• Designer makes mapping classes to tables
simple Limitations
• Supports limited mapping scenarios• No provider model for extensibilityNo provider model for extensibility
LINQ to SQL
Benefits• Rapid application development scenarios• Query processing performed at the server• Designer makes mapping classes to tables
simple Limitations
• Supports limited mapping scenarios
Agenda
From DataSets to data access layers Introducing LINQ Using LINQ to access your data The ADO.NET Entity Framework Introducing ADO.NET Data Services Summary
What is LINQ to Entities?• LINQ implementation of the Entity Data Model
What is the Entity Data Model?• Definition for your application model• Map between app model, database schema• Advanced mapping scenarios supported One entity mapped across multiple tables Multiple inheritance hierarchy mappings Many-to-many without "link" table in model
What is LINQ to Entities?• LINQ implementation of the Entity Data Model
LINQ to Entities
LINQ to DataSet
DataSet class enhanced to support LINQ• Available via typed and untyped DataSet
Dim ordersQuery = From o In dataSet.Orders _ Where o.CustomerID = "ALFKI" _ Select o
For Each o As NorthwindDataSet.OrdersRow In ordersQuery Console.WriteLine("{0} {1,10:d}", _ o.OrderID, o.OrderDate) Next o
LINQ to Entities or LINQ to SQL? LINQ to SQL
• Shipped with Visual Studio 2008 and .NET 3.5
• Emphasis on rapid application development
• Supports Microsoft SQL Server family of databases
LINQ to Entities• Will ship as an update to .NET 3.5
• Offers a provider model for third-party databases
• Designed for enterprise-grade data scenarios
• Higher level of abstraction for programming databases
• Just one layer of the overall ADO.NET Entity Framework
LINQ to Entities: Generating Queries
Converting LINQ queries to SQL• Compiler converts code into a LINQ expression tree• LINQ to Entities converts LINQ expression tree into
a DbCommandTree based on mapping information DbCommandTree expressed in terms of the
database schema• ADO.NET provider generates a DbCommand• LINQ to Entities executes the DbCommand,
assembles results into the structure(s) specified in the LINQ query
Agenda
From DataSets to data access layers Introducing LINQ Using LINQ to access your data The ADO.NET Entity Framework Introducing ADO.NET Data Services Summary
Entity Framework: LINQ and more
ADO.NET Entity Framework Layers• First implementation of
Entity Data Model (EDM)
• Includes a text-based queryquery language (Entity SQL)
• New Provider – EntityClient
• New ORM stack (Object Services) leverages Entity Client
• LINQ support over Entities
• An evolution of ADO.NET preserving customer investment
ADO.NET ProviderADO.NET Provider
EntityClientEntityClient
ObjectServicesObjectServices
LINQ to EntitiesLINQ to Entities
Entity Framework Query Options
LINQ to Entities
Sweet spot:• Strongly typed queries and results Compile-time type checking and Intellisense
• Results returned as objects: entities / projections• Queries must be well defined at compile time
var ordersQuery = from o in context.Orders where o.Customers.CustomerID == "ALFKI" select o;
foreach (var o in ordersQuery) Console.WriteLine("{0} {1:d}", o.OrderID, o.OrderDate);
Entity Framework Query Options
ObjectQuery<T> / ObjectQuery(Of T)
Sweet spot:• Strongly typed results, text-based queries• Results returned as objects: entities / projections• Queries more loosely defined at compile-time
Dim eql As String = "SELECT VALUE o FROM Orders AS o " & _ " WHERE o.Customer.CustomerID = 'ALFKI'"Dim ordersQuery = context.CreateQuery(Of Order)(esql)
For Each o As Order In ordersQuery Console.WriteLine("{0} {1,10:d} ", o.OrderID, o.OrderDate)Next o
Entity Framework Query Options
EntityClient Provider
Sweet spot:• Untyped queries and results• Results returned as DataReaders• Queries can be generated purely at run time No application model classes needed at compile time
string eSql = "SELECT VALUE o FROM NorthwindEntities.Orders AS o " + "WHERE o.Customers.CustomerID = 'ALFKI'";EntityCommand cmd = new EntityCommand(eSql, connectionString);EntityDataReader rdr = cmd.ExecuteReader();while (rdr.Read()) Console.WriteLine("{0} {1:d}", rdr["OrderID"], rdr["OrderDate"]);
Agenda
From DataSets to data access layers Introducing LINQ Using LINQ to access your data The ADO.NET Entity Framework Introducing ADO.NET Data Services Summary
ADO.NET Data Services
Formerly known as "Project Astoria"• Part of ASP.NET Extensions Preview• Integrated into .NET Framework going forward
Targeting Web development technologies• Silverlight and AJAX• Data returned via Web-friendly formats ATOM (XML-based) and JSON
ADO.NET Data Services
Service exposed via lightweight data access API• Supply both location and query as a URI: http://myserver/data.svc/Customers[ALFKI]/Orders
• Query converted to LINQ inside of service• Supports submitting changes Specialized Entity Framework logic for submitting changes
Online data hosting service available For more information:• http://astoria.mslivelabs.com
Agenda
From DataSets to data access layers Introducing LINQ Using LINQ to access your data The ADO.NET Entity Framework Introducing ADO.NET Data Services Summary
Summary - LINQ
Represents a revolution for developers• Query your objects using SQL-like syntax• LINQ to DataSet Rich query scenarios for data residing in a DataSet
• LINQ to Entities Provider model for working with other data stores Supports enterprise mapping scenarios
Summary - ADO.NET Entity Framework
More than just LINQ to Entities• Also supports text-based query language – ESQL• ObjectQuery<T> for strongly typed results• EntityClient for reader-based results
Enterprise-grade data scenarios Provider model for working with other data stores
Summary - ADO.NET Data Services
Designed for Silverlight, AJAX environments Lightweight API, connect and query via URI Retrieve results via familiar formats• ATOM• JSON
Questions?