Entity Framework Overview
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This document discusses the evolution of data access from 1990 to 2010, focusing on object-relational mapping (ORM) techniques. It provides an overview of ORM as an abstraction technique for working with relational data as objects. The document outlines several ORM options available for .NET developers and describes Microsoft's strategic ORM technologies - LINQ to SQL and the ADO.NET Entity Framework. It provides details on Entity Framework's Entity Data Model and how to consume an EDM to query and manage data.
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Entity Framework Overview
- 1. Eric Nelson Developer & Platform Group Microsoft Ltd eric.nelson@microsoft.com http://geekswithblogs.net/IUpdateable http://twitter.com/ericnel
- 2. Accessing data in 1990 • ODBC, embedded SQL Accessing data in 2000 • ADO, Stored Procedures Accessing data in 2005 • ADO.NET, Datasets, DataReaders Accessing data in 2010 • ORM baby!
- 3. What is it? an Abstraction technique for working with relational tables as if they were objects in memory Intention is to hide away the complexity of the underlying tables and give a uniform way of working with data Why use it? Developer productivity Retain database independence Note: Using an ORM does not mean you must use the ORM!
- 4. Many ORMs out there LLBLGen Pro http://www.llblgen.com/ Nhibernate http://www.hibernate.org/343.html EntitySpaces http://www.entityspaces.net/Portal/Default.aspx Open Access http://www.telerik.com/products/orm.aspx DevForce http://www.ideablade.com/ XPO http://www.devexpress.com/Products/NET/ORM/ Lightspeed http://www.mindscape.co.nz/products/LightSpeed/default.aspx Plus many, many more No clear “winner” = relatively little adoption of ORM Developers waiting on Microsoft Of 31 .NET ORMs in 2003, 9 lasted to 2008
- 5. Typed Datasets (cough) – shipped ObjectSpaces “v1” – never shipped ObjectSpaces “v2” – never shipped Microsoft Business Framework – never shipped WinFS – never shipped LINQ to SQL - shipped November 2007 Visual Studio 2008 & .NET Framework 3.5 LINQ to Entities - shipped August 2008 Visual Studio 2008 SP1 & .NET Framework 3.5 SP1 Note: LINQ to Entities is the most visible part of the ADO.NET Entity Framework
- 6. Entity Framework and LINQ to Entities is our strategic technology Entity Framework v2 in VS2010 and .NET Framework 4.0 Best of LINQ to SQL moves into LINQ to Entities Microsoft is using it Data Services - shipping Reporting Services Microsoft “M” Partners supporting it Database Vendors – IBM,OpenLink, Data Direct, Devart etc ORM vendors supporting it DevForce now target Entity Framework, replacing their own LLBLGen v3 will target Entity Framework as well as their own It is not just about ORM
- 7. What is LINQ? LINQ is not about databases, it is about objects LINQ = Language-Integrated Query Extensions to programming languages to query objects in memory Why use it? Productivity!!! LINQ rocks www.linqpad.net We ship LINQ to Objects LINQ to XML LINQ to Datasets LINQ to SQL – just SQL Server LINQ to Entities – added in .NET Framework 3.5 SP1 Others make LINQ to Flickr etc
- 8. { Simple Walkthough }
- 9. LINQ to SQL LINQ to Entities Database Support SQL Server SQL Server, DB2, Oracle, Sybase, MySQL ... Object Relational Simple Complex Mapping Capabilities Not strategic Status Strategic Often Annoying Rarely
- 10. Entity Framework is not just about ORM Entity Framework v1 is being adopted Typically on applications expected to “live” a long time Entity Framework is only .NET 3.5 SP1 and above Entity Framework is probably not the best choice for a “short lived” SQL Server applications Entity Framework v1 has “warts” Designer It is annoying – buggy, clunky Exposes subset of the functionality Does not support model first N-tier story Stored Procedure Support Foreign Keys PoCo Guids SQL 2008 New Types
- 11. “EF is still cutting development time “the entity framework in half. Ya gotta can kiss my damn love it.” ass - this shit is ridiculous”
- 13. What is it? Tools and services to create an Entity Data Model EDM gives ORM to SQL Server, Oracle, DB2 etc Tools and services for consuming an Entity Data Model Why use it? Productivity Complex mapping between entities and database tables Works great with ADO.NET Data Services Notes Strategic but just released...
- 14. Entity Data Model Application model Mapped to a persistence store Conceptual Comprised of three layers: Conceptual (CSDL) Mapping (MSL) Mapping Storage (SSDL) Database agnostic Comprised of: Storage Entities Associations Functions
- 15. { A look at mapping }
- 16. 2 1 The ORM - optional Object Services 3 Entity Client
- 17. Familiar ADO.NET object model: EntityCommand EntityConnection EntityDataReader EntityParameter EntityTransaction Text-based results Read-only Uses Entity SQL
- 18. Queries materialized as Objects ObjectContext ObjectQuery<T> Built on top of Entity Client Two query options: Entity SQL LINQ Runtime services: Unit of work Identity tracking Eager/explicit loading
- 19. { Consuming an EDM}
- 20. ORM is an abstraction layer about data • Productivity • Database Independence Microsoft has two ORMs • LINQ to SQL – only SQL Server • Entity Framework (includes LINQ to Entities) – many RDBMS, strategic ADO.NET Entity Framework includes all the other bits • EDM, Linq to Entities, ESQL, Object Services • Part of .NET Framework 3.5 SP1 Entity Data Model – mapping from conceptual to store • CSDL = Conceptual Schema Definition Language • SSDL = Store Schema Definition Language • MSDL = Mapping Schema Definition Language Two query languages • ESQL = Entity SQL. Read only query language similar to SQL • LINQ to Entities = Language Integrated Query to the EDM
- 21. • .NET Framework 4.0 Entity Framework v2 • http://blogs.msdn.com/efdesign Entity Framework • Across MS Products and Technologies more widely adopted • Reporting Services vNext • Better ORM capabilities in LINQ to Entities Rough edges • POCO support, N-Tier, Model First removed Technologies work • e.g. ASP.NET Dynamic Data and Entity Framework better together • Less xml editing during development Better tooling
- 22. 1990 to • Data Access technology remained reasonably static 2007 - • Procedural, API access • Surfaced the database schema Tables • No clear ORM choice • LINQ – excellent addition to the .NET 2008 – languages • Entity Framework and the EDM – strategic Objects investment • Productivity leap
- 24. © 2008 Microsoft Ltd. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries. The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.
Editor's Notes
- Estimated Time: 6 minutesTalking Points: When we talk about the Entity Framework, we’re actually talking about two things: The Entity Data Model (EDM) The Entity Framework It’s important to delineate the two as separate, but complementing technologies The EDM is a set of layers that make up your application’s model, as well as it’s mapping to an underlying data store. Made up of three files: CSDL (Conceptual Schema Definition Language) MSL (Mapping Specification Language) SSDL (Storage Schema Definition Language) This separation of concerns allows great flexibility: Model your application the way you want regardless of the state/structure of its underlying data store Normalize your database as much as you need without worrying about affecting the interface of the application’s object model The EDM represents a re-useable application model that can be leveraged from within many applications/environments and persisted across numerous databases. The Entity Data Model is RDMS agnostic, and numerous database vendors are currently developing providers: Oracle, DB2, MySQL, PostgreSQL, VistaDB, SQLite, Sybase, Informix, etc. The Entity Data Model primarily of three main concepts: Entities, which represent your domain objects. Associations, which represent a relationship between two entities. Functions, which represent stored procedures or UDFs in your database that can be mapped to model-level functionality. Because there will be plenty of situations where you’ll need to use stored procedures, the Entity Data Model allows you to map functions in your model to a store procedure in your database. This is useful because you can leverage a stored procedure without having to write ADO.NET code to call it, you can simply call a function on your model. EDM functions are represented as methods on your ObjectContext class.
- Estimated Time: 3 minutesTalking Points: This diagram helps to illustrate how each of the Entity Framework’s query options relate to each other. At the core of it all is the database-specific provider. This layer is what translates the query into the SQL flavor required for the underlying data source. Above that is the Entity Client API, which takes the Entity Framework query and passes in down to the database specific provider. If you want to use the Entity Client API directly, you see that you’re only query option is Entity SQL, and because it sits below Object Services, you don’t get any of its benefits. If you want to materialize your queries as objects, and get things like change tracking, identity mapping, relationship loading, etc. then you would use object services, that delegates its queries down to the Entity Client layer. When using Object Services you can leverage both Entity SQL and LINQ to make your queries.
- Estimated Time: 4 minutesTalking Points: The Entity Client is an Entity Framework “port” of the familiar object model of classes used in traditional ADO.NET programming, including:EntityCommandEntityConnectionEntityConnectionStringBuilderEntityDataReaderEntityParameterEntityTransaction Because of this fact it makes it a prime choice for developers migrating to the Entity Framework from ADO.NET. Just like traditional ADO.NET, your queries are returned as sequential text-based data that can iterated over using an EntityDataReader. This is great for performance, but lacks the rich object model that was created as part of your EDM. Entity Client gives you read-only access to your EDM. If data modification is required, you’ll have to use Object Services, which we’ll talk about in a bit. When using Entity Client, your queries are written using Entity SQL, which we’ll talk about in the next slide.
- Estimated Time: 5 minutesTalking Points: While the Entity Client API is great and performant, it lacks the use of our created object model, as well as the ability to update data in our model. The Object Services API sits on top of Entity Client, and provides object materialization on top of our queries. This means that instead of getting text-based results, we get back a collection of CLR objects that we can easily work with. The two mains components of the Object Services taxonomy are: ObjectContext, and ObjectQuery<T>ObjectContext is equivalent to an EntityConnection, and is what manages our connection to the EDM as well as provides crucial services for working with our data.ObjectQuery is equivalent to an EntityCommand and represents a single query executed against our EDM, that is manifested back as strongly-typed objects. Object Services allows you to write queries using two flavors: Entity SQL LINQ To Entities The same Entity SQL queries you would write using Entity Client can be leveraged with Object Services, but with the added benefits you get with the higher abstraction level (i.e. object materialization). While Entity SQL is great for scenarios that require a dynamic query, or greater control over your query’s shape, you’re still working with a string that is error-prone. In addition to Entity SQL, Object Services allows you to write your queries against it in LINQ which provides you with strong-typing, error-checking, and a higher level of abstraction from Entity SQL. If you are already familiar with LINQ, then you don’t have to master Entity SQL in order to query an EDM, because LINQ To Entities will make the translation for you. In addition to object materialization, object services provides you with other benefits/services: Unit of work Your Object Context represents your unit of work, which aggregates all changes made to all entities attached/contained in it, so that when you want to push those changes back to the server, you can do so in a single batch. Identity tracking The ObjectContext keeps track of the entities you’ve queried for by key, so that if you later request the same entity (by key), using the same ObjectContext instance, it will return you the instance it already has instead of re-hitting the database. Eager/explicit loading The Entity Framework doesn’t pre-load any relationship properties for you. If you want to query an entity as well as some of it’s related entities, you’ll need to explicitly request that by performing a “span” using the Include method of the ObjectQuery<T> class. Alternatively you can call the Load method on your entity’s relationship property.
- LINQ has two syntaxesLambda/Method Syntax = customer.Select(...)Comprehension/Query Syntax = from c in customer ...