ADO.NET 3.0 – Entity Data Model Gert E.R. Drapers Chief Software Architect Visual Studio Team Edition for Database Professionals Microsoft Corporation

Agenda ADO.NET Entity Framework Introduction Application Scenarios –Direct Mapping –Flexible Mapping Scenarios –Extensibility Usage Best Practices Summary

The Entity Framework ADO.NET Providers Dataset ADO.NET 2.0 The Entity Data Model Language Integrated Query (LINQ) ADO.NET Providers Entity Client Dataset Object Services LINQ over Dataset LINQ over Entities ADO.NET Entity Framework

ADO.NET Data Providert ADO.NET Data Provider Entity Framework Overview ADO.NET Data Provider Object Services LINQ to Entities EDM MetaData Store Schema Conceptual Schema Conceptual Schema Object Metadata Object Metadata O-C Map O-C Map C-S Map C-S Map CQT DataReader IEnumerable ESQLNative SQL CQT ESQLLINQ EntityClient Data Provider Client View Engine CQT

EDMGEN.EXE Generates the model files Model.ssdl (Store Schema Definition Language) –Describes tables and columns which map to Entities and Relationships Model.csdl (Conceptual Schema Definition Language) –Describes the Entity Data Model (incl. EntitySets, EntityTypes, Associations & AssociationsSets) Model.msl (Mapping Specification Language) –Describes how the Entity Framework maps between the Conceptual Model (CSDL) and the logical Storage Schema (SSDL) Model.cs or Model.vb –Partial class implementing the model created

Direct Mapping Scenario –Database schema provides appropriate application model Benefits –Relationships –Common Extended Query Language –Common Queryable Schema –Common Metadata Services –Object Services Business Logic Identity Management Change Tracking –Language Integrated Query (LINQ)

Flexible Mapping Scenario –Database schema doesn't match application model Benefits –Richer Application Data Model Inheritance M:N Relationships –Richer Mapping Inheritance options (TPH, TPT, TPC) Stored Procedures Entities split across tables –Decouples application model from storage schema Multiple application models for same store Same application model over different storage schemas Independent evolution of application model/storage schema

Extensibility Scenario: Building a customizable framework Benefits –Flexible run-time mappings i.e., Language-specific mappings –Mapping to "Extensible Schemas" EntityViews –Vertical partitioning of framework and extensions Separate mappings Derived types –Extending data classes

Best Practices Should I use Objects or DataRecords? How long should I hold an ObjectContext? Which mapping techniques should I use? When should I used Stored Procedures or Table Valued Functions? How should I extend data classes? When should I write my own data classes? When should I use Custom Serialization? Should I use LINQ, Query Builder Methods, or eSQL? Should I use LINQ to SQL or LINQ to Entities?

Objects or DataRecords? Objects (IEnumerable ) –Strong typing –Business logic –Updating –Example: Interactive Windows application Data Records (IExtendedDataReader) –Performance for read-only streaming Sequential access Avoid object construction overhead Doesn't require generated classes –Example: Directly serializing results to a Web response

Holding ObjectContext Web scenarios –Typical pattern: Create, Use, dispose –ObjectContext holds resources Connections Object References –Use NoTracking for read-only scenarios Windows Forms scenarios –Hold as long as application interacts with results –ObjectContext mantains state Identity resolution Change tracking –New ObjectContext for each new query Ensures data is fresh

Mapping Techniques Database views –Common access patterns across applications Optimization of access paths through Materialized Views Table/View mappings –Entity properties map directly to database columns Columns have same meaning throughout hierarchy EntitySQL views in MSL –Flexible mappings expressed in EntitySQL Filter based on conditions, read-only properties, non- equality conditions, computed properties, multiple extents mapped to same table Native SQL views in SSDL –Mapping on top of native SQL queries Store-specific queries Expose as "EntitySet" to mapping layer

Stored Procedures and TVFs Stored Procedures –Better control over operations on data within the database Tighter control over operations, permissions Provides level of indirection from storage schema –Use for operations that affect state of the database Inserts, updates, deletes Required for updates against ESQL and Native SQL views –Can return multiple results in one roundtrip Tabled Valued Functions –Better control over access to data within the database Tighter control over operations, permissions Provides level of indirection from storage schema –Use for server-side functions that return data Results of TVF are composable within a query

Extending Data Classes Derivation –Adding new persistent fields to a base class Derived types Customization extensions Partial Classes –Business logic –Methods –Calculated values –Non-persistent fields –Custom serialization "Activity" Classes –Common operations on data classes

Custom Data Classes Entity Framework-generated data classes –Derive from Entity Framework base class Change Tracking, RelationshipManagement Common Notifications, Property Validation Custom data classes –Derive from Entity Framework base class Generate common patterns Insert common intermediate class –Derive from your own base class Implement IEntity/IEntityWithRelationships –Expose EntityKey –Notify ObjectContext when data changes –RelationshipManager property to do relationship fixup Add attributes for persistent fields –How we get O/OC metadata today –Investigating "Persistence Ignorance" scenarios

Custom Serialization Default serialization –Serialize streams of Entities Doesn't navigate relationships in order to avoid cycles Custom serialization –Serialize Graphs Manage relationship serialization to avoid cycles –Serialize to different shapes "Entity Projections"

LINQ, Query Builder, or eSQL? LINQ –Strongly typed queries –Compile-time checking –Embedded in your application –LINQ-Mapped Canonical Functions ObjectQuery builder methods –Queries built from user input –Iterative query building –Store functions eSQL –Dynamic/AdHoc queries –Persistent queries –Store functions

LINQ to SQL or LINQ to Entities? LINQ to SQL –Emphasis on rapid application development –Direct mapping Single type hierarchy to single table/view/stored proc/TVF Simple renaming Derive class for update logic/Stored Procedures –Direct mapping to Microsoft SQL Server family of databases –Microsoft Visual Studio 2008 RTM

LINQ to SQL or LINQ to Entities? LINQ to Entities –Focus on enterprise-grade data scenarios –Flexible Mapping to Relational data Mapping a single class across multiple tables/views Mapping to different types of inheritance Directly modeling Many to Many relationships Mapping to an arbitrary query against the store Common model across products Declarative stored procedures –Access to Microsoft SQL Server family and other databases through ADO.NET provider model –Microsoft Visual Studio 2008 update

The LINQ Project C# 3.0C# 3.0 VB 9.0VB 9.0 OthersOthers.NET Language Integrated Query LINQ to Objects LINQ to DataSets LINQ to SQL LINQ to Entities LINQ to XML Objects XML Relational

Summary Entity Data Model provides an application-oriented data model –Entities and relationships Strong typing, polymorphism Client Views provide flexible mapping to your storage schema –Entities split between tables, Many:Many relationships, mapping to store queries, etc. Entity Framework lets you opt-in according to your requirements –DataReaders/Objects –eSQL/QueryBuilder/LINQ –Generated/Custom Data Classes

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