Introduction to ADO'NET ObjectSpaces

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Introduction to ADO.NET ObjectSpaces Alex
ThissenTwice IT Training
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Agenda

• What is ADO.NET ObjectSpaces?
• ObjectSpaces architecture
• Mappings
• Common classes
• OPath query language
• Questions and Answers

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What is ObjectSpaces?

• Object-Relational framework
• Abstraction layer between
• objects from application logic
• data source
• Extra layer on top of ADO.NET
• Non-intrusive for object model
• Dynamically builds SQL statements based on XML
  definitions of objects and database

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Overview ObjectSpaces architecture
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Three mapping files

• Object Schema Document (.osd)
• Defines business objects and members
• Specifies relations between types of objects
• Relational Schema Document (.rsd)
• Defines tables and views
• Mapping Schema Document (.msd)
• Combines OSD and RSD
• Maps between objects and tables
• Also specifies how object-relations map to
  table-relationships

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Types of relationships

• Object relationships
• One to One, One to Many, Many to Many
• Inheritance
• Objects to Table mappings
• One object stored in one or more tables
• Multiple objects stored in one table

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DEMO

• Business objects
• Object Mapper Utility

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ObjectSet

• In-memory set of objects from source
• Resembles DataSet
• Keeps original values for optimistic concurrency
• Can be bound to data controls
• Streamable as XML (DiffGram style)
• Automatic tracking of objects

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ObjectReader

• Provides a stream of objects from source
• Enumerate using foreach loop or while loop
• Is forward-only (not read-only)

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ObjectSpace class

• Handles communication to and from data source
• Supports
• State management
• Transactions
• Needs
• One or more DB connections (ObjectSources)
• Mapping file (MappingSchema)
• Retrieve objects using
• GetObject, GetObjectSet, GetObjectReader

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ObjectQuery

• Query that specifies search criteria for
  retrieving objects
• GetObject, GetObjectReader, GetObjectSet
• Needs three parameters
• Type of object to retrieve
• OPath query expression
• Span (depth) of object hierarchy to return

ObjectQuery oq new ObjectQuery(typeof(Posting),
"ltOPath expressiongt", "ltSpangt") ObjectReader
or ObjectSpace.GetObjectReader(oq)
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ObjectContext

• Implicitly used by ObjectSpace and ObjectSet
• Manages object identity
• When object is requested that has been returned
  before, same object reference is used
• Also works for links between objects
• Weak references are used
• More advanced scenarios work with ObjectContext
  explicitly

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OPath Query language

• OPath expressions are used to retrieve subsets of
  objects from source
• Similar to XPath expressions
• Filtering using predicates
• Navigate object relations with dot (.) notation

// Some examples OrdersFreight gt
5.Details.Quantity gt 50 Customer.AddressState
Like 'A-C' Customer.Country 'USA' AND
Customer.Region 'WA' AddressState In ('WA',
'OR', 'ID') IIF(Gender 'M', 67, 72) - Age lt
Term Id Like ? AND OrdersFreight gt ?
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DEMO

• Retrieving objects
• ObjectSet
• Creating and storing objects

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Advanced features

• Delayed loading of nested objects
• Collections are kept inside ObjectList instead of
  classes like ArrayList
• "Read-only" objects
• Not tracked by an ObjectContext
• Optimal performance
• Compiled queries

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Things to keep in mind

• "This" release only supports SQL Server 2000 or
  later as datasource
• Although data source should implement
  IDbConnection
• Cannot run (yet) from "in-process" Yukon stored
  procedures
• Performance will be similar to working with
  DataAdapters and DataSets

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Resources and links

• PDC 2003 Samples
• ObjectSpaces Mapper Utility
• Object Persistence Sample
• System.Data.ObjectSpaces documentation
• Mail to osfdbk_at_microsoft.com

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Questions and Answers

• ?