The document provides an agenda and overview for a presentation on data access layer patterns and options. It discusses considerations for keeping data entities consistent or managing differences between objects and schemas. It also covers common patterns for each approach, including row and table data gateways, active record, domain models, data mappers, repositories, and unit of work. The presentation will assess data access technologies and discuss additional challenges like domain model responsibilities. Attendees can contact the presenter with any other questions.

2. Don Smith, Program Manager
Microsoft patterns & practices

3. Agenda
The data access layer and your options
Patterns for keeping entities consistent
Patterns for managing entity differences
Data access technology assessment
Other data access challenges
Summary and questions

4. Layers & Relationships
Business
Business Data
Data
Logic Data Access Layer
Logic Storage
Storage
Layer
Layer
Considerations Two Options
Domain complexity Keep
Developer experience entities
Greenfield vs. brownfield consistent
Desired approach: data, Manage their
code, or model first? differences
Object/schema fidelity

5. Keeping Entities Consistent
Recommended when Common patterns
domain is less complex Row Data Gateway
Restricts object-oriented Table Data Gateway
design options Table Module
Can benefit from code Active Record
generation strategies Record Set
More difficult to evolve
over time, but easier to We have choices
manage Shape of the objects
How to combine
data and logic

6. Pre-Built Types
when objects and schema have a simple relationship
Record Set (DataSet) TableDataGateway
Contains the data as rows Find() : RecordSet
and columns Update(a, b, c)
Insert(a, b, c)
Table Data Gateway Delete(id) RecordSet
Encapsulates all SQL Rows
Can return record sets Columns
Table Module
TableModule
Accepts a record set
Process(RecordSet)
Contains business logic Calculate(RecordSet)

7. Custom Types
when objects and schema have a simple relationship
Row Data Gateway RowDataGateway
Represents a table’s row ID : long ActiveRecord
Includes all CRUD FirstName : string
ID : long
capability LastName : string
FirstName : string
Update(first, last)
Transaction Script Insert(first, last)
LastName : string
Update(first, last)
Contains business logic Delete(id)
Insert(first, last)
Active Record Delete(id)
Represents a table’s row Process()
Contains business logic TransactionScript
Includes all CRUD
ProcessCostChange()
capability CalculateAdjustment()

8. Managing Entity Differences
Appropriate for Common patterns
complex domain logic Domain Model
Requires more Data Mapper
developer experience Repository
Can leverage more OO Unit of Work
(GoF) design patterns Specification
Appropriate for apps
that evolve over time

9. Storefront Overview
Customer Retailer
IE WPF
ASP.NET Data
MVC Services
• Searches for • Manages product
products information
• Buys products • Maintains
• Views order SQL inventory
Server
status • Processes and
• Rates products ships orders
and retailers Broker
• Collects a percentage from each sale
• Views sales & site usage reports
Silverlight

10. Storefront Reference Implementation

11. Domain Model & Mapping
Domain Model Data Mapper
An object model that Represents an association of
represents the domain types and properties across the
Contains the combination of domain model and data model
data and business logic Almost always aware of the
Two basic options data access technology
May be robust and leverage OO Implementations are often
principles included in O/RM solutions
May be straightforward in less Mapping support varies
complex scenarios
May have no knowledge of data
access technology

12. Repository
Collection-type interface
to data access
Repository
Mediates between GetById(id)
domain model GetAll()
Add(object)
and mapper Update(object)
Delete(id)
Implementations are
specific to a technology

13. Unit of Work
Maintains a list of new,
changed and deleted
UnitOfWork
objects and coordinates SubmitChanges()
persisting changes CancelChanges()
Can be used across
multiple repositories

14. Specification/Query Object
An object that represents
the criteria of a query
Allows queries to be Specification
easier to manage Field : string
Value : object
Avoids the need for a Operator : OpEnum
method for each query

15. Technology Assessment
ADO.NET
DataSet
DataAdapter
DataReader
LINQ to SQL
O/RM for simple mappings
ADO.NET Entity Framework
O/RM for more complex mappings

16. Related Challenges
Domain Model Responsibilities
Serialization (DTOs)
Data binding
Edit tracking
Validation
Domain Model Representations
Subset of the type
View models

17. Summary
Steps for making choices
1. Determine consistency possibilities between the
domain model and the data model
Keep entities consistent
Manage their differences
2. Choose shape of the types
Pre-built
Custom built
3. Determine how to attach the business logic
Influenced by the shape of the types

18. Resources
Don’s email:
dons@microsoft.com
Project’s community site:
http://dataguidance.codeplex.com
Patterns of Enterprise Application Architecture
http://www.martinfowler.com/eaaCatalog
The Microsoft Patterns & Practices Team
http://microsoft.com/practices

20. © 2009 Microsoft Corporation. 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.

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