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Modern Data Access: Patterns & Implementations
Don Smith, Program ManagerMicrosoft patterns & practices
Agenda
The data access layer and your optionsPatterns for keeping entities consistentPatterns for managing entity differencesData access technology assessmentOther data access challengesSummary and questions
Layers & Relationships
ConsiderationsDomain complexityDeveloper experienceGreenfield vs. brownfieldDesired approach: data, code, or model first?Object/schema fidelity
Two OptionsKeep entities consistentManage their differences
Data Access Layer DataStorage
BusinessLogic Layer
BusinessLogicLayer
Data Storage
Keeping Entities Consistent
Recommended when domain is less complexRestricts object-oriented design optionsCan benefit from code generation strategiesMore difficult to evolve over time, but easier to manage
Common patternsRow Data GatewayTable Data GatewayTable ModuleActive RecordRecord Set
We have choicesShape of the objectsHow to combinedata and logic
Pre-Built Types
Record Set (DataSet)Contains the data as rows and columns
Table Data GatewayEncapsulates all SQLCan return record sets
Table ModuleAccepts a record setContains business logic
when objects and schema have a simple relationship
RowsColumns
RecordSet
Find() : RecordSetUpdate(a, b, c)Insert(a, b, c)Delete(id)
TableDataGateway
Process(RecordSet)Calculate(RecordSet)
TableModule
Custom Types
Row Data GatewayRepresents a table’s rowIncludes all CRUD capability
Transaction ScriptContains business logic
Active RecordRepresents a table’s rowContains business logicIncludes all CRUD capability
ID : longFirstName : stringLastName : stringUpdate(first, last)Insert(first, last)Delete(id)
RowDataGateway
ID : longFirstName : stringLastName : stringUpdate(first, last)Insert(first, last)Delete(id)Process()
ActiveRecord
ProcessCostChange()CalculateAdjustment()
TransactionScript
when objects and schema have a simple relationship
Managing Entity Differences
Appropriate for complex domain logicRequires more developer experienceCan leverage more OO (GoF) design patternsAppropriate for apps that evolve over time
Common patternsDomain ModelData MapperRepositoryUnit of WorkSpecification
Storefront Overview
SQLServer
ASP.NETMVC
DataServices
Customer Retailer
Broker
• Manages product information• Maintains
inventory• Processes and
ships orders
IE WPF
Silverlight
• Collects a percentage from each sale• Views sales & site usage reports
• Searches for products• Buys products• Views order
status• Rates products
and retailers
Domain Model & Mapping
Domain ModelAn object model that represents the domainContains the combination of data and business logicTwo basic options
May be robust and leverage OO principlesMay be straightforward in less complex scenarios
May have no knowledge of data access technology
Data MapperRepresents an association of types and properties across the domain model and data modelAlmost always aware of the data access technologyImplementations are often included in O/RM solutionsMapping support varies
Repository
Collection-type interface to data accessMediates between domain model and mapperImplementations are specific to a technology
GetById(id)GetAll()Add(object)Update(object)Delete(id)
Repository
Unit of Work
Maintains a list of new, changed and deleted objects and coordinates persisting changesCan be used across multiple repositories
SubmitChanges()CancelChanges()
UnitOfWork
Specification/Query Object
An object that represents the criteria of a query Allows queries to be easier to manageAvoids the need for a method for each query
Field : stringValue : objectOperator : OpEnum
Specification
Technology Assessment
ADO.NETDataSetDataAdapterDataReader
LINQ to SQLO/RM for simple mappings
ADO.NET Entity FrameworkO/RM for more complex mappings
Related Challenges
Domain Model ResponsibilitiesSerialization (DTOs)Data bindingEdit trackingValidation
Domain Model RepresentationsSubset of the typeView models
Summary
Steps for making choices1. Determine consistency possibilities between the
domain model and the data modelKeep entities consistentManage their differences
2. Choose shape of the typesPre-builtCustom built
3. Determine how to attach the business logicInfluenced by the shape of the types
Resources
Don’s email: [email protected]’s community site: http://dataguidance.codeplex.comPatterns of Enterprise Application Architecturehttp://www.martinfowler.com/eaaCatalogThe Microsoft Patterns & Practices Teamhttp://microsoft.com/practices
© 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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