Don Smith, Program Manager Microsoft patterns & practices

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

5 Keeping Entities Consistent Recommended when domain is less complex Restricts object-oriented design options Can benefit from code generation strategies More difficult to evolve over time, but easier to manage Common patterns Row Data Gateway Table Data Gateway Table Module Active Record Record Set We have choices 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) Contains the data as rows and columns Table Data Gateway Encapsulates all SQL Can return record sets Table Module Accepts a record set Contains business logic TableDataGateway Find() : RecordSet Update(a, b, c) Insert(a, b, c) Delete(id) TableModule Process(RecordSet) Calculate(RecordSet) RecordSet Rows Columns

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

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

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

10 Storefront Reference Implementation

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

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

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

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

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 dons@microsoft.com Project s community site: Patterns of Enterprise Application Architecture The Microsoft Patterns & Practices Team

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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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