Introducing the Entity Framework

Introducing the Entity
Framework

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Objectives


Objectives
• Learn about how object-relational mapping
works to provide data access


Objectives
• Understand what the Entity Framework is and
how it can provide robust data access services to
applications


Objectives
applications
• See how to build a database-first Entity Data
Model using Visual Studio


Objectives
applications
• See how to build a database-first Entity Data
Model using Visual Studio
• Explore the various Entity Framework APIs and
tools


Agenda


Agenda
• Object-Relational Mapping (ORM) and
Data Access


Agenda
Data Access
• The Entity Framework and Data Model


Agenda
Data Access
• Building a Simple Application using Entity
Framework


Agenda
Data Access
Framework
• Entity Framework APIs and Tools


Object-Relational Mapping (ORM)


• Just about all applications make use of data


• Microsoft has a long history of providing data access
technologies


technologies
• But they have problems


technologies
 Too close to the metal


technologies
 Use generic data objects


technologies
• Data access code is usually a lot of code


technologies
• Differences between objects and database


technologies
• Entity Framework bridges the gap


technologies
• Entity Framework bridges the gap
• Terminology: data store and database

Object/Relational Differences


• Inherent problems application has to overcome


 Needs lots of code somewhere


 Big impact on application design, effort, and
performance


 Big impact on application design, effort, and
performance
• Will discuss in the context of a relational
database


Data Type Differences


• Many kinds of data types


• SQL Server 2008 R2 data types:


bigint binary bit char CLR
date datetime datetime2 datetimeoffset decimal
float hierarchyid image int money
nchar ntext numeric nvarchar real
rowversion smalldatetime smallint smallmoney sql_variant
table text time timestamp tinyint
varbinary varchar uniqueidentifier


bigint binary bit char CLR
date datetime datetime2 datetimeoffset decimal
float hierarchyid image int money
nchar ntext numeric nvarchar real
rowversion smalldatetime smallint smallmoney sql_variant
table text time timestamp tinyint
varbinary varchar uniqueidentifier
• Some have direct equivalents in .NET
• Database types often have constraints
• Binary data in the database can be anything
• Dates and times are another issue

Relationship Difference


• Databases use foreign key constraints


• .NET objects use object references


• .NET objects use object references
• SalesOrderHeader and SalesOrderDetail tables


• Many-to-Many relationships


• In AdventureWorks, customers and addresses


• In AdventureWorks, customers and addresses

• Not the default objects

Inheritance Difference


• .NET supports object inheritance


 No support for multiple inheritance


• Inheritance makes code simpler, maintainable, easier
to debug


to debug
 Model hierarchies of objects


to debug
• Relational databases don’t support inheritance


to debug
• Some ways to accomplish it


to debug
 Table per type


to debug
 Table per type
 Table per concrete type


to debug
 Table per type
 Table per hierarchy


to debug
 Table per type
 Table per hierarchy
• Have to manage special constraints

Identity/Equality Difference


• How do you tell two things are the same?


• Database: identity of a row is the primary key


 Enforced by a primary key constraint


 Can use either natural or surrogate keys


• Objects in object-oriented application


 Two objects with the same data are not equal


 Two variables, each with reference to different
objects, are not equal


 Two variables with reference to same object are equal


 Two variables with reference to same object are equal
 Can make a custom definition


Handling the Differences


• Can be an lot of work to handle object/relational
differences


differences
 But at least they are well understood


differences
 Doesn’t mean it’s easy


differences
 Doesn’t mean it’s easy
• Write the code yourself, or use a framework


• Programming technique for conversion of
incompatible types


incompatible types
• Most ORM tools rely on metadata about
database and objects


incompatible types
• Clean separation of concerns


incompatible types
• Key feature is mapping


incompatible types
 Expresses how an object is related to a table


incompatible types
 ORM uses to manage conversion process


incompatible types
 ORM uses to manage conversion process
• ORM manages application’s interactions with
database

Benefits to using an ORM


• Productivity


• Productivity
• Better application design


• Productivity
• Code reuse


• Productivity
• Code reuse
• Application maintainability


• Productivity
• Code reuse
• Potential downside: performance


• Productivity
• Code reuse
 More complex code


• Productivity
• Code reuse
 Means slower performance


• Productivity
• Code reuse
 But ORM code is likely to be well tuned


• Productivity
• Code reuse
 Data access time may be minimal


• Productivity
• Code reuse
 Data access time may be minimal
• Lots of ORMs available for .NET

Generic Data Objects vs. Entity


• ADO.NET has long had generic data objects


• Most common:


• Most common:
 SqlConnection and OleDbConnection


• Most common:
 SqlDataAdapter and OleDbAdapter


• Most common:
 DataSet


• Most common:
 DataSet
 DataTable


• Most common:
 DataSet
 DataTable
 SqlDataReader and OleDbDataReader


• Most common:
 DataSet
 DataTable
• Provide a means for accessing data in database


• Most common:
 DataSet
 DataTable
• Provide a means for accessing data in database
 DataSet and DataTable contain rows and columns


Generic Data Objects


• Problems with Generic Data Objects


 Strong coupling between application and database


 Loose typing


 Loose typing
 Object interactions


 Loose typing
• Problems persist despite long use


 Loose typing
 Every application has to deal with them


 Loose typing
 Every application has to deal with them
 But it’s been the best we’ve had, other than custom
objects


Entity Data Objects


Entity Data Objects
• Big improvement over what came before


Entity Data Objects
 Instead of using a generic DataSet, use Customer,
Order, and OrderDetail


Entity Data Objects
 Navigation properties to access related data


Entity Data Objects
 Fit into object-oriented application


Entity Data Objects
• Object interfaces can mirror tables and fields


Entity Data Objects
 Or be completely different


Entity Data Objects
 Or something in between


Entity Data Objects
 Or something in between
• Need a way to map objects to database


Benefits of Entity Data Objects


• Strong typing


• Strong typing
• Compile-time checking


• Strong typing
• Persistence ignorance


• Strong typing
• Persistence ignorance
• Productivity


Data Programming Against a Model


• Will have to change how you think about data in
an application


an application
 No longer interacting directly with the database


an application
 Instead working with objects


an application
 Very different paradigms


an application
• The model is not the database!


an application
• Generic data objects require lots of code


an application
• Entity data objects mean querying a schema that
reflects business model


an application
• Entity data objects mean querying a schema that
reflects business model
• ORM eliminates context shift in code

Agenda
• Object-Relational Mapping (ORM) and Data
Access


Agenda
Access


Agenda
Access
Framework


Agenda
Access
Framework
• Entity Framework APIs and Tools


The Entity Framework and Data
Model


Model
• Complete ORM for .NET applications


Model
• Microsoft’s new core data access technology


Model
 Big commitment from the company


Model
• Initial release didn’t gain much traction


Model
• Version 4.1 is a mature product


Model
 Substantial commitment and innovation


Model
• Do we need a new data access technology?


Model
 Older technologies have run their course


Model
 Modern applications have to focus on domain model


Model
 Modern applications have to focus on domain model
• Version numbers

Entity Data Model


Entity Data Model
• Integral part of Entity Framework


Entity Data Model
• Client-side model different from database schema


Entity Data Model
• Describes structure of entity data objects


Entity Data Model
• Take the database schema and reshape it into
objects


Entity Data Model
objects
• Defined by three chunks of XML in a single .edmx
file


Entity Data Model
objects
file
 Conceptual model


Entity Data Model
objects
file
 Storage model


Entity Data Model
objects
file
 Storage model
 Mapping


LINQ to SQL


LINQ to SQL
• Similar to Entity Framework


LINQ to SQL
 Both use LINQ to query a database using a data
model


LINQ to SQL
model
• Developed independently at Microsoft


LINQ to SQL
model
 LINQ to SQL grew out of LINQ team


LINQ to SQL
model
 Entity Framework grew out of Data Programmability
team


LINQ to SQL
model
team
• Soon Microsoft had two new data access
technologies


LINQ to SQL
model
team
• Soon Microsoft had two new data access
technologies
• LINQ to SQL moved, and lost out to Entity
Framework

Why Use Entity Framework?


• Part of the .NET Framework and integrated into
Visual Studio


Visual Studio
• Uses LINQ as the primary query language


Visual Studio
• Independent of the data source


Visual Studio
• Independent of the data source
• Microsoft’s primary data access strategy


When Should You Not Use Entity
Framework or an ORM?


• Entity Framework is not a panacea


 Not an instant data access panacea


 Isn’t appropriate for every kind of application


 Isn’t appropriate for every kind of application
 Doesn’t do bulk inserts


Building a Simple Application using
Entity Framework


Entity Framework
• Compelling reason to use Entity Framework is its
integration with Visual Studio


Entity Framework
• Sample is based on AdventureWorksLT


Entity Framework
 Ten tables with data about customers, products, and
orders


Entity Framework
orders
 Complex enough to exercise Entity Framework


Entity Framework
orders
• Will build sample as a class library


Entity Framework
orders
 Easy to reuse in multiple applications


Entity Framework
orders
 Not absolutely necessary


Entity Framework
orders
 Not absolutely necessary
• Mostly create simple console applications

Using the Entity Objects


• Time to use the entity data objects in an
application


application
• Simple console application


application
• Need to do three things to use the class library


application
 Add a reference to the class library


application
 Add a reference to System.Data.Entity


application
 Add the Entity Framework connection string


application
 Add the Entity Framework connection string
• And, of course, write some code!


Entity Framework APIs and Tools


• Entity Framework is a complex set of APIs and
design tools


design tools
• Need a basic understanding of what each of the
Entity Framework components do


design tools
• Need a basic understanding of what each of the
Entity Framework components do
 Road to deep understanding


Architecture


Application
Architecture


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query

Object Services


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results

Object Services


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results

Object Services

Command
Tree


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results

Object Services

Command
Tree

EntityClient Data Provider


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results

Object Services

Command
Entity
Tree
Data
Reader



Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results
Entity
SQL
Query Object Services

Command
Entity
Tree
Data
Reader



Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results
Entity
SQL

Command
Entity
Tree
Data
Reader


Command
Tree


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results
Entity
SQL

Command
Entity
Tree
Data
Reader


Command
Tree

ADO.NET Data Providers


Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results
Entity
SQL

Command
Entity
Tree
Data
Reader


Command
Tree DB Data
Reader



Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Results
Entity
SQL

Command
Entity
Tree
Data
Reader


Command
Tree DB Data
Reader


Data Store

Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Entity Data Results
Entity
Model SQL

Command
Entity
Tree
Data
Reader


Command
Tree DB Data
Reader


Data Store

Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Entity Data Results
Entity
Model SQL
Conceptual
Model Command
Entity
Tree
Data
Reader


Command
Tree DB Data
Reader


Data Store

Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Entity Data Results
Entity
Model SQL
Conceptual
Model Command
Entity
Tree
Data
Reader


Command
Tree DB Data
Storage Reader
Model

Data Store

Application
Architecture Entity
SQL
LINQ to
Entities
Query Query
Entity Data Results
Entity
Model SQL
Conceptual
Model Command
Entity
Tree
Data
Reader
Mapping


Command
Tree DB Data
Storage Reader
Model

Data Store

Entity Data Model Designer


• Part of Visual Studio


• Lets you work with model graphically rather than
as raw XML


as raw XML
• First saw as part of the AdventureWorksLibrary
project


as raw XML
project
• Doesn’t support all Entity Data Model features


as raw XML
project
• Lets you map tables, views, stored procedures
and functions to entities


as raw XML
project
• Lets you map tables, views, stored procedures
and functions to entities
 Can update the model from the underlying database


Design Methodologies Using the
Designer


Designer
• Two broad ways to build a data application


Designer
 Top-down design


Designer
 Top-down design
 Bottom-up design


Designer
 Top-down design
• Neither is necessarily better than the other


Designer
 Top-down design
• Entity Framework supports both


Designer
 Top-down design
• Provides three ways to build an application


Designer
 Top-down design
 Database-first design


Designer
 Top-down design
 Model-first design


Designer
 Top-down design
 Model-first design
 Code-first design


Code Generation Using T4


• Entity Data Model designer generates code


• Uses Visual Studio’s Text Template
Transformation Toolkit (T4)


• Uses Visual Studio’s Text Template
Transformation Toolkit (T4)
 Generates classes in designer code file


Introducing the Entity Framework

Introducing the Entity Framework

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