intro to entity framework

Intro to Entity Framework

A Reconnaissance(No Driving Yet)

Tom Perkins

Objectives

• Last Session: – We created a small Entity Framework application step-

by-step and – displayed data in a GridView from a database.

• This Session: – We’ll again create a small Entity Framework application.– We’ll look at the components in more detail for the

purpose of gaining familiarity with what the Framework produces.

• Work along or watch!

A Different Programming Perspective

ApplicationEntity Data

Model(EDM)

Data Store

Developer

bridge

Focus on business objectsFocus on tables, stored Procedures, views, etc.

EDM is a “concept”Entity Data Model

(EDM)

Implemented as:

EDMX File

Design timeRun time

3 XML Files

XML Files

Entire Model

Entity Data Model Schema

Mappings

Database Objects Schema

*.CSDL

*.MSL

*.SSDL

*.EDMX

Design Time Run Time

Compile

What Entity Framework Does

• Generates classes from model• Updates classes as model changes• Handles database connectivity• Querying done on model, not database• Translates queries into database queries• Tracks changes to objects in the model• Handles updates to the database

Build a simple EDM

• Sample database, ProgrammingEFDB1• 2 tables, one view, some stored procedures• Create a new Console Application

In VS2010, File | New | ProjectSelect Console Application

Name: Chapter2ConsoleAppLocation: (use default)Solution: ProgrammingEntityFramework

Click OK

•Right-click on Chapter2ConsoleApp in the Solution Explorer•Add | New Item

Select ADO.NET Entity Data Model from the Templates list | Add

Select Generate from database | Next

Make sure your local SQL Server is activeSet up a new connection if necessaryChange the App.Config settings name to “Sample Entities” | Next

Select Tables, Views | Change Model Namespace to SampleModel | Finish

New model appears. Note Model1.edmx file. To display the model at any time, double-click on the Model1.edmx file in the Solution Explorer.

THE DESIGNER WINDOW

Gives a graphical view of the EDM and its members. Contact Entity, Address Entity, and vOfficeAddressEntity 2 from DB Tables, one from View connecting line One-to-Many relationship associations Scalar properties (ContactID, FirstName, etc) Navigation properties (Addresses, Contact) – Addresses property enables navigation from Contact Entity to set of Addresses related to that contact

Using the Properties Window• A logical group of entities entity container• Click in the white space of the Designer Window, then look at

the Properties window.

You can modify the Entity Container Name and the Namespace You can set whether to pluralize new objects or not

The Properties of an Entity• Click on the Contact Entity

Entity name: Contact db table Entity Set Name pluralized Entity names should be singular

Entity set a container for entities of a single type

The Properties of an Entity Property

• Click on Contact’s FirstName property

FirstName is a non-nullable string with a maximum length of 50 characters, variable. It is not the Entity key.

The framework does not perform validation of the Max Length, Unicode, and Fixed Length properties. These properties are ignored.

THE RAW FORMAT OF THE MODEL-- XML –

SUPPORTING METADATA

XML Files

Entire Model

Entity Data Model Schema

Mappings

Database Objects Schema

*.CSDL

*.MSL

*.SSDL

*.EDMX

Design Time Run Time

Compile

Supporting Metadata

• Sections– ConceptualModels– StorageModels (db schema)– Mappings

• Last 2 tell how to translate between conceptual model and actual data store

• Mapping – translates entities and properties (conceptual model) to tables and columns (StorageModel)

• Physical files stored in project assembly at compile time (you won’t see them).

The Model Browser

• Right-click on the design surface• Choose Model Browser from the context menu.• Gives another view of the metadata.

Raw XML

• Only a portion of the model is visible in the Designer.• View complete model in XML form.• To see the raw format of the model:

– In Solution Explorer– Right-click on Model1.edmx file– On context menu

• Select “Open With”• Choose XML Editor• Click OK• (Only one view of the model at a time is allowed – click OK to

close the Design View of the model when prompted.)

Raw XML in the Designer

Model with Sections Collapsed• To collapse the model

– Right-click on XML– Choose Outlining– Toggle All Outlining– Expand nodes to get the main sections of the model:

CSDL: The Conceptual Schema

• If a line loses its hard returns, – Highlight the line– From VS Menu, select Edit | Advanced | Format

Selection to format the line• In ConceptualModels section, Click on + icons

to expose the Schema and EntityContainer

Expanded Schema and Entity Container nodes

The above XML is the source of the graphical display we saw in the Designer.

Model Elements We’ll Examine

• Entity Container• Entity Set• Entity Type• The Key Element• Property Elements• Associations• Navigation Property

The Entity Container

• Name: – Defaults from model name– Change in model’s Property Window

• Wrapper for Entity Sets and Association Sets• Exposes Entity Sets– You write queries against these

The Entity ContainerQUERY

Entity Container

ContactsAddresses

Contact Object

Contact Object

Contact Object

Address Object

Address Object

LazyLoading Annotation used as directions for generation of code

The Entity Set• Gives access to individual entities when querying against

model• Example: “find some entities in the Contact EntitySet”

returns some Contact Entity Types• Entity Type: Strongly Typed Name for Entity

<EntitySet Name="Addresses" EntityType="SampleModel.Address" /> <EntitySet Name="Contacts" EntityType="SampleModel.Contact" /> <EntitySet Name="vOfficeAddresses" EntityType="SampleModel.vOfficeAddress" />

The Entity Type• <EntityType Name="Address">• <Key>• <PropertyRef Name="addressID" />• </Key>• <Property Name="addressID" Type="Int32" Nullable="false" annotation:StoreGeneratedPattern="Identity" />• <Property Name="Street1" Type="String" MaxLength="50" Unicode="true" FixedLength="false" />• <Property Name="Street2" Type="String" MaxLength="50" Unicode="true" FixedLength="false" />• <Property Name="City" Type="String" MaxLength="50" Unicode="true" FixedLength="false" />• <Property Name="StateProvince" Type="String" MaxLength="50" Unicode="true" FixedLength="false" />• <Property Name="CountryRegion" Type="String" MaxLength="50" Unicode="true" FixedLength="false" />• <Property Name="PostalCode" Type="String" MaxLength="50" Unicode="true" FixedLength="false" />• <Property Name="AddressType" Type="String" Nullable="false" MaxLength="50" Unicode="true"

FixedLength="false" />• <Property Name="ContactID" Type="Int32" Nullable="false" />• <Property Name="ModifiedDate" Type="DateTime" Nullable="false" />• <NavigationProperty Name="Contact" Relationship="SampleModel.FK_Address_Contact" FromRole="Address"

ToRole="Contact" />• </EntityType>

Key element: Identity key for entity; may be compositetracks entity, helps perform updates and refreshes, very important

Property Elements

• Can’t have XML and Designer open at the same time

• Close XML view, double-click .edmx file to view an element’s properties

• Not all propertes appear in XML , but do appear in Properties window– Currency mode, default value, Getter, Setter

• “Facets” are used to describe properties

Association• Defines relationships

between entity types• Describes “end points” of

relationship and multiplicity (1, 0..1,*)

• Cascade – if Contact is deleted, delete associated Addresses

• Let’s look at the view in the Designer … Close the XML and double-click on the Model1.edmx in the Solution Explorer.

<Association Name="FK_Address_Contact"> <End Role="Contact" Type="SampleModel.Contact" Multiplicity="1"> <OnDelete Action="Cascade" /> </End> <End Role="Address" Type="SampleModel.Address"

Multiplicity="*" /> <ReferentialConstraint> <Principal Role="Contact"> <PropertyRef Name="ContactID" /> </Principal> <Dependent Role="Address"> <PropertyRef Name="ContactID" /> </Dependent> </ReferentialConstraint>

FK_Address_Contact Association• Defines relationships between

entities – Contact and Address• Focuses on “endpoints”• End1

– Contact– Assigned “role” – Contact– Also name that can be used in model to

point to this end– Multiplicity (only one Contact)– Navigation – other end of association– Cascade – delete addresses if contact is

deleted

• End2– Role – Address– Multiplicity – many addresses per contact– Association Set – may be more than one

per entity

Referential Constraint

• For Foreign Keys• Shows dependency between related entities• Every Address must have a Contact• Used to maintain integrity of database

Address_Contact Navigation Property

• Shows how to navigate to associated entity

• Association – how to navigate to associated entity (or entities)

• From Role, To Role – navigate from Address to Contact

• Multiplicity – returns 1 Contact object

Contact.Addresses Navigation• This Navigation Property returns a

collection of addresses• No address for Contact, collection

will be empty• “Type” is a special EntityCollection,

not type implementing System.Collections.ICollection (not interchangeable)

This CDSL

• Simple model• Conceptual Layer mirrors the database

schema• Customizing the model (later) gives real power

to Entity Framework

SSDL (STORAGEMODEL SECTION)

Expanded StorageModels Section

StorageModels Section• Provides a description of the data store (database)• Tables called Type, Columns called Property• “Store” is in Namespace to minimize confusion• ProviderManifestToken – version of SQL Server

– You must modify manually if switching to SQL Server 2005• Entity container – derived from db name• Entity Type – name of table

– Property types – SQL Server data types– Identity column – StoreGeneratedPattern=“Identity” – identity value generated

by db when row is inserted, will not change– Other options

• “Computed” – values generated• “None” - default

MSL: MAPPING FROM CONCEPTUAL MODEL TO STORAGE (AND BACK)

MSL: Mappings Section

• Logically between concept and storage models• Maps entity properties back to tables and

columns of data store• Enables further customization of model• Use the Mapping Details Window– (Close XML view) Open Designer (dbl-clk on .edmx)– Right Click on Contact Entity– Select Table Mapping

Mapping Details Window

• Maps Contact entity to Contact table• Maps to Contact Contact table in SSDL• Here, one to one relationship – can be customized• When you create mappings, wizard matches names for you• Note SQL data types

Database Views: vOfficeAddress

• Note: DefiningQuery

Summary

• Introduced you to EDM and design tools• Created an EDM• Looked under the hood• Raw XML• Mappings• Enough to get started with Querying• Stay tuned for more exciting developments