Entity Framework - Object Services

EF Object Services
Eyal Vardi
CEO E4D Solutions LTDMicrosoft MVP Visual C#blog: www.eVardi.com

Agenda
EF Architecture
Development Approaches
Entity Data Model (EDM)
Object Services
Querying & Loading Entities
EDM
LINQ to Entities
Entity SQL
Conceptual Model
Object Services
Mapping
Entity Client Provider
StorageModel
ADO.NET Provider

Services:- Change tracking- Concurrency control- Object identity
SQL or Stored Procs
Rows
SQLServer
Entity Framework
EF Architecture
Application
from c in db.Customerswhere c.City == "London"select new { c.Name, c.Phone }
Objects
LINQ Query
SubmitChanges()
EDMX
ADO.NET Provider
SQL Query
select Name, Phonefrom customerswhere city = 'London'

EF Architecture
SQLServer
EDM
LINQ to Entities
Entity SQL
Conceptual Model
Object Services
Mapping
Entity Client Provider
StorageModel
ADO.NET Provider

Object Services
Materialization
The process of transforming the data obtained from the Entity Client data provider, which has a tabular structure, into objects.
Change tracking
Tracks any changes made to the objects.
Query transformation
Translates queries it into a command tree that’s then passed on to the underlying Entity Client.
Object identities

Object Services Functions
Querying
Querying data as objects
Shaping query results
Composing queries
CRUD
Lazy loading
Inheritance
Navigating relationship
Change tracking
Saving changes
Attaching objects
Detaching objects
Serializing objects
Managing
Object identities
Concurrency
Transactions

LINQ to Entities (Finding)
DbSet and IDbSet implement IQueryable.
DbSetand IDbSet always create queries against the database
always involve a round trip to the database even if the entities returned already exist in the context.

Finding an Entity by Primary Key
Look on the context
A round-trip to the database will only be made if the entity with the given key is not found in the context.

Eagerly Loading
Eager loading is the process whereby a query for one type of entity also loads related entities as part of the query.

Eagerly Loading (multiple levels)
It is also possible to eagerly load multiple levels of related entities.

Lazy Loading
POCO Properties Must be Virtual.
Configuration.LazyLoadingEnabled = true;

Explicitly Loading
Even with lazy loading disabled it is still possible to lazily load related entities, but it must be done with an explicit call.

Explicitly Loading

Count Related Entities Without Loading Them

Local Data
The Local property of DbSetprovides simple access to the entities of the set that are currently being tracked by the context and have not been marked as Deleted.
Accessing the Local property never causes a query to be sent to the database.

No Tracking Queries
Sometimes you may want to get entities back from a query but not have those entities be tracked by the context.
Better performance
Read-only scenarios

Entity States & Save Changes
Entity states before & After Save Changes.

Adding a New Entity to the Context

Adding a New Entity to the Context
Add a new entity to the context by hooking it up to another entity that is already being tracked.

Attaching an Existing Entity to the Context
Entity that already exists in the database but which is not currently being tracked by the context then you can tell the context to track the entity using the Attach method on DbSet.

Original & Current Values

Marking a Property as Modified
Marking a property as modified forces an update to be send to the database for the property when SaveChanges is called even if the current value of the property is the same as its original value.

Current values: Property Id has value 1 Property Name has value FrankyProperty Version has value System.Byte[] Property PrincessId has value 1
Original values: Property Id has value 1 Property Name has value BinkyProperty Version has value System.Byte[] Property PrincessId has value 1
Database values: Property Id has value 1 Property Name has value Squeaky Property Version has value System.Byte[] Property PrincessId has value 1

Setting Values From Another Object
Current values: Property Id has value 1 Property Name has value Rapunzel
Original values: Property Id has value 1 Property Name has value Rosannella

Getting & Setting Complex Pro’s

Dynamic Proxies
When creating instances of POCO entity types, the EF often creates instances of a dynamically generated derived type that acts as a proxy for the entity.
This proxy overrides some virtual properties of the entity to insert hooks for performing actions automatically when the property is accessed.Configuration.ProxyCreationEnabled = true;

Creating an Instance of a Proxy
The Create method does not add or attach the created entity to the context.
If the entity type is sealed and/or has no virtual properties then Create will just create an instance of the entity type.

Automatically Detecting Changes
DbContext automatically detecting changes when the following methods are called:
DbSet.Find
DbSet.Local
DbSet.Remove
DbSet.Add
DbSet.Attach
DbContext.SaveChanges
DbContext.GetValidationErrors
DbContext.EntryDbChangeTracker.Entries

Disabling Auto Detecting Changes
performance improvements
An alternative to disabling and re-enabling is to leave automatic detection of changes turned off at all times and either call context.ChangeTracker.DetectChangesexplicitly.

http://blogs.microsoft.co.il	1311
http://www.e4d.co.il	139
http://feeds2.feedburner.com	35
http://e4d.co.il	22
http://localhost	8
http://beta.blogs.microsoft.co.il	7
http://translate.googleusercontent.com	2
http://207.46.192.232	1
http://feeds.feedburner.com	1

Entity Framework - Object Services

by Eyal Vardi on Oct 14, 2011

Accessibility

Categories

Tags

Upload Details

Usage Rights

9 Embeds 1,526

Statistics

Entity Framework - Object Services — Presentation Transcript