Entity Framework

Agenda
• A brief history…
• What’s an ORM?
• Entity Framework Architecture
• DB First / Model First and the (in)famous EDMX
• Inheritance
• Code First / Code Second
• Eager / Lazy & Explicit Loading
• Performance / Profiling
204/10/2013 Entity Framework Training

A brief history…
EF releases and versioning is a bit of a mess :-)
• EF aka EF1 aka EF 3.5 was released with . NET 3.5 (VS2008)
• Basic ORM functionalities / DB first only
• EF 4 was released with . NET 4.0 (VS2010)
• POCO support / Lazy loading
• EF 4.1
• DBContext API / Code First / Nuget package
• EF 4.1.1 and then EF 4.2
• Mainly bug fixes
• EF 4.3
• Code First Migration
• EF 4.3.1
• Bug fixes / better LocalDB support

A brief history…
MS guys were the first to admit that this versioning was not clear and that’s why
they rationalize how they were naming and distributing their releases
• EF 5
• This release can be used in Visual Studio 2010 and Visual Studio 2012 to write
applications that target .NET 4.0 and .NET 4.5
• But when targeting .NET 4.5 you have enum support / table-valued functions /
performance improvements / multiple-diagrams per model
• EF 6
• Async Query and Save / Testability improvements / DbSet.AddRange &
RemoveRange / DbChangeTracker.HasChanges / Dependency Resolution / Code
First Mapping to Insert/Update/Delete Stored Procedures / …
Have a look at this post on ADO .NET Blog where MS guys were calling for
feedback about versioning issues

What’s an ORM?
ORM stands for Object-Relational Mapping.
According to Wikipedia’s page :
ORM is a programming technique for converting data between incompatible type
systems in object-oriented programming languages. This creates, in effect, a
"virtual object database" that can be used from within the programming language.
©2010 J. Lerman

EF Architecture
©2013 MSDN

EF Architecture
• Object Services
• This is where the DBContext is, which represents the session of interaction between
the applications and the data source. It provides the facilities for tracking changes
and managing identities, concurrency, and relationships. And save changes towards
the DB.
• EntityClient Data Provider
• This provider manages connections, translates entity queries into data source-
specific queries, and returns a data reader that the Entity Framework uses to
materialize entity data into objects.
• Data Providers
• This is the lowest layer which translates L2E queries via command tree to native
SQL expression and executes it against the specific DBMS system

DB First / Model First
The simplistic view:
©2013 Web Camps Team
It seems like that’s a 1 to 1 relationship between DB model and EDM, that they’re
tied together, but it’s not.
It’s not even mandatory to have your DB generated based on your Entity Data
Model, they could be different and live their own life, this is what mapping is for!

DB model VS Conceptual model
• A DB model is designed to address storage problems. It’s also optimized to deal
with performance while fetching data.
• A Business object model is designed to handle business needs.
• They should not look like each other!
• Entity Framework allow you to do so. Whatever approach you’ll choose, you’ll
be able to isolate both models and handle the mapping, well… in the mapping
layer ;-)

DB model VS Conceptual model
Please read this pretty interesting article where Rowan Miller and José A. Blakeley
answer that question: “Do we still have an impedance mismatch problem? “
To conclude, I’d like to quote that comment I found on an article about impedance
mismatch, that somehow summarizes some useless debates:
“RDBMS has its advantages, OOP has its advantages, and SOA also has its
advantages. These things aren't just useless extra "layers", they're tools which all
serve different purposes (RDBMS for working with large datasets, SOA for
implementing complicated business rules, OOP for writing more type-safe and
maintainable code).
If you stop viewing these concepts as being at war with each other and start
viewing them as different perspectives of the same solution, all the long-winded
arguments about OOP and ORM and whatever start to look a lot more like lame
excuses for ordinary human inertia (i.e. the overwhelming urge to keep doing
things the way you're doing them now, at any cost).” ;-)

The (in)famous EDMX
An EDMX file is just an XML file.
Just give that a try: Right-click on one EDMX file in Visual Studio and choose “Open
with…” menu option and select the XML entry as follows:

The (in)famous EDMX
As I said, EDMX is just an XML file:
1204/10/2013
An EDMX is a combination of 3 different parts that make up the whole thing:
• <edmx:StorageModels> aka the SSDL
• <edmx:ConceptualModels> aka the CSDL
• <edmx:Mappings> aka the MSL
…you can even edit those sections manually, but at your own risk! :-)

The (in)famous EDMX
1304/10/2013
By default, the EDMX is embedded in the project assembly it belongs to:
The connection string will look like this:
Entity Framework Training

The (in)famous EDMX
14
It’s also possible to generate CSDL, SSDL & MSL by changing the "Meta Artifact
Processing" property of your model to "Copy to Output Directory".
3 separate XML files
Yes, it can be useful in some particular cases…
The connection string will look like as right below, did you notice the changes?
Last piece of advice, if you want to edit the XML files by yourself, checkout the
cookbook first! ;-) Entity Framework Training

The (in)famous EDMX
1504/10/2013
You might want to have a look at the Edmgen2 tool.
As written on the Edmgen2 homepage :
EdmGen2 is a command-line tool for the Microsoft ADO.NET Entity Framework.
EdmGen.exe can only read and write the CSDL, SSDL & MSL file formats. However,
EdmGen2.exe can read and write the EDMX file format used by the Visual Studio
design tools.
Additionally, EdmGen2.exe contains some experimental functionality not found in
EdmGen.exe. […] with the ability to identify inheritance relationships in relational
database schema […] and constructs a suitable model and mapping,
To be complete, have a look at this article to see the changes that were made to
the EDMX schema since V1 specifications to the current V3.

The (in)famous EDMX
1604/10/2013
The goal of this training is not to learn how to manipulate the Entity Data Model
Designer in Visual Studio, you certainly all know at least the basic features.
If you need to go into further details, have a look a this MSDN Library article called
“Modeling and Mapping with Entity Framework Designer”. It contains everything
you’ll need to be able to map CSDL with SSDL like a chef!
By the way, now you should understand easily why the CSDL is not always updated
even if you perform an “Update Model From DB Wizard” towards the EDMX. It will
work only in case of new things added in the DB model. As I said, CSDL and SSDL
must live their own life. Entity Framework cannot decide for you whether it needs
to remove an entity property if one column has been altered/deleted in the DB.
Every modification made in your DB schema should impact your MSL rather than
your CSDL.

The (in)famous EDMX
1704/10/2013
• Table-per-concrete class mapping.
• Unmapped abstract types. When you
create an abstract entity type with the
Entity Designer, the type must be mapped
to a table or view.
• Creating conditions on association
mappings.
• Mapping associations directly to stored
procedures. Mapping many-to-many
associations is not supported.
• Creating conditions on Function
Import mappings.
• Annotations.
• Query views.
• Models that contain references to other
models.
• Creating associations without
corresponding navigation properties.
• Adding or editing storage model objects.
(Deleting storage model objects is
supported.)
• Adding, editing, or deleting functions that
are defined in the conceptual model.
One thing you should know about the Entity Designer is that it has some limitations…
But things are getting better, have a look at the J. Lerman article about the new
Entity Designer in VS2012, more to come with VS2013 and EF6, stay tuned!

Inheritance
1804/10/2013
Before going further and see what Code First is all about, let’s talk about table
inheritance.
Like with classes in OOP, in a conceptual model you can define an entity type (a
derived type) that inherits from another entity type (the base type). However,
unlike classes in object-oriented programming, in a conceptual model the derived
type always inherits all the properties and navigation properties of the base type.
You cannot override inherited properties in a derived type. © MSDN
There are three main Inheritance Mapping strategies:
• Table Per Hierarchy (TPH)
• Table Per Type (TPT)
• Table Per Concrete Class (TPC)
They have all their pros & cons and it will be up to you to choose the right one!

Inheritance
1904/10/2013
Let’s see how those mapping strategies work with the simple example from the
Ado.Net Blog.
The entities:

Inheritance
2004/10/2013
 Table Per Hierarchy (TPH)
TPH inheritance uses one database table to maintain data for all of the entity types
in an inheritance hierarchy.
The table contains a column which I have named ‘Type’. This column acts as the
discriminator, which helps determine the whether a bike is a TTBike or a
MountainBike.

Inheritance
2104/10/2013
 Table Per Type (TPT)
In TPT there is a base table which stores all of the common information. There is
also one or more derived entities which store the attributes that are unique to that
derived entity.
The EF Designer uses the TPT strategy by default and so any inheritance in the
model will be mapped to separate tables.

Inheritance
2204/10/2013
 Table Per Concrete Class (TPC)
Table per Concrete class creates a table for each derived (or concrete) entity and
does not create a table for the base abstract entity.
TPC is supported by the Entity Framework at runtime but are not supported by the
EF Designer. If you want to use TPC you have two options: use Code First, or
manually edit the EDMX file.

Inheritance
2304/10/2013
If you have a conceptual model with object inheritance, use the
OfType<TResultType> to limit the query to only result of a specific type.
foreach (var course in department.Courses.OfType<OnlineCourse>())
{
Console.WriteLine(" Online - {0}", course.Title);
}
Anyway, before going on and implementing one of those inheritance mapping
strategies, ask your DBA first! ;-)

Mapping
2404/10/2013
We just saw that it was kinda easy to map a DB model with an Object model that
are different (and should stay different).
And it’s even easier with Code First / Code Second approaches! But we’ll see that
just after.
But there’s one important thing to mention: We all agree that DB model should
not drive the way we design our Object model. But it should neither be the case
the other way round!
If you modified your Object model, don’t take the T-SQL scripts EF will generate to
update your DB accordingly, for granted.
Ask your DBA if it’s ok or not before validating any changes in the DB schema!
They know better than EF ;-)

Code First / Code Second
2504/10/2013
Code First approach lets you define your conceptual model and mapping to the DB
model using code only. With Code First, you get rid off the EDMX!
What’s Code Second?
It’s pretty much the same, it means only that you can do it with an existing DB.
How?
Using the EF Power Tools and use the Reverse Engineer Code First option!
By the way EF Power Tools offers other great features:
• Reverse Engineer Code First
• Customize Reverse Engineer Templates
• View Entity Data Model(Read-only) / XML / DDL SQL
• Generate (pre-compiled) views
Easy!

Code First / Code Second
2604/10/2013
Let’s see how Code First works…
 Create your classes:
public class Blog
{
public int BlogId { get; set; }
public string Name { get; set; }
public virtual List<Post> Posts { get; set; }
}
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public int BlogId { get; set; }
public virtual Blog Blog { get; set; }
}
 Create your context :
public class BloggingContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }
public DbSet<Post> Posts { get; set; }
}
Yeah, it’s that easy!
By convention DbContext has created a database for you.
 Store data
using (var db = new BloggingContext())
{
var blog = new Blog { Name = « MyBlog » };
db.Blogs.Add(blog);
db.SaveChanges();
}

Code First / Code Second - Conventions
2704/10/2013
EF was able to create a DB based on the model because it uses conventions!
• Primary Key Convention
• If a property on a class is named “ID” or <className>ID:
public int DepartmentID { get; set; }
• Type Discovery
• Your context exposes DbSet properties for the types that you want to be part of the model. Code
First will include these types and also will pull in any referenced types, even if the referenced
types are defined in a different assembly.
• If your types participate in an inheritance hierarchy, it is enough to define a DbSet property for
the base class, and the derived types will be automatically included, if they are in the same
assembly as the base class.
• Complex Types Convention
• If no primary key can be inferred then the type is automatically registered as a complex type
OVER

2804/10/2013
• Relationship Convention
• Any property with the same data type as the primary key and with a name like:
• <navigation property name><principal primary key property name>
• <principal class name><primary key property name>
• <principal primary key property name>
will represent a Foreign Key public class Department
{
// Primary key
public string Name { get; set; }
// Navigation property
public virtual ICollection<Course> Courses { get; set; }
}
public class Course
{
// Primary key
public int CourseID { get; set; }
// Foreign key
// Navigation properties
public virtual Department Department { get; set; }
}
• Code First infers the
multiplicity of the
relationship based on the
nullability of the foreign key
• If a foreign key on the
dependent entity is not
nullable, then Code First sets
cascade delete

2904/10/2013
• Connection String Convention
• DbContext uses the namespace qualified name of your derived context class as the database
name and creates a connection string for this database using either SQL Express or LocalDb.
• Removing Conventions
• You can tell EF not to use some conventions like this:
modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();
• Pluggable Conventions (EF6)
• Build your own ones!

Code First / Code Second - Annotations
3004/10/2013
If your classes do not follow any kind of EF conventions, you can use attributes called
DataAnnotations
One of the coolest thing about DataAnnotations is that it’s shared between other
frameworks like ASP .Net MVC!
If you set as property as required:
[Required]
The DB column will be set as “not null” and the MVC application will perform client
side validation, even dynamically building a message using the property and
annotation names.

Code First / Code Second - Annotations
3104/10/2013
Here’s the list of the most common DataAnnotations:
• Key: Primary key
• Required: Not null
• MaxLength and MinLength: Obvious ;-)
• NotMapped: Not need to be stored
• ComplexType: Entity without primary key
• ConcurrencyCheck: If someone has modified the data in the meantime, it will
fail and throw a DbUpdateConcurrencyException
• TimeStamp: Concurrency based on Timestamp
• Table and Column: change the name of the tables and columns
• DatabaseGenerated: computed properties
• InverseProperty and ForeignKey: Relationship attributes
For relationships, go there!

Code First / Code Second – Fluent API
3204/10/2013
We saw that Code First allows you to work with Conventions (over configuration) but
this approach will obviously fit only small projects or POCs.
DataAnnotations is pushing the mapping capabilities a step forward, but keep in mind
that it has limitations as well, here’s a non exhaustive list of what it cannot do:
• The precision of a DateTime property
• The precision and scale of numeric properties
• A String or Binary property as fixed-length
• A String property as non-unicode
• The on-delete behavior of relationships
• Advanced mapping strategies
Here comes the Fluent API! (here & here)
The DataAnnotations only cover a subset of the fluent API functionality!

3304/10/2013
The code first fluent API is most commonly accessed by overriding the
OnModelCreating method on your derived DbContext.

3404/10/2013
Each Builder can define their mappings

3504/10/2013
Doing that way, you can easily separate your mapping files from your model!
The code becomes clearer and no reference is made to any EF libraries when
you’re designed your business model. Which is not possible with DataAnnotations.
There are so many options that the Fluent API offers that it would take hours to
describe them.
Please go and read those 2 articles to go further in details with the Fluent API
• Configuring/Mapping Properties and Types with the Fluent API
• Configuring Relationships with the Fluent API

Code First – Migrations
3604/10/2013
A word on Code First Migrations.
Entity Framework Code First Migrations enable changes to your model to be
propagated to your database through code. It’s based on Active Record migrations
(the primary data access technology used by the Rails framework).
It’s an easy way to be able to generate the scripts needed to go from one version
of your DB model to the V+1 or to be able to downgrade a schema version as well.
I won’t go any further, but as it’s a really nice feature, go and see more details on
MSDN!

Eager / Lazy & Explicit Loading
3704/10/2013
Entity Framework allows you fetch for data and load their relationships in many
ways.
3 of them are:
• Eager Loading
• Lazy Loading
• Explicit Loading
Once again all of them have their pros & cons and should be used with attention!
What is the best choice between multiple requests against the database versus a
single request that may contain a large payload. It may be appropriate to use eager
loading in some parts of your application and lazy loading in other parts.
We’ll try to see that…

3804/10/2013
Let’s have a look at the Lazy Loading versus Eager Loading cheat sheet from MSDN
Seems that it won’t be a good option for our sites to switch on Lazy loading!

3904/10/2013
One good option seems to load exactly what we need.
But this can be done in several ways as well!
While including related entities in a query is powerful, it's important to understand
what's happening under the covers. Let’s look how the .Include() works…
As stated on MSDN:
It takes a relatively long time for a query with multiple Include statements in it to
go through our internal plan compiler to produce the store command. The majority
of this time is spent trying to optimize the resulting query. The generated store
command will contain an Outer Join or Union for each Include, depending on your
mapping. Queries like this will bring in large connected graphs from your database
in a single payload, which will acerbate any bandwidth issues, especially when
there is a lot of redundancy in the payload (i.e. with multiple levels of Include to
traverse associations in the one-to-many direction).
Customers.Include(c => c.Orders) (click if you dare!)

4004/10/2013
SELECT [Project1].[C1] AS [C1],
[Project1].[CustomerID] AS [CustomerID],
[Project1].[CompanyName] AS [CompanyName],
[Project1].[ContactName] AS [ContactName],
[Project1].[ContactTitle] AS [ContactTitle],
[Project1].[Address] AS [Address],
[Project1].[City] AS [City],
[Project1].[Region] AS [Region],
[Project1].[PostalCode] AS [PostalCode],
[Project1].[Country] AS [Country],
[Project1].[Phone] AS [Phone],
[Project1].[Fax] AS [Fax],
[Project1].[C2] AS [C2],
[Project1].[OrderID] AS [OrderID],
[Project1].[CustomerID1] AS [CustomerID1],
[Project1].[EmployeeID] AS [EmployeeID],
[Project1].[OrderDate] AS [OrderDate],
[Project1].[RequiredDate] AS [RequiredDate],
[Project1].[ShippedDate] AS [ShippedDate],
[Project1].[ShipVia] AS [ShipVia],
[Project1].[Freight] AS [Freight],
[Project1].[ShipName] AS [ShipName],
[Project1].[ShipAddress] AS [ShipAddress],
[Project1].[ShipCity] AS [ShipCity],
[Project1].[ShipRegion] AS [ShipRegion],
[Project1].[ShipPostalCode] AS [ShipPostalCode],
[Project1].[ShipCountry] AS [ShipCountry]
FROM ( SELECT
[Extent1].[CustomerID] AS [CustomerID],
[Extent1].[CompanyName] AS [CompanyName],
[Extent1].[ContactName] AS [ContactName],
[Extent1].[ContactTitle] AS [ContactTitle],
[Extent1].[Address] AS [Address],
[Extent1].[City] AS [City],
[Extent1].[Region] AS [Region],
[Extent1].[PostalCode] AS [PostalCode],
[Extent1].[Country] AS [Country],
[Extent1].[Phone] AS [Phone],
[Extent1].[Fax] AS [Fax],
1 AS [C1],
[Extent2].[OrderID] AS [OrderID],
[Extent2].[CustomerID] AS [CustomerID1],
[Extent2].[EmployeeID] AS [EmployeeID],
[Extent2].[OrderDate] AS [OrderDate],
[Extent2].[RequiredDate] AS [RequiredDate],
[Extent2].[ShippedDate] AS [ShippedDate],
[Extent2].[ShipVia] AS [ShipVia],
[Extent2].[Freight] AS [Freight],
[Extent2].[ShipName] AS [ShipName],
[Extent2].[ShipAddress] AS [ShipAddress],
[Extent2].[ShipCity] AS [ShipCity],
[Extent2].[ShipRegion] AS [ShipRegion],
[Extent2].[ShipPostalCode] AS [ShipPostalCode],
[Extent2].[ShipCountry] AS [ShipCountry],
CASE WHEN ([Extent2].[OrderID] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C2]
FROM [dbo].[Customers] AS [Extent1]
LEFT OUTER JOIN [dbo].[Orders] AS [Extent2] ON [Extent1].[CustomerID] = [Extent2].[CustomerID]
WHERE N'UK' = [Extent1].[Country]
) AS [Project1]
ORDER BY [Project1].[CustomerID] ASC, [Project1].[C2] ASC

4104/10/2013
Well, well, well… what are the options then?
• Try to reduce the number of Include statements in your query to just bring in
the data you need
• Break your query into a smaller sequence of subqueries
Rather than that: Do that:

4204/10/2013
And what is Explicit Loading exactly?
Even with lazy loading disabled it is still possible to lazily load related entities, but
it must be done with an explicit call. To do so you use the Load method on the
related entity’s entry.
var blog = context.Blogs.Find(1);
// Load the posts related to a given blog
context.Entry(blog).Collection(p => p.Posts).Load();
The Query method provides access to the underlying query that the Entity
Framework will use when loading related entities.
// Load the posts with the 'entity-framework' tag related to a given blog
context.Entry(blog)
.Collection(b => b.Posts)
.Query()
.Where(p => p.Tags.Contains("entity-framework")
.Load();

4304/10/2013
Wanna be the king of loading entities?
Go there!

Performance / Profiling
4404/10/2013
ORM’s are often considered by DBA’s as the evil!
One of their fears if the T-SQL generated by Entity Framework. We have seen that
in some examples we can only give them reason!
The T-SQL can be ugly and lead to really poor performance.
Here comes the profiling!
There’s a lot of tools that allow you to do so. Please read this article from Julie
Lerman where she explains how to perform profiling (see the comments as well).
Once again, do not hesitate to talk to your DBA for any kind of advice!

Performance / Profiling
45
There are also a lot of best practice when it’s time to solve performance issues.
Here’s an non exhaustive list of what can be done:
• Cold vs. Warm Query Execution
• (mapping) View generation
• Moving your model to a separate assembly
• Caching (objects , results, query plans & metadata)
• Complied & Auto-compiled queries
• NoTracking queries
• Inhetirance strategies
• Upgrade to EF5 ;-)
• Lazy vs Eager
• …
Go here & here & here for much more details!

Appendix
4604/10/2013
ADO .Net Blog
Julie Lerman’s Blog, Rowan Miller’s Blog, Arthur Vicker’s Blog, Alex Jame’s Blog
T4 Templates and the Entity Framework
Effort - Entity Framework Unit Testing Tool
What’s Best for Unit Testing in EF? It depends, dude!
Creating an Entity Framework Data Model for an ASP.NET MVC Application (1 of 10)
Add/Attach and Entity States
Table-Valued Functions (TVFs)
Extending And Customizing Code First Models – Part 1 Of 2
Code First Insert/Update/Delete Stored Procedure Mapping (EF6)
Me and Entity Framework on StackOverflow

Find out more
• On https://techblog.betclicgroup.com/

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