Introduction
This
article introduces Entity Framework to absolute
beginners. The article is meant for developers who are primarily using ADO.NET
to write their data access layers. Many experienced developers will find this
article very basic but since the article is written from the perspective of
beginners, I've tried to keep things simple.
Background
ADO.NET is
a very strong framework for data access. ADO.NET has been around since many years and
there are a lot of systems running over ADO.NET. Developers who are totally
oblivious to the concept of ORMs will probably be asking "What is Entity
Framework? What are the benefits of using it and is it an alternative to
ADO.NET?"
Well, to
answer the first question about what is Entity Framework, Entity Framework is
an Object Relational Mapper(ORM). It basically generates
business objects and entities according to the database tables and provides the
mechanism for:
1. Performing
basic CRUD (Create, Read, Update, Delete) operations.
2. Easily
managing "1 to 1", "1 to many", and "many to
many" relationships.
3. Ability
to have inheritance relationships between entities.
and to
answer the second question, the benefits are:
1. We
can have all data access logic written in higher level languages.
2. The
conceptual model can be represented in a better way by using relationships
among entities.
3. The
underlying data store can be replaced without much overhead since all data
access logic is present at a higher level.
and
finally, the last question that whether it is an alternative to ADO.NET, the
answer would be "yes and no". Yes because the developer will not be
writing ADO.NET methods and classes for performing data operations and no
because this model is actually written on top of ADO.NET, meaning under this
framework, we are still using ADO.NET. So let us look at the architecture of
Entity Framework (diagram):
Using the code
Let's
try to understand the ease of use that Entity Framework provides by performing
simple CRUD operations. Once we look at the code and how effortlessly and
efficiently we can do these operations, the benefits of Entity Framework will
become quite obvious.
Creating the
database
Let's
have a simple database with one table. Let's create a simple table for Contacts
and we will perform CRUD operations on this table.
Adding the Entity Model to the Website
Once we have the
database ready, we can add the entity model to our website. We can do this by
adding anADO.NET Entity Data Model to the website.
Once we select to add
this data model to our website, we will have to select the approach we want to
take for our Model's contents.
What
this selection means is that we can either choose to generate the entity model
from an existing database schema or we can design the entity model here and
then later hook it up to the database. Since we already have the database
ready, we will use the first option. Once the Model is generated, the Entity
for each table is generated. The generated entity for our contact table is:
Also,
the classes for performing database operations are also created. We just need
to know how to use these classes to perform database operations.
Insert operation
Let us create a simple
page to perform an insert operation.
Now once
the user chooses to insert the values into the database, the actual data
operation can be performed by using the AddObject method of
the Model class entity collection. The following code snippet show how to
perform the insert.
Contact
con = new Contact();
con.fname
= TextBox1.Text;
con.lname
= TextBox2.Text;
con.phone
= TextBox3.Text;
ContactsDb
db = new ContactsDb();
db.Contacts.AddObject(con);
db.SaveChanges();
This will insert the
record into the table. You can notice the simplicity and efficiency of the code
we wrote to perform the insertion.
Reading all the records
There are scenarios
when we want to read all records. Let's say we are making a page that will
display all the contact information in a single page.
We can retrieve the
collection of Entities using the Model object to achieve this. The code snippet
below will show how that can be done.
ContactsDb
db = new ContactsDb();
Repeater1.DataSource
= db.Contacts;
Repeater1.DataBind();
Selecting a specific record
If we want
to select a specific record from the table, we can use the SingleOrDefault method on the Model's entities
collection. Let's say we want the functionality of updating/deleting a record
on a single page then we will first have to select the record based on the ID,
then update/delete the selected record.
Selection of any particular record (Contact) based on ID can be done as:
int idToupdate =
Convert.ToInt32(Request.QueryString["id"].ToString());
ContactsDb
db = new ContactsDb();
Contact
con = db.Contacts.SingleOrDefault(p => p.id == idToupdate);
Once this
code is executed, the Contact object will contain the required values.
Updating the record
If we want to update a record, then
a simple update operation can be performed as:
int idToupdate =
Convert.ToInt32(Request.QueryString["id"].ToString());
ContactsDb
db = new ContactsDb();
Contact
con = db.Contacts.SingleOrDefault(p =>
p.id == idToupdate);
con.phone
= TextBox1.Text;
db.SaveChanges();
Once this code executes, the value
of phone number will be updated by a new value which is retrieved fromTextBox1.
Deleting a record
If we want
to delete a particular record then we can perform a delete operation by using
the DeleteObject function. The following code snippet
demonstrates the same:
//delete this contact
int idToupdate =
Convert.ToInt32(Request.QueryString["id"].ToString());
ContactsDb
db = new ContactsDb();
Contact
con = db.Contacts.SingleOrDefault(p => p.id == idToupdate);
db.Contacts.DeleteObject(con);
db.SaveChanges();
Now that we have the basic CRUD
operations performed on the database using the Entity Framework.
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