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We know that our application is persisting data, but how is this working? And where is our database?
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When we updated the console lab to use
our context we saw that a comic book with
0:00
the series title The Amazing Spider-Man
was added every time that we ran our app.
0:05
So, we know that our application is
persisting data but, how is this working?
0:11
And where is our database?
0:16
We can see the database
that EF is creating for
0:18
us by using Visual Studios Sequel Server
optic explorer.
0:21
Press control Q to place the focus
in the quick launch search box.
0:25
Type sql server and
select the first item in the list.
0:30
Under the SQL server node,
0:35
we can see a list of the SQL server
instances that we're connected to.
0:37
If you don't see the MS SQL
local DB instance,
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click the add SQL server
icon to connect to a server.
0:45
Click on local, then MS SQL local DB.
0:49
The authentication field should
be set to Windows authentication
0:53
meaning to use our current
Windows account name.
0:58
Username and
1:01
password should be disabled as they're
not used with Windows authentication.
1:01
And the database field can be left blank.
1:07
Click Connect to connect to the server.
1:10
Once the server appears in the list you
can double-click the server name and
1:13
then the database's folder to see a list
of the servers available databases.
1:17
The ComicBookGalleryModel.Context database
is the database that EF created for
1:22
our application.
1:27
EF name the database by combining
our Visual Studio project name with
1:29
our context class name,
separated by a dot.
1:33
Double click the database and
1:37
then the tables folder to see
a list of the databases tables.
1:38
Our database currently has two tables.
1:43
dbo.__MigrationHistory and dbo.ComicBooks.
1:47
The dbo prefix that appears
before the table names
1:54
is the name of our database
is default schema.
1:58
A schema is a distinct namespace
similar to C# name spaces
2:00
to facilitate the separation and
management of database objects.
2:05
For our purposes in this course,
we'll stick with using the dbo Schema.
2:10
For more information about database
Schemas, see the teachers notes.
2:14
If we double click
the comicbook table name,
2:18
Visual Studio will open
a design view of the table.
2:20
In the top half of the tab is a list of
the table column names and data types.
2:23
Along with whether or not,
the column allows no values.
2:29
The in four card data type is
a variable length Unicode string,
2:33
the max part within the parentheses,
indicates that the column can contain
2:37
a string as large as the maximum allowed
size, which is a very large strain,
2:42
two gigabytes or
approximately a billion characters.
2:47
We'll see in the next section how we
can refine our data model and restrict
2:52
the allowable number of characters to
a more specific reasonable number.
2:56
In the bottom half of the tab is the sql
statement that would create our table.
3:00
We can also expand the arrow
to the left of the table name
3:06
in the sql server object explorer window,
and
3:09
double click the columns folder to
see a list of the table columns.
3:13
This gives us three different ways
to review the design of our table.
3:16
For now,
let's ignore the migration history table,
3:21
we'll come back to it at
the end of the section.
3:24
Okay, we know where our databases and
what it generally looks like,
3:27
but how did it get created?
3:32
How do we get from our
model to a database?
3:34
The first time that we access the context's comic books db set property,
3:38
EF will check of the database exists and
if it doesn't exist, it will create it.
3:43
When creating the database, EF will use
our model to determine what tables and
3:49
table columns to generate.
3:54
Remember that EDMX file that we
briefly reviewed in the first section?
3:57
When using the code first workflow,
4:01
EF generates an in memory version of
the EDMX file using type discovery.
4:04
Type discovery is the process that EF
uses to discover all of the entities that
4:09
are part of our model.
4:14
[SOUND] EF starts with compiling
a list of the entities that have DbSet
4:16
properties defined in our context.
4:20
From there, it'll walk the available entity relationships to discover any
4:23
entities that aren't represented by dbset properties.
4:28
Our model currently doesn't have any entity relationships.
4:32
We'll see examples of relationships
in the next section for each entity.
4:36
EF also compiles a list of the properties,
and for
4:41
each property various characteristics, such as its data type and nullability.
4:45
All of this information about our
entities makes up what is called
4:51
in EDMX terms the conceptual model.
4:55
EF then uses a set of conventions to
generate the database representation
4:58
of the conceptual model.
5:03
That's called the storage model.
5:05
And then, map the conceptual
model to the storage model.
5:08
The default convention is for
5:12
the entity to be represented
by a table in the database.
5:14
The name of the table is
either the singular or
5:18
plural version of the entity class name.
5:21
Depending upon whether or
5:23
not EF has been configured to use
the pluralizing table name convention.
5:25
If EF finds a property on the entity whose name matches the convention of ID,
5:30
ID, class name ID or
class name ID then EF will add a primary
5:36
key column to the table with
the same name and data type.
5:41
If the property's data type is numeric or
a globally unique identifier or
5:45
GUID, then EF will also make
the column an identity column.
5:51
For more information about GUIDs,
see the teacher's notes.
5:55
As mentioned in an earlier video,
5:59
identity columns are automatically
assigned values by the database.
6:01
When new records are added to the table.
6:06
EF also adds an entity property that has a setter, public protected or
6:09
private as a table column.
6:13
Mapping the Property's Name
to the Column Name and
6:15
the property's .NET Data Type to the
appropriate SQL Server Column Data Type.
6:18
The column's nullability
is determined by evaluating
6:23
if the .NET data type is nullable or not.
6:27
So, a column mapped from a property with
a data type of int wouldn't allow nulls.
6:30
Whereas a column mapped from a property
with a data type of string would.
6:36
The conventions that EF uses, including
all of the conventions that we've
6:41
discussed, can be customized to
fit your particular requirements.
6:45
So far,
most of these conventions make sense for
6:49
our application, though we've already seen
how the text-base columns in the comick
6:52
book table could be refined to use
a more specific allowable string length.
6:58
We'll see examples of how to customize or
7:03
override the default conventions
in the next section.
7:05
But first, let's see in the next video how
we can change the name of our database.
7:09
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