Using Data Annotations to Refine the Generated Database

Now that we have our entity relationships defined, 0:00 we can turn our attention to making some much needed database refinements. 0:03 Let's start by taking a look at how we can refine our model 0:07 by using data annotation attributes on our entity class properties. 0:11 The Artists Name database table column has a data type NVARCHAR (MAX) and 0:16 currently allows nulls. 0:21 To review, the NVARCHAR data type is a variable length Unicode string. 0:24 The MAX part within the parentheses indicates that the column can contain 0:29 a string as large as the maximum allowed size, 0:33 which is 2 gigabytes or approximately a billion characters. 0:37 We can use data annotation attributes to influence how EF will generate the Artists 0:41 database table. 0:46 As we discussed in an earlier video, EF is using the .NET data types nullability to 0:51 determine if the database column should allow nulls. 0:56 The .NET string data type is nullable. 0:59 So EF will by default make all string-based database columns nullable. 1:03 To let EF know that the name property should not allow nulls, 1:09 we can decorate it with the required data annotation attribute. 1:12 Be sure to add the using directive for 1:19 the System.ComponentModel.DataAnnotations namespace. 1:21 We can also let EF know what the maximum allowable number of characters 1:26 should be for this property by adding the StringLength attribute. 1:30 The StringLength attribute accepts some maximum length parameter, which I'll set 1:36 to 100, which seems like a reasonable maximum length for this property. 1:41 It's worth noting that we can also use the MaxLength 1:46 attribute to specify the maximum length. 1:49 Unfortunately, the MaxLength attribute doesn't work with ASP.NET MVC validation, 1:51 whereas the StringLength attribute does. 1:57 So while either would work fine for our console app, I prefer to use StringLength. 2:00 Which will make our code more easily ported to an MVC app later on, if or 2:05 when we choose to do that. 2:10 Let's add the same attributes to the Role entity class' Name property. 2:13 And the Series entity class' Title property. 2:32 Before we test our changes, 2:42 let's look at a few of the other data annotation attributes that we can use. 2:44 We already saw how we can change the foreign key property name 2:51 by using the foreign key attribute. 2:54 In a similar vein, we can customize the name of the database table 2:56 by using the Table attribute, Table, 3:00 And how about Talent, for our new database table name? 3:07 The attribute is in a different namespace. 3:15 So we'll need to add a using directive for 3:18 the System.ComponentModel.DataAnnotations.Sc- 3:21 hema namespace. 3:24 We can also customize the name of a column using the Column attribute, Column, 3:28 And let's change the name of the column to FullName. 3:38 The Table and Column attributes aren't typically used when you're 3:44 using EF to generate your database. 3:49 But they're useful when working with an existing database, and you want to use 3:52 entity class or property names that are different from their associated table or 3:57 column names, We can also use the NotMapped 4:01 attribute to tell EF to ignore any settable properties on our entity class. 4:07 I'll add a string property named Test, 4:14 And decorate it with the NotMapped attribute. 4:20 EF will automatically ignore any properties that don't have a setter. 4:24 So it's redundant to decorate read-only properties with the NotMapped attribute. 4:28 Now let's test our model changes. 4:33 Our console output still looks like we expect it to. 4:38 Let's review the generated database. 4:41 If you have the Tables folder open, be sure to refresh it. 4:47 Notice that we now have a Talent table instead of an Artists table. 4:53 And it contains a FullName column instead of a Name column. 4:59 Also the column's data type is now nvarchar(100) instead of nvarchar(MAX). 5:04 And the column no longer allows nulls. 5:11 And the Series, Title, and Roles Name columns have been updated as well. 5:14 And our test property that we added to our Artist entity class was ignored by EF. 5:28 Now that we've seen how the Table, Column, and 5:36 NotMapped attributes work, let's remove them from our Artist entity class. 5:39 We can also remove the using directive for 5:50 the System.ComponentModel.DataAnnotations.Sc- 5:52 hema namespace, and our test property. 5:54