Understanding Code First Approach of Entity Framework Core

Introduction

In this article, we will understand the Code First approach of Entity Framework Core in ASP.NET Core. The examples show how to create tables, delete tables, add columns, remove columns, change column size, make columns not null, add primary keys, and create relationships.

Topics Covered

• What is Entity Framework Core?
• Create a new ASP.NET Core project
• Set up Entity Framework Core and add a new table
• Add a new column in a table
• Delete a column from a table
• Change column size
• Make a column not null
• Delete a table
• Add a primary key column
• Add a relationship (foreign key)

What Is Entity Framework Core?

Entity Framework Core is the newer version of Entity Framework after EF 6.x. It is open-source, lightweight, extensible, and cross-platform.

It is an object-relational mapping framework that helps developers access and store data in a database without writing all the data access code manually.

Create a New ASP.NET Core Project

Step 1

Open Visual Studio and create a new project.

Step 2

Select an ASP.NET Core project and click Next.

Step 3

Enter the project name and location, then click Create.

Step 4

Choose the .NET Core framework and an empty template, then click Create.

Set Up Entity Framework Core and Add a New Table

Step 1

Install the required NuGet packages.

The article uses these packages:

• Microsoft.EntityFrameworkCore.SqlServer
• Microsoft.EntityFrameworkCore.Tools
• Microsoft.Extensions.Configuration

Step 2

Create a Model folder for your entity classes.

Step 3

Add a Book entity class with your desired properties.

Step 4

Add a context class that inherits from DbContext.

Add a constructor that accepts DbContextOptions and passes it to the base constructor, then add a DbSet<Book> property.

Step 5

Add the connection string to appsettings.json.

The article uses a local SQL Server connection and Windows authentication.

Step 6

Register the DbContext in Startup.

The article adds CFDbContext in ConfigureServices and reads the connection string using GetConnectionString.

Step 7

Open Package Manager Console.

Step 8

Create the first migration.

The migration creates a snapshot file and the initial migration file.

Step 9

Apply the migration.

The Books table is now created in SQL Server. By default, a property named Id becomes the primary key, and string properties map to nvarchar(max).

Add a New Column in a Table

Step 1

Add a new property to the model, such as BookLanguage.

Step 2

Create a new migration.

Step 3

Apply the migration.

The new column appears in the Books table.

Delete a Column from a Table

Step 1

Remove or comment out the property from the model.

Step 2

Create a migration for the removed column.

Step 3

Apply the migration.

The column is removed from the table.

Change Column Size

Step 1

Add the MaxLength attribute to set the size of a column.

Step 2

Create a migration for the size change.

Step 3

Apply the migration.

The column now has the configured size.

Make a Column Not Null

Step 1

Add the Required attribute to the property.

Step 2

Create a migration.

Step 3

Apply the migration.

The column no longer accepts null values.

Delete a Table

Delete a table by removing or commenting out the DbSet from the context file, then add a migration and update the database.

After applying the migration, the table is removed from SQL Server.

Add a Primary Key

In EF Core, a property named Id becomes the primary key automatically. If you want another column to be the primary key, add the Key attribute.

Step 1

Add Key to the column that should be the primary key.

Step 2

Create the migration.

Step 3

Apply the migration.

The EmpId column is now the primary key.

Add a Relationship (Foreign Key)

The article adds a Department model with DepartmentId and DepartmentName, then creates a relationship from the employee table.

Step 1

Add the foreign key property and the navigation property to the employee model. The article notes that if the column name does not match the expected primary key pattern, you should specify it in the ForeignKey attribute.

Step 2

Create a migration for the relationship.

Step 3

Apply the migration.

The relationship is now present in SQL Server.

Conclusion

Entity Framework Core Code First makes it straightforward to evolve your database through your C# model classes and migrations. You can add columns, remove columns, change sizes, add constraints, delete tables, and define relationships with a simple workflow.