Migrations in Entity Framework Core are a way to apply changes to your database schema based on the changes made to your data model. When you modify your model classes, you can create a migration to update the database accordingly. The .NET Command Line Interface (CLI) provides a simple command to create a new migration. This guide will walk you through the steps to create a new migration using the CLI.

What is a Migration?

A migration is a set of instructions that Entity Framework Core uses to update the database schema. Migrations can include creating tables, adding columns, modifying data types, and more. Each migration is represented by a class that inherits from Migration and contains methods to apply and revert the changes.

How to Create a New Migration

To create a new migration using the CLI, follow these steps:

Step 1: Open Your Command Line Interface

Open your terminal (macOS/Linux) or command prompt (Windows).

Step 2: Navigate to Your Project Directory

Use the cd command to navigate to the directory of your ASP.NET Core project that contains the DbContext class. For example:

cd /path/to/your/MyWebApp

Step 3: Run the dotnet ef migrations add Command

Use the following command to create a new migration:

dotnet ef migrations add MigrationName

In this command, replace MigrationName with a descriptive name for your migration. It's a good practice to use a name that reflects the changes being made, such as AddNewColumn or UpdateCustomerTable.

Example

Suppose you want to create a migration to add a new column to the Products table. You would execute the following command:

dotnet ef migrations add AddProductDescription

After executing this command, you should see output indicating that the migration has been created successfully. The migration files will be located in the Migrations folder of your project.

Verifying the Migration

To verify that the migration has been created, you can navigate to the Migrations folder in your project. You should see a new file named something like 20230315123456_AddProductDescription.cs, where the prefix is a timestamp indicating when the migration was created.

Open the migration file to see the generated code, which will include the Up and Down methods. The Up method contains the code to apply the migration, while the Down method contains the code to revert it.

Applying the Migration

After creating the migration, you can apply it to the database using the following command:

dotnet ef database update

This command updates the database schema to match the current model, applying any pending migrations.

Conclusion

Creating a new migration using the CLI is a straightforward process that helps you manage changes to your database schema effectively. By following the steps outlined in this guide, you can easily create migrations that reflect changes in your data model, ensuring that your database remains in sync with your application. Understanding how to work with migrations is essential for any developer using Entity Framework Core in their ASP.NET Core applications.