What is Entity Framework Core Seed Data in C#?

Entity Framework Core Seed Data in C# is a feature that allows developers to prepopulate a database with initial or default data during database initialization. Seed data is essential when you want to ensure that your database starts with specific records, such as default user roles, configuration settings, or reference data.

Here’s how Entity Framework Core Seed Data works:

1. DbContext Configuration: To use seed data, you first define it within your DbContext class, which represents the database context in your application. Inside the DbContext class, you override the `OnModelCreating` method.

2. Model Configuration: Inside the `OnModelCreating` method, you use the Fluent API or Data Annotations to configure the database model. This includes defining entities, their properties, relationships, and any other database-specific settings.

3. Seed Data Definition: After configuring your database model, you can define the seed data using the `HasData` method. This method is typically applied to the entity configurations within the `OnModelCreating` method. You provide an array or collection of objects that represent the initial data you want to insert into the corresponding database table.

4. Migration and Update: Once you’ve defined your seed data, you need to create a database migration using Entity Framework Core’s migration tools. This migration will capture the changes required to apply your model configuration and seed data to the database.

5. Database Initialization: During database initialization (typically when your application starts or when a new database is created), Entity Framework Core checks if any migrations are pending. If there are pending migrations, it applies them, which includes executing the code to insert the seed data into the database.

6. Use Cases: Seed data is valuable for scenarios where you need to ensure that certain records exist in the database from the very beginning. For example, you might seed a list of default user roles, categories, or settings. This ensures that your application can run smoothly and consistently without manual data entry.

7. Maintenance: Over time, if you need to update or extend your seed data, you can create new migrations to modify the existing data or add new records. Entity Framework Core’s migrations allow you to evolve your database schema and seed data as your application evolves.

Entity Framework Core Seed Data simplifies the process of initializing a database with predefined data, making it a powerful tool for ensuring data consistency and providing a smooth experience for your application users.