The Code First approach in Entity Framework is a development approach where you create your domain classes first and then generate the database schema based on those classes. This approach allows you to focus on the object-oriented design of your application without worrying about the underlying database schema.
To use the Code First approach, you define your classes with properties that map to database columns and relationships between classes. You can then use the Entity Framework to generate a database schema based on these classes. The generated schema can be customized using data annotations or fluent API to configure data types, indexes, constraints, etc.
This approach provides flexibility, maintainability, and faster development as you can easily modify the domain classes and regenerate the database schema. It's a popular choice for greenfield development where there's no pre-existing database schema to work with.
To use Code First, you need to define a context class that inherits from the DbContext class provided by Entity Framework. The context class is responsible for managing the database connection, translating data between the database and your application, and executing queries.
You can configure the context class to specify the database connection string and also to include or exclude the entities you want to map to the database. You can also use the context class to seed the database with initial data, create and update the database schema, and more.
One of the main benefits of the Code First approach is that it allows you to use a Domain Driven Design (DDD) approach to your application design. You can define your domain entities as POCOs (Plain Old C# Objects) without worrying about the underlying database schema, and then use the Entity Framework to generate the database schema based on those entities.
Overall, the Code First approach in Entity Framework provides a flexible, maintainable, and efficient way to develop data-driven applications using object-oriented principles.