Entity Framework Core (EF Core) is a powerful object-relational mapper (ORM) from Microsoft, simplifying data access in .NET applications. It provides developers with the means to perform CRUD operations (Create, Read, Update, and Delete) without needing to know the intricate details of the underlying database. EF Core maps classes in the application to tables in the database, allowing developers to interact with the database in an object-oriented manner, enhancing productivity and reducing errors in data handling.
In typical scenarios, EF Core maps models directly to database tables, enabling easy manipulation of data stored in the database. But occasionally, there are cases where a model doesn’t perfectly correspond to a database table. For instance, you might want to represent data from a view or a complex query that doesn’t match the structure of any single table in the database. Query types in EF Core are designed precisely for such cases, enabling mapping to these non-standard models. By using query types, you can work with data that doesn’t require full CRUD functionality but is essential for displaying or reporting within your application.
Introduced in EF Core 2.1, query types support mapping classes that lack an identity column, like views or database tables without primary keys. They’re read-only, meaning they’re solely for fetching data; you cannot use them to modify or delete records. This makes query types particularly useful for applications needing complex queries or read-only reports, where transactional consistency isn’t a concern. By limiting query types to retrieval operations, EF Core enforces a more secure and performant data access model for certain types of data interactions.
To use query types, you define the mapping between your query and the desired domain class, allowing you to execute database queries without requiring full entity mapping. This flexibility enables developers to harness the power of EF Core’s LINQ to Entities or perform migrations with non-standard data structures. Query types are especially beneficial in applications that use database views extensively, where the structure doesn’t align with standard entities but is still essential for business logic. They demonstrate EF Core’s adaptability, making it a valuable tool for handling both traditional and unique data structures in ASP.NET Core applications.