@ -21,6 +21,66 @@ public class Book : Entity<Guid>
`Entity<TKey>` class just defines an `Id` property with the given primary **key type**, which is `Guid` in the example above. It can be other types like `string`, `int`, `long` or whatever you need.
`Entity<TKey>` class just defines an `Id` property with the given primary **key type**, which is `Guid` in the example above. It can be other types like `string`, `int`, `long` or whatever you need.
### Entities with GUID Keys
If your entity's Id type is `Guid`, there are some good practices to implement:
* Create a constructor that gets the Id as a parameter and passes to the base class.
* If you don't set a GUID Id, ABP Framework sets it on save, but it is good to have a valid Id on the entity even before saving it to the database.
* If you create an entity with a constructor that takes parameters, also create a `protected` empty constructor. This is used while your database provider reads your entity from the database (on deserialization).
* Don't use the `Guid.NewGuid()` to set the Id! Use [the `IGuidGenerator` service](Guid-Generation.md) while passing the Id from the code that creates the entity. `IGuidGenerator` optimized to generate sequential GUIDs, which is critical for clustered indexes in the relational databases.
An example entity:
````csharp
public class Book : Entity<Guid>
{
public string Name { get; set; }
public float Price { get; set; }
protected Book()
{
}
public Book(Guid id)
: base(id)
{
}
}
````
Example usage in an [application service](Application-Services.md):
````csharp
public class BookAppService : ApplicationService, IBookAppService
public BookAppService(IRepository<Book> bookRepository)
{
_bookRepository = bookRepository;
}
public async Task CreateAsync(CreateBookDto input)
{
await _bookRepository.InsertAsync(
new Book(GuidGenerator.Create())
{
Name = input.Name,
Price = input.Price
}
);
}
}
````
* `BookAppService` injects the default [repository](Repositories.md) for the book entity and uses its `InsertAsync` method to insert a `Book` to the database.
* `GuidGenerator` is type of `IGuidGenerator` which is a property defined in the `ApplicationService` base class. ABP defines such frequently used base properties as pre-injected for you, so you don't need to manually [inject](Dependency-Injection.md) them.
* If you want to follow the DDD best practices, see the *Aggregate Example* section below.
### Entities with Composite Keys
### Entities with Composite Keys
Some entities may need to have **composite keys**. In that case, you can derive your entity from the non-generic `Entity` class. Example:
Some entities may need to have **composite keys**. In that case, you can derive your entity from the non-generic `Entity` class. Example:
Galip Tolga Erdem
7 years ago