ABP Feature system is used to **enable**, **disable** or **change the behavior** of the application features **on runtime**.
The runtime value for a feature can simply be a `boolean`, like enabled (`true`) or disabled (`false`). However, you can store **any kind** of runtime value for feature.
The runtime value for a feature is generally a `boolean` value, like `true` (enabled) or `false` (disabled). However, you can get/set **any kind** of value for feature.
Feature system was originally designed to control the tenant features in a **multi-tenant** application. However, it is **extensible** and capable of determining features by any condition.
Feature system was originally designed to control the tenant features in a **multi-tenant** application. However, it is **extensible** and capable of determining the features by any condition.
> The feature system is implemented with the [Volo.Abp.Features](https://www.nuget.org/packages/Volo.Abp.Features) NuGet package. Most of the times you don't need to manually [install it](https://abp.io/package-detail/Volo.Abp.Features) since it comes pre-installed with the [application startup template](Startup-Templates/Application.md).
## Checking for the Features
Before starting to explain how to define features, let's see how to check a feature in your application code.
Before explaining to define features, let's see how to check a feature value in your application code.
### RequiresFeature Attribute
`[RequiresFeature]` attribute (defined in the `Volo.Abp.Features` namespace) is used to declaratively check if a feature is enabled or not. It is a useful shortcut for the `boolean` features.
`[RequiresFeature]` attribute (defined in the `Volo.Abp.Features` namespace) is used to declaratively check if a feature is `true` (enabled) or not. It is a useful shortcut for the `boolean` features.
**Example: Check if the "PDF Reporting" feature enabled**
@ -42,10 +42,10 @@ ABP Framework uses the interception system to make the `[RequiresFeature]` attri
However, there are **some rules should be followed** in order to make it working;
* If you are **not injecting** the service over an interface (like `IMyService`), then the methods of the service must be `virtual` (otherwise, [dynamic proxy / interception](Dynamic-Proxying-Interceptors.md) system can not work).
* If you are **not injecting** the service over an interface (like `IMyService`), then the methods of the service must be `virtual`. Otherwise, [dynamic proxy / interception](Dynamic-Proxying-Interceptors.md) system can not work.
* Only `async` methods (methods returning a `Task` or `Task<T>`) are intercepted.
> There is an exception for the controllers and razor pages. They don't require the following rules since ABP Framework uses action/page filters to implement the feature checking in this case.
> There is an exception for the **controller and razor page methods**. They **don't require** the following the rules above, since ABP Framework uses the action/page filters to implement the feature checking in this case.
### IFeatureChecker Service
@ -125,7 +125,7 @@ public class ProductController : AbpController
}
```
In this way, you can create numeric limits in your SaaS application depending on the current user or tenant.
This example uses a numeric value as a feature limit product counts for a user/tenant in a SaaS application.
Instead of manually converting the value to `int`, you can use the generic overload of the `GetAsync` method:
@ -135,4 +135,27 @@ var maxProductCountLimit = await _featureChecker.GetAsync<int>("MyApp.MaxProduct
#### Extension Methods
There are some useful extension methods for the `IFeatureChecker` interface;
* `Task<T> GetAsync<T>(string name, T defaultValue = default)`: Used to get a value of a feature with the given type `T`. Allows to specify a `defaultValue` that is returned when the feature value is `null`.
* `CheckEnabledAsync(string name)`: Checks if given feature is enabled. Throws an `AbpAuthorizationException` if the feature was not `true` (enabled).
Halil İbrahim Kalkan
5 years ago