We built a mechanism that on server request automatically retrieves the entities list from the DB, and maps them to ViewModels. We can't figure out how to support clearing View Models that are built from multiple DB entities when an update was made to some relevant DB entity.
This is how we've built our Cache:
We have a mapping between the key (the DB entity name) and the list of values it holds (View models).
This is how we handle entities invalidate:
On EF's Context Save method, we clear the Cache values by the saved entity's name (when it has been changed).
For most entities, all the Cache values are mapped to a single entity.
For some entities however, the Cache values depend on several other entities (which are either direct or indirect navigation properties of the entity).
For instance:
We have an EducationPlace Entity.
Its Cache key is "EducationPlace". Its values are a list of EducationPlaceViewModel.
EducationPlace entity has an Address property, and the Address entity, has a City property.
City's name is used in the EducationPlaceViewModel.
Now we want, that when the City entity is being updated, the Cache's EducationPlaceViewModel list will be cleared.
What we are looking for, is a way to update a cache entry, when an entity that the cache entry's View Model depends on is being updated.
The two solutions we've considered are:
- Use reflection to find which entries should be cleared (by following the navigation properties). This will create many unnecessary dependencies, which will result in many redundant cache clears. For instance, EducationPlace has many navigation properties that are not being used by its View Model, hence should not trigger a Cache clear.
- Use a custom Attribute that will decorate each relevant entity, and will hold its list of entities that its View Model depends on. This way we will easily get the entities that should be cleared when an entity is being saved at the Save method. This way requires A LOT of maintenance. It requires for each new entity which its View Model depends on other entities for the developer to remember to use it on the new entity, and to update that entity when its View Model depends on new entities.
This is how we clear the View Models.
This method is invoked from the Context's Save method:
What this method basically does is:
- It gets all the DB entities from the DAL layer
- For each entity name, it:
a. Skips none-relevant entities
b. if the entity name exists as a Cache key - Clear its data