Repodb: Help: How to dynamically add non db value to object property.

[Kodestuen]

Hey,

I have a small challange that I guess/hope can be implemented in a low level fashion.

In my base model I have a UserGuid that is persisted in the DB, but I will also have a "virtual" property UserName that is added from a Dictionary (Cached from the db) after the object has been loaded.

How can I hijack this so I can enrich my model just after Db load?

Best Christian,

[mikependon]

There is no class handler in RepoDB, I am thinking of it before. But I guess it is a bit high-level and edge case which would only happen 1% or 0.5% of all cases. But, there is a feature called Property Handler in which you can hook up (DURING the object is being transformed), (not AFTER the object has been loaded).

I would assume you have the models below (or almost identical).

public class YourBaseModel
{
    public Guid UserGuid { get; set; }
    [PropertyHandler(typeof(UserNamePropertyHandler))]
    public virtual string UserName {get; set; }
}

public class YourEntityModel : YourBaseModel
{
    public string Property1 { get; set; }
    ...
} 

You should create the Property Handler like below.

public class UserNamePropertyHandler : IPropertyHandler<string, string>
{
    public string Get(string input, ClassProperty property)
    {
        // This event is being triggered before the property is set back to the model
        // --->>>> Get the cache data here
    }

    public string Set(string input, ClassProperty property)
    {
        // This event is being triggered before the property is saved to the DB
    }
}

If you do not like the attribute PropertyHandler, you can also do map it via FluentMapper like below.

FluentMapper.Entity<YourEntityModel>().PropertyHandler<UserNamePropertyHandler >(e => e.UserName);

Hope this helps!

[Kodestuen]

Okay kind a work, but it seems like I can only work on one property.

Situation:

Property A is mapped in DB
Property B is only in model.

As I see this, I can only manipulate property A based on field A (value in Db).
But not set/manipulate property B based on the value of A?

Is that correct?

[mikependon]

Yes, you are really needing a class handler in which we did not implemented. Also, I just realized that the property handler may not be triggered as it is not mapped to any column of your DB.

Are you blocked here? I am just a bit pushy on the reco above, but upon further understanding your case, IMHO, I would say that you just simply customize the 'getter' of your property in the Model and get the value directly from cache or from any other Model properties.

[mikependon]

Maybe you do not need an event of the 'After Model Load', but maybe a trick below would do?

public class YourBaseModel
{
    public Guid UserGuid { get; set; }

    public virtual string UserName => GetUserNameValue();

    private string GetUserNameValue()
    {
        var value = "Get From Cache";
        return $"User-{UserGuid}-{value}";
    }
}

public class YourEntityModel : YourBaseModel
{
    public string Property1 { get; set; }
    ...
} 

[mikependon]

Hey @Kodestuen - how is the status on your side here?

[Kodestuen]

Hi @mikependon,

I would like to keep my model as clean as possible and my challenge is that I fetch the UserName from the DB itself (cached)

private string GetUserNameValue(Dictionary<Guid, string> users)
    {
        //var value = "Get From Cache"; //Should not know this internally
        return users[UserGuid];
    }

I have tried to solve it in my (repository handler).

But need to surround this on all functions before they return. All, Select, Insert etc.

```
public IEnumerable Enrich(List list)
{
list.ForEach(f => f.UserName = f.CreatedByUserId.GetUserName(DbHandler)); //GetUserName is an extension method
return list.AsEnumerable();
}

So yes a ClassHandler :-)

[ClassHandler(typeof(SomeClassHandler))]
public class YourBaseModel
{
public Guid UserGuid { get; set; } // in DB

public string UserName {get; set; } // SomeClassHandler will set this value based on UserGuid

}

public class SomeClassHandler: IClassHandler
{
public YourBaseModel Get(YourBaseModel object)
{
// Manipulate/transform as you like....
return object;
}

}
```

[mikependon]

To be honest, it is not that difficult to introduce this. I am thinking to include this on the next beta release. But I am just afraid that my upcoming release is now bloating up. You can see the upcoming release here. A lot of requests from F# community and some other additional requests from C# community has also been introduce, including this? :)

In anyway, let me think of it and will let you know once I included it on the next beta release. This is a good reconsideration.

[Kodestuen]

@mikependon you are the best. I think this project is some of the coolest work I ever have seen. THANK you :-)

[mikependon]

Thanks! Just leave this one open, I will make a comment here moving forward. For now, please do a manual work around on your end. Cheers!

[mikependon]

@Kodestuen - would you be able to check the class handler support on the latest release (RepoDB v1.12.0-beta1)?

[mikependon]

Closing this ticket now as the Class Handler feature is introduced to support this. Please do let us know if you have any further questions.