How to inject dependency in constructor of model class in ASP.NET MVC 3 with Entity Framework 4.1?

Question

EF requires parameterless constructor but is it possible to override this some how?

public class MyModelClass
{
   ADependency _a;
   public MyModelClass(ADependency a)
   {
      _a = a;
   }
   ...
}

So when the client does a query like:

var myModelClasses = context.MyModelClasses;

each class gets created with the dependent instance injected.

@Joe: yes but I need the dependency to get injected when the model object is created regardless of how it's created. I'll clarify the question. — Christian
– Christian, Commented Aug 19, 2011 at 12:47

Kevin Cloet · Accepted Answer · 2011-08-19 12:47:21Z

2

You could use the empty constructor and use the DependencyResolver and do it IN the constructor.

public class MyModelClass
{
   ADependency _a;
   public MyModelClass()
   {

            _a = DependencyResolver.Current.GetService<_a>();
   }
   ...
}

answered Aug 19, 2011 at 12:47

Kevin Cloet

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3 Comments

Christian Over a year ago

good suggestion, however I'm looking for a way to actually inject the dependency into the constructor.

Eranga Over a year ago

@Christian this solution introduces another set of problems. Now you have hidden dependency with a singleton/static instance. Unit testing and refactoring will be difficult.

Christian Over a year ago

@Eranga, yes I realize this, but it's perhaps better than new up the dependency directly?

Ladislav Mrnka · Accepted Answer · 2011-08-20 12:19:08Z

2

No it is not possible to override. EF have to use parameterless constructor and this behaviour cannot be changed because there is no way to use custom factories. You can either use the solution with service locator pattern mentioned by @Kevin or you can handle ObjectMaterialized event and set the dependency through the property of your entity.

answered Aug 20, 2011 at 12:19

Ladislav Mrnka

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1 Comment

Christian Over a year ago

thanks, I guess Kevin deserves the 'accepted answer' credit then.

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