Question 85860 in ASP.NET Question posted in
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How can i add a base constructor to the database connection class? – Asp.net

I use EfFeatureDal class as a database connection class and i use constructor for this connection. But when i need to call this class from FeatureList i cant add these connection constructor’s parameters thats why i need base constructor on EfFeatureDal but i cant add it?

public class FeatureList:ViewComponent
{

    FeatureManager featureManager = new FeatureManager(new EfFeatureDal());

    public IViewComponentResult Invoke() 
    {
        return View();
    }
}

public class EfFeatureDal : GenericRepository<Feature>, IFeatureDal
{
    public EfFeatureDal(Context1 _db) : base(_db)
    {
    }

    public EfFeatureDal() { }

}

I got this error on base constructor:

Error CS7036 There is no argument given that corresponds to the
required parameter ‘_db’ of
‘GenericRepository.GenericRepository(Context1)’

public class FeatureList:ViewComponent
{

    FeatureManager featureManager = new FeatureManager(new EfFeatureDal());

    public IViewComponentResult Invoke() 
    {
        return View();
    }
}

I got this error when i delete base constructor on new FeatureManager(new EfFeatureDal()):

Error CS7036 There is no argument given that corresponds to the
required parameter ‘_db’ of ‘EfFeatureDal.EfFeatureDal(Context1)’

Tags:

2

Answers


  1. 0

    The mistake that you made is you are trying to instantiate EfFeatureDal manually and you got stuck in the trap, actually you need to know about DI(Dependency Injection) Concept and use a IoC container to instantiate and inject EfFeatureDal object in your derived objects.
    you can see a sample here

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  2. 0

    When i need to call this class from FeatureList i cant add these
    connection constructor’s parameters thats why i need base constructor
    on EfFeatureDal but i cant add it?

    Well, It would be perfect it if you would have been shared FeatureManager details. However, If your EfFeatureDal class has implicitly defined a constructor within it as following:

     public EfFeatureDal(ApplicationDbContext context) : base(context) { }

    As it has constructor dependency, you must have to pass the constructor if you would like to create its instance somewhere. But this is not the common practice we do everyday.

    What you can do is, if you need to access EfFeatureDal methods or anything you have defined there, you can call it in derived class by injecting its interface within derived class constructor. Have a look in following example:

    public class FeatureList : ViewComponent
    {

        private readonly IEfFeatureDal _efFeatureDal;

        public FeatureList(IEfFeatureDal featureDal)
        {

            _efFeatureDal = featureDal;
        }

        public IViewComponentResult Invoke()
        {
           _efFeatureDal... // Anything you want to call from your repository
            return View();
        }
    }

    Output:

    enter image description here

    Alternatively:

    If you have defined FeatureManager as following:

    public class FeatureManager
    {
        public FeatureManager(EfFeatureDal featureDal) { }
    }

    In that scenario, if you would like to call EfFeatureDal in your FeatureList derived class you have to pass DbContext as its constructor parameter. You can do that in following manner:

    public class FeatureList : ViewComponent
    {
        private readonly ApplicationDbContext _context;
        public FeatureList(ApplicationDbContext dbContext)
        {

           
            _context = dbContext;
        }

        public IViewComponentResult Invoke()
        {

            FeatureManager feature = new FeatureManager(new EfFeatureDal(_context));
            return View();
        }
    }

    Note: We are passing _context to EfFeatureDal because it has constructor dependency that is public EfFeatureDal(ApplicationDbContext context) : base(context) { }. Thus, Always keep in mind base-class constructor should be called when creating instances of the derived class. I would recommend you to check our official document for more details.

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