Creating a ViewModel from two EF Models in ASP.Net MVC5

Question

I have been searching around and really can not find a decent answer on how to build a ViewModel and then fill that with the data from my EF model. The two EF models I want to push into a single ViewModel are:

public class Section
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity), HiddenInput]
    public Int16 ID { get; set; }

    [HiddenInput]
    public Int64? LogoFileID { get; set; }

    [Required, MaxLength(250), Column(TypeName = "varchar"), DisplayName("Route Name")]
    public string RouteName { get; set; }

    [Required, MaxLength(15), Column(TypeName = "varchar")]
    public string Type { get; set; }

    [Required]
    public string Title { get; set; }

    [HiddenInput]
    public string Synopsis { get; set; }

    [ForeignKey("LogoFileID")]
    public virtual File Logo { get; set; }
}

public class File
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Int64 ID { get; set; }

    [Required, MaxLength(60), Column(TypeName = "varchar")]
    public string FileName { get; set; }

    [Required, MaxLength(50), Column(TypeName = "varchar")]
    public string ContentType { get; set; }
}

And I would like to build a ViewModel that looks like:

public class SectionViewMode
{
    public Int16 SectionID { get; set; }

    public bool HasLogo { get; set; } //Set to True if there is a FileID found for the section
    public string Type { get; set; }
    public string Title { get; set; }
    public string Synopsis { get; set; }
}

I would assume it would be best to create a constructor method in the ViewModel so when NEW is called on it the data is filled but what I can not seem to find or figure out is how I go about filling that data.

Shyju · Accepted Answer · 2013-12-25 19:11:04Z

4

This is a tightly coupled approach as your view models are coupled to your domain models. I personally do not prefer this way. I would go for another mapping method which maps from my domain model to viewmodel

If you really want the constructor approach, You may pass the Section object to the constructor and set the property values.

public class SectionViewModel
{
    public SectionViewModel(){}
    public SectionViewModel(Section section)
    {
       //set the property values now.
       Title=section.Title;
       HasLogo=(section.Logo!=null && (section.Logo.ID>0)); 
    }

    public Int16 SectionID { get; set; }    
    public bool HasLogo { get; set; } 
    public string Type { get; set; }
    public string Title { get; set; }
    public string Synopsis { get; set; }
}

and when you want to create your view model object,

Section section=repositary.GetSection(someId);
SecionViewModel vm=new SectionViewModel(section);

edited Dec 25, 2013 at 19:11

answered Dec 25, 2013 at 19:03

Shyju

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9 Comments

CodeCaster Over a year ago

This has little to do with coupling i guess. Why do you not prefer your view models to display properties of domain models? What else is there to show in views?

Shyju Over a year ago

your viewmodel is tightly coupled with domain model(constructor), uless you use an interface. It is ok to have the viewmodel to show properties of domain models. But using the domain model instance in the constructor makes it coupled with domain model. If you want to change your data access layer (with domain models), you need to change your viewmodel code as well

CodeCaster Over a year ago

If you put it like that, I agree. :)

Matthew Verstraete Over a year ago

How would you suggest doing it in a loosely coupled way? Also if there are 100 rows inside my DB how do I fill it will all that data. My understanding of GetSection(someID) would be that it returns only a single row.

Shyju Over a year ago

@MatthewVerstraete GetSection returns a single object of of Section and the mapping method will read the property values of that and set to corresponding properties of the viewmodel instance.

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