元数据类与asp.net MVC中的ViewModel是否相同？

Question

I'm a little confused about this one. I read about metadata classes in this article on MSDN.

It says that the reason for creating metadata is not to mess with the auto generated models by EF.

So this is a model generated by EF:

namespace Blog.Models
{
    using System;
    using System.Collections.Generic;

    public partial class Article
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public Article()
        {
            this.ArticleTags = new HashSet<ArticleTag>();
            this.Comments = new HashSet<Comment>();
        }

        public int ArticleID { get; set; }
        public string PostTitle { get; set; }
        public string PostContent { get; set; }
        public string PostLinkText { get; set; }
        public Nullable<System.DateTime> PostDateTime { get; set; }
        public Nullable<int> PostAuthorID { get; set; }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<ArticleTag> ArticleTags { get; set; }
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<Comment> Comments { get; set; }
        public virtual Admin Admin { get; set; }
    }
}

and this is metadata class for Article model:

public class ArticleMetadata
    {
        [Display(Name = "Post Title")]
        public string PostTitle { get; set; }

        [Display(Name = "Content")]
        public string PostContent { get; set; }

        [Display(Name = "Link Text")]
        public string PostLinkText { get; set; }

        [Display(Name = "Post Date and Time")]
        public DateTime? PostDateTime { get; set; }

        [Display(Name = "Post Author")]
        public int? PostAuthorID { get; set; }
    }

linked to model class using PartialClasses.cs:

[MetadataType(typeof(ArticleMetadata))]
public partial class Article
{
}

Is the metadata class the same as a ViewModel??

If so, how are these different and which one should be used in my case?

Answer 1

No, they aren't the same.

Metadata classes allow you to define/add restraints to your class members.

View models are usually used to make it easier to use your model in a view. Such as having lists of SelectListItems for dropdowns, having properties to accept form post values, etc.

The two are usually used in conjunction, you add validation in your metadata class, and enforce it through the view model.

In your specific case, it seems all you need is a metadata class.

Answer 2

class ArticleMetadata is a helper class for class Article , needed because you can't otherwise add those Annotation attributes to specific properties.
Together they form the Model part of MVC.

Note that the partial class can't help with the properties because it can't redefine them. It is used here only to link up the MetaData class.

For very simple operations (CRUD pages) you can use the Model directly. In all other case, create a ViewModel for each View. The Article Model will probably be used by an EditArticleViewModel.

In general you should create ViewModels to support Views, not one for each Model. One ViewModel could be composed of data from several Model classes.