Entity Name reflector

Question

Hi All

 

I have a Blog entity with a Blog_ID field. Is it possible for me to do some reflector to get the Blog_ID and return it as string?

 

It is because I am building a selectlist but don't want to hard code like this.

new SelectList(blog,"blog_ID","blog_Description");

 

I want to make it strong-typed, is it possible?

 

Regards

Alex

Answer 1

Yes, it's possible.

 

In my opinion, the best way is to check EntityKeyMembers array of the EntityKey property of the Blog entity. You can then get a name list if your key fields.

 

On the other hand you can use reflection on the Blog entity and iterate through all properties to see their CustomAttributes and check if it's of type EdmScalarPropertyAttribute and if so, see if EntityKeyProperty is true. For example, to get a list of all key properties:

 

 

foreach (PropertyInfo prop in typeof(Blog).GetProperties())

{

object[] attrs = prop.GetCustomAttributes(false);

foreach (object obj in attrs)

{

if (obj.GetType() == typeof(EdmScalarPropertyAttribute))

{

EdmScalarPropertyAttribute attr = (EdmScalarPropertyAttribute)obj;

if (attr.EntityKeyProperty)

keyList.Add(prop.Name);

}

}

}

 

 

 

Hope it helps

Answer 2

Instead of using strings or reflection you could consider lambda expressions.

You can create a generic SelectList with this constructor:

Code Snippet

SelectList(T entity, Expression<Func<T,object>> field1, Expression<Func<T,object>> field2)

 

Then you can use it like this with strong typing:

Code Snippet

new SelectList(blog, b=>blog_ID, b=>blog_Description);

 

You don't even need to create a generic class if you don't want to and mine the corresponding strings from the expression trees above:

Code Snippet

static SelectList CreateList<T>(T entity, Expression<Func<T,object>> field1, Expression<Func<T,object>> field2)

{

    string f1name = (field1.Body as MemberExpression).Member.Name;
    string f2name = (field2.Body as MemberExpression).Member.Name;

    return new SelectList(entity, f1name, f2name);
}

 

SelectList.Create(blog, b=>blog_ID, b=>blog_Description);

Although this latter aproach will only throw a runtime exception if you use different expressions than the intended simple field access.

Answer 3

Excellent Solution!!! Thanks.

 

However, My selectlist's original data type is a List and the code is as follows :-

 

ViewData["Blog_TypeList"] = WebUtility.CreateList (blog_TypeList.OrderBy(c => c.Seq), c => c.First().Blog_Type_ID, c => c.First().Description);

 

Could I remove the First() from the code?

       

Answer 4

You can change the "T entity" parameter to "IEnumerable<T> entities". The compiler will still deduce the generic parameter for the function.

Answer 5

Thanks. Cool. It works.

 

Besides, just curious, for this solution:-

 

Code Snippet

SelectList(T entity, Expression<Func<T,object>> field1, Expression<Func<T,object>> field2)

 

Then you can use it like this with strong typing:

Code Snippet

new SelectList(blog, b=>blog_ID, b=>blog_Description);

 

 

Where do I put the constructor, modify the source code?

 

 

Answer 6

        public static string[] GetIdField<TEntity>() where TEntity : EntityObject
        {
            IEnumerable<string> ids = from p in typeof(TEntity).GetProperties()
                                      where (from a in p.GetCustomAttributes(false)
                                             where a is EdmScalarPropertyAttribute &&
                                             ((EdmScalarPropertyAttribute)a).EntityKeyProperty
                                             select true).FirstOrDefault()
                                      select p.Name;

            return ids.ToArray();
        }

---

Shimmy