How to automatically add data annotations to generated Entities?

Question

I have a bunch of Entity classes generated automatically from from a database connection. I 'd like to add data annotations automatically, for example if a column is of type varchar(100), then i'd like to have the data annotation [StringLength(100)], or if it is not a nullable field, I'd like to have the [Required] annotation. Is this possible?

The only question I found about this is almost 10 years old and the answer at the time is no longer working.

Thanks in advance for any help.

Answer 1

With some more research and some trial and error I managed to do it. Basically it involves editing the T4 template generated by Entity Framework.

After you add the ADO.NET Entity Data Model > EF Designer from data..., you get an EDMX file, and if you expand it on Visual Studio there's a .tt file with the same name as the .edmx file.

On that file, I added under <#=codeStringGenerator.UsingDirectives(inHeader: false)#> the using statement for data annotations:

using System.ComponentModel.DataAnnotations;

Then, a few lines below, after the simpleProperties declaration, in the foreach I added the following:

foreach (var edmProperty in simpleProperties) // <-- Original foreach statement
        {
            if(edmProperty.Nullable == false)
            {
            #>    [Required]
<#
            }
            if(edmProperty.MaxLength != null)
            {
            #>    [StringLength(<#=edmProperty.MaxLength#>)]
<#
            }
//Rest of the auto-generated code...

Saving this file will update the auto-generated .cs files accordingly:

namespace MyNamespace
{
    using System;
    using System.Collections.Generic;

    using System.ComponentModel.DataAnnotations;

    public partial class MyModel
    {
        [Required]
        public int Id { get; set; }
        [Required]
        [StringLength(20)]
        public string MyField { get; set; }
    }
}