✅ Help understanding validation magic in ASPNET WebAPI

C#
[ApiController]
[Route("[controller]")]
public class ProjectsController : ControllerBase
{

C#
[ApiController]
[Route("[controller]")]
public class ProjectsController : ControllerBase
{

using Microsoft.AspNetCore.Mvc;

using Microsoft.AspNetCore.Mvc;

C#
    public class ProjectCreateBody: IValidatableObject
    {
        [Required]
        public string Name { get; set; }
        
        [Required]
        public string[] Query { get; set; }
        
        [Required]
        public string[] Urls { get; set; }

        public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        {
            
            var db = validationContext.GetService<Database>();
            
            if (db.Projects.Exists(p => p.Name == Name))
            {
                yield return new ValidationResult("Project already exists", [nameof(Name)]);
            }
        }
    }
    
    [HttpPost(Name = "CreateProject")]
    [ProducesResponseType(StatusCodes.Status201Created, Type=typeof(Project))]
    [ProducesResponseType(StatusCodes.Status400BadRequest, Type = typeof(ValidationProblemDetails))]
    public IActionResult Post([FromBody] ProjectCreateBody project)
    {
        return Ok(project);
    }

C#
    public class ProjectCreateBody: IValidatableObject
    {
        [Required]
        public string Name { get; set; }
        
        [Required]
        public string[] Query { get; set; }
        
        [Required]
        public string[] Urls { get; set; }

        public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
        {
            
            var db = validationContext.GetService<Database>();
            
            if (db.Projects.Exists(p => p.Name == Name))
            {
                yield return new ValidationResult("Project already exists", [nameof(Name)]);
            }
        }
    }
    
    [HttpPost(Name = "CreateProject")]
    [ProducesResponseType(StatusCodes.Status201Created, Type=typeof(Project))]
    [ProducesResponseType(StatusCodes.Status400BadRequest, Type = typeof(ValidationProblemDetails))]
    public IActionResult Post([FromBody] ProjectCreateBody project)
    {
        return Ok(project);
    }