Determining If Entity Is Unique In Repository Pattern

Question

Hello,

Using c# and ASP .Net Core 6 I have an N-Tier web application that has implemented a Repository Pattern and Unit of Work.

In this web application, an Admin can create a Hashtag, based on the following model:

 public class Hashtag
 {
     [Key]
     public int Id { get; set; }

     [Required]
     [StringLength(50, ErrorMessage = "Name cannot be longer than 50 characters.")]
     public string Name { get; set; }

     [Required]
     [StringLength(100, ErrorMessage = "Description cannot be longer than 100 characters.")]
     public string Description { get; set; }
 }

In the IHashtagRepository.cs I have added the following Method:

public interface IHashtagRepository : IRepository<Hashtag>
{
    bool CheckIfHashtagExists(string name);
}

In the HashtagRepository.cs I have the following:

public bool CheckIfHashtagExists(string name)
{
    var objFromDb = _db.Find(e => e.Name == name);
    return objFromDb.Any();
}

In the OnPost() Method of the Create.cshtml.cs I would like to ensure that the Hashtag.Name is distinct (not a duplicate).

I though of doing something like this:

var objExists = CheckIfHashtagExists(somenamehere);
if (objExists = True)
{
     Do some stuff
}
else
{
    Do something else
}

I am getting an error on this line in HashtagRepository.cs

var objFromDb = _db.Find(e => e.Name == name);

Compiler Error CS1061 type' does not contain a definition for 'name' and no accessible extension method 'name' accepting a first argument of type 'type' could be found (are you missing a using directive or an assembly reference?).

I am unsure how to correct this error.

Also, I am unsure if there is a more correct way to achieve what I am attempting to do.

My Generic Repository has the following Mathods available in the Interface:

public interface IRepository<T> where T : class
{
    T Get(int id);
    IEnumerable<T> GetAll();
    IEnumerable<T> Find(Expression<Func<T, bool>> expression);
    T GetFirstOrDefault(Expression<Func<T, bool>>? filter = null, string? includeProperties = null);
    void Add(T entity);
    void Remove(int id);
    void Remove(T entity);
    void RemoveRange(IEnumerable<T> entity);
}

Thanks in advance for your help.

It is much appreciated.

Answer 1

@Brian Ashcraft, Welcome to Microsoft Q&A, based on my test, I reproduced your problem.

As the Microsoft Learning DbContext.Find Method described, the method is used to find an entity with the given primary key values.

Therefore, you could not use Find method for non-primary key field.

You could try the following code to check if Hashtag.Name is distinct.

public bool CheckIfHashtagExists(string name)
{
    var objFromDb3 = context.hashtags.Where(m => m.Name == name).Select(m => m.Name);
    var result = objFromDb3.Count() > 0 ? true : false; //->First Method
    var result1= objFromDb3.Any() //->Second Method

    return result;
}

Hope my code could help you.

Best Regards,

Jack

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