Check if item exists

Question

I have a service to Insert TagName , I dont want to insert duplicate tags I used this :

 public void Insert(string tagName)
 {
 tagName = tagName.Trim();
 if (IsExists(tagName))
 throw new ArgumentException("tagName is Exists");
 Tag model = new Tag { Name=tagName};
 _uow.MarkAsAdded(model);
 }
 public bool IsExists(string tagName)
 {
 return _tags.Any(row=>row.Name==tagName.Trim());
 }

and another way is change If statement like below :

 public void Insert(string tagName)
 {
 tagName = tagName.Trim();
 if (!IsExists(tagName))
 {
 Tag model = new Tag { Name = tagName };
 _uow.MarkAsAdded(model);
 }
 }

I decided to use second one because I add another method Like this :

 public void Insert(string[] tags)
 {
 foreach (var item in tags)
 {
 Insert(item);
 }
 }

If I throw exception , Insert(string[] tags) will not completed .

Updated:

 private readonly IDbSet<Tag> _tags;
 #region ctor
 public TagService(IUnitOfWork uow)
 {
 _uow = uow;
 _tags = _uow.Set<Tag>();
 }
 #endregion

Answer 1

You make this harder then it needs to be.

Since IDbSet implements the IEnumerable<TEntity> interface

 public interface IDbSet<TEntity> 
 : IQueryable<TEntity>, IEnumerable<TEntity>, IQueryable, IEnumerable

you can simply use the Contains extension optionally with your own comparer that can implement such things as Trim etc.

• work question: I used Trim() beacse I don't want to save Tag name with spaces around it , Like this C# or ` MVC `
• t3chb0t: @workquestion sure, I'm not saying that it's wrong just that you could put it in the comparer and call it again just before adding a new tag.
• RobH: @t3chb0t - I don't think a comparer is the right choice for encoding important domain rules. Here, the OP is saying Tagname must never have surrounding whitespace. I think Trimming incoming values is a better choice (but that's up for debate!)
• t3chb0t: @RobH true, I always say there should be multiple sting types for this, case-insensitive and trimmed ones becasue this two are causing too many bugs.
• RobH: @t3chb0t - I know what you mean... Especially with SQL's handling of equality see here. It's easy to have stuff in the DB returning true and stuff in C# returning false if you don't trim the strings somewhere.