ORMers,how are you going to deal with this in the ORM style?

Question

We are modifying our post on stackoverflow.

And we only changed the tags part,removed tag1,tag2 and added tag3,tag4.

After pressing the Post Your Question button,these things should be done:

1. reduced the count column for tag1,tag2 by 1
2. delete the relation between the post and tag1,tag2
3. if tag3,tag4 already exists,increase the count column of the two by 1;otherwise,insert them to the tags table with count value 1
4. add the relation between the post and tag3,tag4

Let's take a deep breath and that's all!

I want to see which ORM can approach this most easily/performant no matter it's written in PHP/Java/C/.Net or any language else,because the ideas are similar across languages!

Answer 1

In DataObjects.Net it will look like this. There is now any mapping files because database schema is automatically generated by ORM, including auxiliary table for question-tag relation.

Tag class:

[HierachyRoot]
public class Tag : Entity
{
  [Field, Key]
  public int Id { get; private set; }

  [Field(Length = 100, Indexed = true)]
  public string Name { get; private set; }

  [Field]
  public int QuestionsCount { get; set; }

  public Tag(string name) 
  {
    Name = name;
  }
}

Question class:

[HierachyRoot]
public class Question : Entity
{
  [Field, Key]
  public int Id { get; private set; }

  [Field]
  public EntitySet<Tag> Tags { get; private set; }

  // Business methods (can be placed in separate service class)

  public void AddTag(string name)
  {
    var tag = Query.All<Tag>().SingleOrDefault(t => t.Name == name);
    if (tag==null)
      tag = new Tag(name) { QuestionsCount = 1 }
    else
      tag.QuestionsCount++;
    Tags.Add(tag);
  }

  public void RemoveTag(string name)
  {
    var tag = Query.All<Tag>.Single(t => t.Name == name);
    tag.QuestionsCount--;
    Tags.Remove(tag);
  }
}

Application code:

using (Session.Open())
using (var transactionScope = Transaction.Open())
{
  var question = Query.Single<Question>(questionId);

  question.RemoveTag("tag1");
  question.RemoveTag("tag2");

  question.AddTag("tag3");
  question.AddTag("tag4");

  transactionScope.Complete();
}