How to perform add/update of a model object that contains EntitySet
- by David Liddle
I have a similar concept to the SO questions/tags scenario however am trying to decide the best way of implementation.
Tables Questions, QuestionTags and Tags
Questions QuestionTags Tags
--------- ------------ ----
QID QID TID
QName TID TName
When adding/updating a question I have 2 textboxes. The important part is a single textbox that allows users to enter in multiple Tags separated by spaces.
I am using Linq2Sql so the Questions model has an EntitySet of QuestionTags with then link to Tags.
My question is regarding the adding/updating of Questions (part 1), and also how to best show QuestionTags for a Question (part 2).
Part 1
Before performing an add/update, my service layer needs to deal with 3 scenarios before passing to their respective repositories.
Insert Tags that do not already exist
Insert/Update Question
Insert QuestionTags - when updating need to remove existing QuestionTags
Here is my code below however started to get into a bit of a muddle. I've created extension methods on my repositories to get Tags WithNames etc.
public void Add(Question q, string tags)
{
var tagList = tags.Split(new string[] { " " },
StringSplitOptions.RemoveEmptyEntries).ToList();
using (DB.TransactionScope ts = new DB.TransactionScope())
{
var existingTags = TagsRepository.Get()
.WithName(tagList)
.ToList();
var newTags = (from t in tagList
select new Tag
{
TName = t
}).Except(existingTags, new TagsComparer()).ToList();
TagsRepository.Add(newTags);
//need to insert QuestionTags
QuestionsRepository.Add(q);
ts.Complete();
}
}
Part 2
My second question is, when displaying a list of Questions how is it best to show their QuestionTags?
For example, I have an Index view that shows a list of Questions in a table. One of the columns shows an image and when the user hovers over it shows the list of Tags.
My current implementation is to create a custom ViewModel and show a List of QuestionIndexViewModel in the View.
QuestionIndexViewModel
{
Question Question { get; set; }
string Tags { get; set; }
}
However, this seems a bit clumsy and quite a few DB calls.
public ViewResult Index()
{
var model= new List<QuestionIndexViewModel>();
//make a call to get a list of questions
//foreach question make a call to get their QuestionTags,
//to be able to get their Tag names and then join them
//to form a single string.
return View(model);
}
Also, just for test purposes using SQL Profiler, I decided to iterate through the QuestionTags entity set of a Question in my ViewModel however nothing was picked up in Profiler? What would be the reason for this?
