Entity Framework : implemeting very simple association scenario

Question

I want to implement the below mentioned problem in Entity Framework.

I have 2 tables( below are their simplified versions)

items table

itemId,itemName

tags table

tagId,tagName

• my logic is, an item can have more than one tag and a tag can have more than one item related to it, so I have added many to many relation (please correct me here, if I am wrong)

• I have created model (edmx file) and database from it.

• I have written code for adding data to my sample tables, and its working fine. Below is sample data

  itemId  itemName  ---items table
     1   |  fish
     2   |  cell phone
  
  
  tagId    tagName ------tags table
     1   |  eatable
     2   |  electronics
     3   |  non veg
  

I need to know how to write these 3 queries

1. add relation between tag and item e.g. add tags "eatables", "nonveg" to item "fish"
2. get all tags related to an item (eg: fish)
3. get all tags not related to an item (eg: fish)

Answer 1

If your association is in place with normal naming (an EDMX diagram in your question would help) ...

Q 1.

Tag tag = ...  // probably load from database or create if necessary
Item item = ...
item.Tags.Add(tag);

Q 2.

var tags = item.Tags;

Q 3.a All tags not related to ANY item

var unrelatedTags = context.Tags.Where(tag => tag.Items.Count() > 0);

Q 3.b All tags not related to a specific item

var unrelatedTags = context.Tags.Except(item.Tags);