Question

I am trying here to make a few left joins into a linq query but I’d say I rather have no idea how to materialize this idea.

Basically here is the 3 database structures I want to play with.

<tags>
id | name

<events_tags>
tag_id | event_id

<events>
id | name | some-other-fields

so for each events there is a one-to-many relation with tags, an event can then have one or more tags.

I’d like to know how to search an event based on a tag or how can I, based from an event id know the associated tags ?

Answer 1

To search event by tag, I think you can write something like:

var tagsIds = from t in DataContext.Tags
              where t.Name == "sometag"
              select t.id;

var eventsByTag = from et in DataContext.EventTags
                  where tagsIds.Contains(et.tag_id)
                  select et.Event;

To get the tags for an event:

var tagsByEvent = from et in myEvent.EventTags
                  select et.Tag;

For the latter, for convenience, you can put it in a property of Events:

public List<Tag> Tags
{
   get
   {
      List<Tag> tags = (from et in this.EventTags
                        select et.Tag).ToList();
      return tags;
   }
}

And just refer to myEvent.Tags where you need them.