Question

I have 3 tables with the following columns in my database:
tool: toolid, tool_name
facet: facetid, facet_name
tool_facet: tf_id, tf_toolid, tf_facetid

The third table contains a list of tools and their facets:
e.g.
1 tid2 fid3
2 tid2 fid4
3 tid3 fid2

where tid2 and fid3 are ids for tools and facets respectively.

In another combo box the user has chosen a specific tool. I want to now display the facets that apply to this tool in another combo box.

Any suggestions?

Thanks.

Answer 1

Surely you simply need to repopulate the second combo box’s items when the user makes a selection in the first?

You likely don’t want to requery the database each time the user makes a selection and so instead will want to hold a structure in memory of all valid facets keyed on toolid.

EDIT some further detail based on Dave’s comment:

Assuming that you already have some code setup to query the database, you want to execute a query (or queries) that give you back the relevant data to hold in a cache and do this as part of your app’s initialisation after connecting to the database. You could create two dictionaries to hold the tool and facet data. For example:

Dictionary<int, string> _tools = new Dictionary<int, string>();
Dictionary<int, string> _facets = new Dictionary<int, string>();

and then a third structure that basically holds the data in tool_facet:

Dictionary<int, List<int>> _tool_facets = new Dictionary<int, List<int>>();

these basically give you an in-memory copy of the tables that you can very quickly enumerate to populate combo boxes. You’ll want to populate the combo boxes with something that holds the ID and a description, something like this will do:

class ComboBoxIntItem
{
  private readonly int _id;
  private readonly string _name;
  public ComboBoxIntItem(int id, string name)
  {
    _id = id;
    _name = name;
  }
  public override string ToString()
  {
    return _name;
  }
  public int GetId()
  {
    return _id;
  }
}

I’m assuming here that you need to know the tool and facet IDs that the user has selected. If you only care about the names then you could just use a single structure like this:

Dictionary<string, List<string>> _tool_facets = new Dictionary<string, List<string>>();