CODEWITHSUNDEEP
asp.net-mvcselectlistitem
Scott Althaus
Scott Althaus

Reputation: 85

Populating a SelectList with Parent/Child Tables

I am trying to populate an Html.DropDownList in MVC. The problem I'm having is that I have a child table called "ODSessionTopics" that has a foreign key (ID) to the "ODSessionType" table which contain the headers for the topics. Here are my models: 

public class ODSessionTopic
{
    public int ID { get; set; }
    public string Description { get; set; }

    // foreign key
    public int ODSessionTypeID { get; set; }

    // navigation property
    public virtual ODSessionType ODSessionType { get; set; }               
}

public class ODSessionType
{
    public int ODSessionTypeID { get; set; }

    public string Description { get; set; }

    // navigation property
    public virtual ICollection<ODSessionTopic> ODSessionTopics { get; set; } 
}

I use the following code to populate the ViewBag:

ViewBag.ODSessionTopicID = new SelectList(db.ODSessionTopics, "ID", "Description", "ODSessionTypeID", oDSession.ODSessionTopicID);

Here is the OD Session Topic data:

    ID           Description            ODSessionTypeID
    ---------------------------------------------------
    1            Internal Marketing     1
    2            Team Development       1
    3            Department Retreat     2
    4            Community Service      2

Here is the OD Session Type data:

    ODSessionTypeID           Description
    ------------------------------------- 
    1                         Plan     
    2                         Action

These are my results:

    1 
       Internal Marketing
       Team Development
    2
       Department Retreat
       Community Services

Here are the results I am trying to achieve:

    Plans
       Internal Marketing
       Team Development
    Actions
       Department Retreat
       Community Services

The view code is

@Html.DropDownList("ODSessionTopicID", null, "-- Session Type --", htmlAttributes: new { @class = "form-control" })

Basically, it's grabbing the ODSessionTypeID foreign key in the ODSessionTopic table and grouping by that value. What I need it to do is grab the description from the ODSessionType table. Is this possible? Both the topics and the types are editable and have CRUD logic attached to them which is how I arrived to this design in the first place.

Upvotes: 2

Views: 2483

Answers (1)

user3559349
user3559349

Reputation:

You can use a linq .Join() and project the results to an anonymous object. Assuming var topics = db.ODSessionTopics; and var types = db.ODSessionTypes; then the query would be

var query = from topic in topics
            join type in types on topic.ODSessionTypeID equals type.ODSessionTypeID
            select new { Group = type.Description, ID = topic.ID, Description = topic.Description };

which will output

{ Group: "Plan", ID: 1, Description: "Internal Marketing" }
{ Group: "Plan", ID: 2, Description: "Team Development" }
{ Group: "Action", ID: 3, Description: "Department Retreat" }
{ Group: "Action", ID: 4, Description: "Community Services" }

and to create the SelectList

ViewBag.ODSessionTopicID = new SelectList(query, "ID", "Description", "Group", oDSession.ODSessionTopicID)

Side note: Recommend you use the strongly typed html helpers to generate your dropdownlist. Your ViewBag property should not be the same name as the property your binding to. Instead it should be (say)

ViewBag.TopicList = new SelectList(query, "ID", "Description", "Group", null)

and in the view

@Html.DropDownListFor(m => m.ODSessionTopicID, (SelectList)ViewBag.TopicList, "-- Session Type --", new { @class = "form-control" })

Upvotes: 1

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