EF6: How do I search for an item in a List?

Question

I have a simple ASP.Net MVC app with Entity Framework 6.

I have two tables: a "Contacts" list (with names, addresses and phone#s) and a second table that records zero or more "Notes" history records for each contact:

Models/Contact.cs:

   public class Contact
    {
        [Key]
        [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
        public int ContactId { get; set; }
        public string Name { get; set; }
        public string EMail { get; set; }
        public string Phone1 { get; set; }
        ...
        public virtual List<Note> Notes { get; set; }
    }

Models/Note.cs:

public class Note
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int NoteId { get; set; }
    public string Text { get; set; }
    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime? Date { get; set; }
    [ForeignKey("Contact")]
    public int ContactId { get; set; }
    public virtual Contact Contact { get; set; }
}

I did an "Add Controller" in Visual Studio, which auto-generated "ContactsController.cs" and Views for "Index.cshtml", "Details.cshtml", "Edit.cshtml" and "Delete.cshtml". All the auto-generated code looks good, and runs fine. But it didn't show any "Notes".

I was able to display the "notes" and add links to Edit or Delete a note by adding the following to "Details.cshtml" and "Edit.cshtml":

Views/Contacts/Edit.cshtml:

@model ContactsApp.Models.Contact
...
<h4>Notes</h4>
<table class="table">
    <tr>
        <th>Date</th>
        <th>Note</th>
        <th>&nbsp;</th>
    </tr>

    @for (int i = 0; i < Model.Notes.Count(); i++)
    {
        <tr>
            <td>@Html.DisplayFor(model => model.Notes[i].Date)</td>
            <td>@Html.DisplayFor(model => model.Notes[i].Text)</td>
            <td>
                @Html.ActionLink("Edit Note", "EditNote", new { noteId = Model.Notes[i].NoteId }) |
                @Html.ActionLink("Delete Note", "DeleteNote", new { noteId = Model.Notes[i].NoteId })
            </td>
        </tr>
    }
</table>

I've also created an "EditNote.cshtml" view ... but I haven't been able to figure out how to call it from ContactsController:

Controllers/ContactsController.cs:

   // GET: Contacts/EditNote?noteId=3
    public async Task<ActionResult> EditNote(int? noteId)
    {
        if (noteId == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        Note note = await db.Contacts.Where(c => c.Notes.noteId == noteId);
        if (note == null)
        {
            return HttpNotFound();
        }
        return View(note);
    }

Q: What is the correct ASP.Net MV syntax to fetch the "Note" and pass it down to the "EditNote" view?

score 2 · Answer 1 · answered Nov 18 '19 at 07:58

2

Your code shouldn't normally compile due to the following line:

Note note = await db.Contacts.Where(c => c.Notes.noteId == noteId);

The type of the expression on the right is IEnumerable<Contact>, whereas the type of the variable you assign it is Note. This should change to the following:

Note note = await db.Notes.FirstOrDefaultAsync(note => note.NodeId == noteId);

Btw: Where is a synchronous call, so no need for using the await keyword.

answered Nov 18 '19 at 07:58

Christos

53,228
8
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It *didn't* compile. My question was how to get the syntax for querying the right "Note" with respect to "Contacts". You and Athanasios Kataras pointed me in the right direction: I shouldn't be dealing with "Contacts" at all. If I want a "Note" ... I should simply query the "Notes" table. I did - and it worked :) Thank you! – FoggyDay Nov 18 '19 at 08:19

score 1 · Accepted Answer · answered Nov 18 '19 at 07:59

1

You are returning a Contact.

You should be querying notes and using FirstOrDefault.

db.Notes.Where(n=> n.NoteId =id).FirstOrDefault();

If you want to select from contacts by id and note id for better efficiency, try Using LINQ, select list of objects inside another list of objects

answered Nov 18 '19 at 07:59

Athanasios Kataras

25,191
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Perfect - thank you. My mistake was thinking that I needed to query "Contacts" to find the right "note". I didn't even expose "Notes" in my DBContext class - only "Contacts". And things seemed to work. For awhile, until this problem. So I added Notes to DBContext, I applied the syntax you and Christos gave me (`Note note = db.Notes.FirstOrDefault(n => n.NoteId == noteId);` .. and it's working. Thank you :) – FoggyDay Nov 18 '19 at 08:23
Cheers m8! Glad I could help. – Athanasios Kataras Nov 18 '19 at 08:23

EF6: How do I search for an item in a List?

2 Answers2