CODEWITHSUNDEEP
c#entity-framework
solmaz ahamdi
solmaz ahamdi

Reputation: 150

Querying in Entity Framework for fill combobox of foreign key

I have a ComboBox of provinces :

public Form1()
{
    InitializeComponent();
    using (AbEntities c = new AbEntities())
    {
        comboBox1.DataSource = c.tbl_Province.ToList();
        comboBox1.ValueMember = "ID";
        comboBox1.DisplayMember = "Province";
    }
}

Now I want to list cities for each province in another combobox.

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (comboBox1.SelectedValue.ToString() != null)
    {
        int pvc = Convert.ToInt32(comboBox1.SelectedValue.ToString());
        string sqlString = "SELECT ID,City FROM tbl_City Where ProvinceID = pvc"

        using (AbEntities c = new AbEntities())
        {
            comboBox2.DataSource = c.tbl_City.ToList();
            comboBox2.ValueMember = "ID";
            comboBox2.DisplayMember = "City";
        }
    }
}

I wrote the following query. But cities are not filtered

Upvotes: 1

Views: 135

Answers (2)

Mong Zhu
Mong Zhu

Reputation: 23732

I don't see any filtering in your code. May be you should apply some like this:

comboBox2.DataSource = c.tbl_City.Where(x=>x.ProvinceID == pvc).ToList();

Explanation:

The loose SQL-query string in your code has no application. Since your post is tagged with entity-framework I assume that AbEntities is a DataContext. In this case tbl_City implements the IQueryable interface and allows you to call Where directly in your code. In this example I used the method syntax. The ToList() call will execute the query and materialize the results. This can also be accomplished using the query syntax:

comboBox2.DataSource = (from   x in c.tbl_City
                        where  x.ProvinceID == pvc
                        select x).ToList();

Upvotes: 1

Stefan
Stefan

Reputation: 17658

You need to query your DbSet, e.g.:

c.tbl_City.Where(c => c.ProvinceID == pvc).ToList();

Further:

there is no relation between the SQL statement and the filter.

You might want to read something about linq,

And here is more about EF: http://www.entityframeworktutorial.net/querying-entity-graph-in-entity-framework.aspx

Upvotes: 1

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