I could not write the SQL query with linq.can you help me?

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Purpose: To select a category in the combobox, to search for the information appropriate to the selected category in the textbox and finally to display it in the listbox. I want to write these codes with Linq.

C#

private void CBkategori_SelectedIndexChanged(object sender, EventArgs e)
        {
            string category = CBkategori.Text;
            query = "select name from items where category='" + category + "'";
            listbox(query);
        }

private void txtarama_TextChanged(object sender, EventArgs e)
        {
string category = CBkategori.Text;
        query = "select name from items where category='" + category + "' and name like '"+txtsearch+"%'";
        listbox(query);
}

private void listbox(string query)
{
    ListBox.items.clear();
    DataSet ds = fn.getData(query);
    for (int i = 0; i < ds.Tables[0].Rows.Count; i++) ;
    {
        ListBox.items.Add(ds.Tables[0].Rows[i][0].ToString());
    }
}

What I have tried:

C#

string category= CBkategori.Text;
            item = new item();
            var query = from item in db.item
                        where item.name.Contains(kategori)
                        select item;
            listbox.DataSource = query.ToList();

Posted 15-Jan-21 10:33am

kadiraydeger

Updated 16-Jan-21 1:10am

Maciej Los

v2

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Comments

Maciej Los 16-Jan-21 5:50am

Your question is not clear. Can you provide more details?

Richard Deeming 18-Jan-21 6:14am

Your code is vulnerable to SQL Injection[^]. NEVER use string concatenation to build a SQL query. ALWAYS use a parameterized query.

Everything you wanted to know about SQL injection (but were afraid to ask) | Troy Hunt[^]
How can I explain SQL injection without technical jargon? | Information Security Stack Exchange[^]
Query Parameterization Cheat Sheet | OWASP[^]

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RickZeeland · Answer 1 · 2021-01-16T01:10:00

Here is an example from: Queries in LINQ to DataSet - ADO.NET | Microsoft Docs[^]

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable products = ds.Tables["Product"];

IEnumerable<DataRow> productsQuery =
    from product in products.AsEnumerable()
    select product;

IEnumerable<DataRow> largeProducts =
    productsQuery.Where(p => p.Field<string>("Size") == "L");

Console.WriteLine("Products of size 'L':");
foreach (DataRow product in largeProducts)
{
    Console.WriteLine(product.Field<string>("Name"));
}

Another (recommend) way is using a BindingSource, see example here:
Creating a DataTable From a Query (LINQ to DataSet) - ADO.NET | Microsoft Docs[^]