How to set Access column value to 0 (default) on a new created DB column? C#
So I have read multiple posts about my question but I cant find the right solution for it.
I've got a form in which a user can add a custom column to a database. This column is always of type currency with the currency type of Euro.
I thought I did the trick by creating this query:
string query = "ALTER TABLE Uitgaven ADD COLUMN [" + textBox16.Text + "] MONEY DEFAULT 0";
command.CommandText = query;
command.ExecuteNonQuery();
At my initialize I have a functions that add my database values to a listbox with a reader, it also transforms the read values to the right output, see here the code for it:
while (reader2.Read())
{
for (int i = 0; i < reader2.FieldCount; i++)
{
y = reader2.GetName(i).Length;
if (reader2.GetName(i) != "Maand" && reader2.GetName(i) != "Uitgaven Id")
{
euro_display = (decimal)(reader2.GetValue(i));
ListBox2_add.Items.Add(reader2.GetName(i) + "€".PadLeft(31 - y) + euro_display.ToString("0.00", CultureInfo.CreateSpecificCulture("nl-NL")));
comboBox1.Items.Add(reader2.GetName(i));
totaal_uitgaven += reader2.GetDecimal(i);
}
}
}
This above function however isn't working when someone adds a custom field with my first query code. This above function needs a value in the database and for some reason the query code in the beginning of my code isn't setting the new added column values to the default 0 (0,00 euro).
I try'd multiple things but non of them see to do the trick.
I modified my query to (among others):
string query = "ALTER TABLE Uitgaven ADD COLUMN [" + textBox16.Text + "] MONEY DEFAULT 0 NOT NULL";
string query = "ALTER TABLE Uitgaven ADD COLUMN [" + textBox16.Text + "] Y DEFAULT 0 NOT NULL"; `
(read somewhere that Y was the currency for Euro--not sure tough)
I also try'd to add a second query after my first query to set its value of the created column:
string query2 = "ALTER TABLE Uitgaven ADD DEFAULT 0 FOR [" + textBox16.Text + "]";
string query2 = "INSERT INTO Uitgaven ([" + textBox16.Text + "] ) VALUES (0)";
This all didn't work though.. Anyone has a clue how I can set the values of a custom created column to a default 0 or just to 0 (currency - euro)?
Thanks in advance!
Your problem is related to the fact that after adding the new column, the old records are not updated with the default value. They contains a NULL. You need to add an UPDATE query to your creation routine that sets the DEFAULT for all existing records
string query = "ALTER TABLE Uitgaven ADD COLUMN [" +
textBox16.Text + "] MONEY DEFAULT 0";
command.CommandText = query;
command.ExecuteNonQuery();
command.CommandText = "UPDATE TABLE Uitgaven SET [" + textBox16.Text + "] = 0";
command.ExecuteNonQuery();
Another approach could be to check for null values and act accordingly if one null is detected
while (reader2.Read())
{
for (int i = 0; i < reader2.FieldCount; i++)
{
string fieldname = reader2.GetName(i);
y = fieldname.Length;
if (fieldname != "Maand" && fieldname != "Uitgaven Id")
{
decimal euro_amount = reader.IsDbNull(i) ? 0m : reader2.GetDecimal(i);
ListBox2_add.Items.Add(fieldname + "€".PadLeft(31 - y) + euro_amount.ToString("0.00", CultureInfo.CreateSpecificCulture("nl-NL")));
comboBox1.Items.Add(fieldname);
totaal_uitgaven += euro_amount;
}
}
}