使用ExecuteReader遍历行

Question

I'm stumped, I am trying to fill 5 textboxes from a database, not all 5 will always have data.

Example:

ID | ItemID | QType

1 | 10 | 2 Boxes

2 | 10 | 6 Boxes

3 | 11 | 1 Case

In this example it would fill QuantityType1TxtBox with 2 Boxes and QuantityType2TxtBox with 6 Boxes, while leaving the other three textboxes blank.

The following error I get when I try to run this code is: Index was outside the bounds of the array.

This error happens on this line: QuantityType2TxtBox.Text = rdr.GetString(1);

SqlCommand cmd = new SqlCommand(@"SELECT QType FROM InventoryQType
                                                WHERE ItemID = '" + itemID + "'", conn);
conn.Open();
SqlDataReader rdr = cmd.ExecuteReader();

while (rdr.Read())
{
    QuantityType1TxtBox.Text = rdr.GetString(0);
    QuantityType2TxtBox.Text = rdr.GetString(1);
    QuantityType3TxtBox.Text = rdr.GetString(2);
    QuantityType4TxtBox.Text = rdr.GetString(3);
    QuantityType5TxtBox.Text = rdr.GetString(4);
}
rdr.Close();

Answer 1

I'm not sure my switch statement is the right way to do it for this, but I think the rest of this code is useful to show you parameters and using statements.

string sql = @"SELECT QType FROM InventoryQType WHERE ItemID=@id";
using (SqlConnection conn = new SqlConnection("[put your connection string here, or reference to web.config]")) {
    conn.Open();
    using (SqlCommand cmd = new SqlCommand(sql, conn)) {
        cmd.Parameters.Add("@id", System.Data.SqlDbType.VarChar).Value = itemID;
        SqlDataReader rdr = cmd.ExecuteReader();
        int loop = 1;
        while (rdr.Read()) {
            switch(loop){
                case 1:
                    QuantityType1TxtBox.Text = (string)rdr["QType"];
                    break;
                case 2:
                    QuantityType2TxtBox.Text = (string)rdr["QType"];
                    break;
                case 3:
                    QuantityType3TxtBox.Text = (string)rdr["QType"];
                    break;
                case 4:
                    QuantityType4TxtBox.Text = (string)rdr["QType"];
                    break;
                case 5:
                    QuantityType5TxtBox.Text = (string)rdr["QType"];
                    break;
                default:
                    break;
            }
            loop++;
        }
    }
    conn.Close();
}

Also of note, your itemID seems to be a varchar in your example. I assume it is actually an int, so you'll need to change the 'VarChar' part of the Parameter to be 'Int' if that is true.

Answer 2

Lots of ways to do this, but a crude implementation to get you started might look something like:

List<string> values;
while(rdr.Read())
{
    values.Add(rdr.GetString(0));
    if (values.Count == 5) break;
}

if (values.Count > 0) QuantityType1TxtBox.Text = values[0];
if (values.Count > 1) QuantityType2TxtBox.Text = values[1];    
if (values.Count > 2) QuantityType3TxtBox.Text = values[2];
if (values.Count > 3) QuantityType4TxtBox.Text = values[3];
if (values.Count > 4) QuantityType5TxtBox.Text = values[4];

You might want to consider (a) separating your data access code into a separate class / method that returns a list of values, and (b) putting your text boxes into a collection so you don't need repeated code to assign values to them.

Answer 3

The SQL query you are using to retrieve the data only returns the QType field, so the SqlDataReader only has 1 column.

Because you are requesting the second column by calling rdr.GetString(1) , an Index out of bounds exception occurs.

I would edit your select statement to name each of the fields you would like to put in each text box, so that the indexing would work as you expect.

Finally, if you retrieve more than 1 row of data with the code above, at the end of this method the text boxes would contain the data from the last record - this is because the previous records would be overwritten, since you are assigning the Text property of each text box repeatedly.

Answer 4

Fix your code like this:

var values = new List<string>();
while (rdr.Read())
{
   values.add(rdr.GetString(0));
}