Skip to main content

c# - How to get column maximum length in a DataTable

Get the maximum length of a column in a DataTable
The DataTable class represents one table of in-memory data. The DataTable objects are conditionally case-sensitive. To create a DataTable programmatically the asp.net developers must first define its schema by adding DataColumn objects to the DataColumnCollection. To add rows to a DataTable, the developers must use the NewRow() method to return a new DataRow object at first. The DataTable also contains a collection of Constraint objects that can be used to ensure the integrity of the data.

The following asp.net c# tutorial code demonstrates how we can get the maximum size/length of columns from a DataTable. So we have to get the maximum length of each DataColumn object within a DataTable instance.

In this example, we used the DataTable class Columns property to get its columns collection as a DataColumnCollection object. Then we loop through the columns collection. In the looping time, we used DataColumnCollection’s Item[Int32] property to get the specified DataColumn instance.

After getting the DataColumn by index we can get its maximum size/length by using the DataColumn class MaxLength property. We also get the specified column’s name by using the DataColumn class ColumnName property.

The DataTable class Columns property gets the collection of columns that belong to this table. The Columns property value is a DataColumnCollection that contains the collection of DataColumn objects for the table. An empty collection is returned if no DataColumn objects exist.

The DataColumnCollection class represents a collection of DataColumn objects for a DataTable. The DataColumnCollection class Item[Int32] property gets the DataColumn from the collection at the specified index.

The DataColumn class MaxLength property gets or sets the maximum length of a text column. This property value is an Int32 which is the maximum length of the column in characters. If the column has no maximum length then the value is -1 and this is the default value.

The DataColumn class MaxLength property is ignored for non-text columns. An ArgumentException exception is raised if the asp.net web developers assign the MaxLength property to a non-string column.
DataColumnMaxLengthFromDataTable.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="System.Data" %>

<!DOCTYPE html>
<script runat="server">
    void Button1_Click(object sender, System.EventArgs e)
    {
        DataTable dt = new DataTable();
        dt.TableName = "Books";

        DataColumn dc1 = new DataColumn();
        dc1.ColumnName = "BookID";
        dc1.DataType = typeof(int);
        dc1.AllowDBNull = false;

        DataColumn dc2 = new DataColumn();
        dc2.ColumnName = "BookName";
        dc2.DataType = typeof(string);
        dc2.MaxLength = 95;

        DataColumn dc3 = new DataColumn();
        dc3.ColumnName = "Author";
        dc3.DataType = typeof(string);
        dc3.MaxLength = 55;

        dt.Columns.AddRange(new DataColumn[] { dc1, dc2,dc3 });

        dt.Rows.Add(new object[] { "1", "Mining the Social Web", "Matthew Russell" });
        dt.Rows.Add(new object[] { "2", "Cassandra: The Definitive Guide", "Eben Hewitt" });
        dt.Rows.Add(new object[] { "3", "Data Analysis with Open Source Tools", "Philipp K. Janert" });

        GridView1.DataSource = dt;
        GridView1.DataBind();

        Label1.Text = "<b><u>Columns with MaxLength in DataTable....</u></b><br />";
        for (int i=0; i< dt.Columns.Count; i++)
        {
            Label1.Text += dt.Columns[i].ColumnName + " || ";
            Label1.Text += dt.Columns[i].MaxLength + "<br/ >";
        }
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>How to get DataColumn MaxLength (maximum length) from DataTable in ado.net</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:DarkBlue; font-style:italic;">
            How to get DataColumn MaxLength
            <br /> programmatically from DataTable in ado.net
        </h2>
        <hr width="450" align="left" color="CornFlowerBlue" />
        <asp:GridView 
            ID="GridView1"
            runat="server"
            BorderColor="Snow"
            ForeColor="SlateBlue"
            Width="525"
            >
            <HeaderStyle BackColor="DarkTurquoise" Height="35" />
            <RowStyle BackColor="PaleTurquoise" BorderStyle="Dotted" BorderWidth="2" />
            <AlternatingRowStyle BackColor="LightBlue" />
        </asp:GridView>
        <br />
        <asp:Label
             ID="Label1"
             runat="server"
             Font-Size="Large"
             ForeColor="Crimson"
             >
        </asp:Label>
        <br />
        <asp:Button 
            ID="Button1"
            runat="server"
            OnClick="Button1_Click"
            Text="Populate GridView"
            Height="45"
            Font-Bold="true"
            ForeColor="DarkBlue"
            />
    </div>
    </form>
</body>
</html>
Labels:

Popular posts from this blog

Restricting Jetpack Compose TextField to Numeric Input Only

Jetpack Compose has revolutionized Android development with its declarative approach, enabling developers to build modern, responsive UIs more efficiently. Among the many components provided by Compose, TextField is a critical building block for user input. However, ensuring that a TextField accepts only numeric input can pose challenges, especially when considering edge cases like empty fields, invalid characters, or localization nuances. In this blog post, we'll explore how to restrict a Jetpack Compose TextField to numeric input only, discussing both basic and advanced implementations. Why Restricting Input Matters Restricting user input to numeric values is a common requirement in apps dealing with forms, payment entries, age verifications, or any data where only numbers are valid. Properly validating input at the UI level enhances user experience, reduces backend validation overhead, and minimizes errors during data processing. Compose provides the flexibility to implement ...
Read more

jetpack compose - TextField remove underline

Compose TextField Remove Underline The TextField is the text input widget of android jetpack compose library. TextField is an equivalent widget of the android view system’s EditText widget. TextField is used to enter and modify text. The following jetpack compose tutorial will demonstrate to us how we can remove (actually hide) the underline from a TextField widget in an android application. We have to apply a simple trick to remove (hide) the underline from the TextField. The TextField constructor’s ‘colors’ argument allows us to set or change colors for TextField’s various components such as text color, cursor color, label color, error color, background color, focused and unfocused indicator color, etc. Jetpack developers can pass a TextFieldDefaults.textFieldColors() function with arguments value for the TextField ‘colors’ argument. There are many arguments for this ‘TextFieldDefaults.textFieldColors()’function such as textColor, disabledTextColor, backgroundColor, cursorC...
Read more

jetpack compose - Image clickable

Compose Image Clickable The Image widget allows android developers to display an image object to the app user interface using the jetpack compose library. Android app developers can show image objects to the Image widget from various sources such as painter resources, vector resources, bitmap, etc. Image is a very essential component of the jetpack compose library. Android app developers can change many properties of an Image widget by its modifiers such as size, shape, etc. We also can specify the Image object scaling algorithm, content description, etc. But how can we set a click event to an Image widget in a jetpack compose application? There is no built-in property/parameter/argument to set up an onClick event directly to the Image widget. This android application development tutorial will demonstrate to us how we can add a click event to the Image widget and make it clickable. Click event of a widget allow app users to execute a task such as showing a toast message by cli...
Read more