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Devexpress Aspx Onrowinserting Get Oldvalues

7 min read Sep 30, 2024
Devexpress Aspx Onrowinserting Get Oldvalues

Mastering Row Insertion and Value Retrieval with DevExpress ASP.NET Controls

As a developer working with DevExpress ASP.NET controls, you may encounter scenarios where you need to access the old values of a row before it is inserted. This is often crucial for tasks such as auditing, data validation, or calculating differences between the original data and the newly entered values. The OnRowInserting event of the DevExpress grid control offers a powerful mechanism to achieve this.

Let's explore how to effectively use the OnRowInserting event in conjunction with retrieving old values for your ASP.NET applications.

Understanding the OnRowInserting Event

The OnRowInserting event is triggered just before a new row is added to your DevExpress grid. It provides you with a prime opportunity to perform actions like:

  • Data Validation: Ensure that the new data meets your predefined criteria before insertion.
  • Auditing: Log the old and new values of the row to maintain a historical record.
  • Calculations: Calculate differences or derive new values based on the existing data.
  • Customizations: Modify the new row's values or handle specific insertion behaviors.

Accessing Old Values: The Key to Effective Handling

Retrieving the original values of a row before it's inserted is essential to perform various operations within the OnRowInserting event. Here's how to achieve this:

1. Utilizing the e.NewValues and e.OldValues Objects:

The OnRowInserting event handler provides two important objects:

  • e.NewValues: Contains the values of the new row being inserted.
  • e.OldValues: Contains the values of the row that was displayed in the grid before the insertion process began.

2. Accessing Specific Values:

You can access specific values from these objects using the field name as an index:

protected void gridView_OnRowInserting(object sender, DevExpress.Web.Data.ASPxDataInsertingEventArgs e)
{
    // Retrieve old value for the "ProductName" field.
    string oldProductName = e.OldValues["ProductName"].ToString();

    // Retrieve new value for the "Quantity" field.
    int newQuantity = Convert.ToInt32(e.NewValues["Quantity"]);

    // Perform actions based on old and new values
    // ...
}

Example: Auditing Row Insertion

Let's illustrate how to use the OnRowInserting event and old values for auditing row insertions. Imagine you need to track changes made to a product inventory table.

Step 1: Define an Audit Table

Create a table in your database to store audit records:

CREATE TABLE AuditLog (
    AuditID INT IDENTITY(1,1) PRIMARY KEY,
    TableName VARCHAR(255),
    Action VARCHAR(50),
    FieldName VARCHAR(255),
    OldValue VARCHAR(255),
    NewValue VARCHAR(255),
    Timestamp DATETIME
);

Step 2: Implement the OnRowInserting Event Handler

In your ASP.NET code-behind file, implement the OnRowInserting event handler:

protected void gridView_OnRowInserting(object sender, DevExpress.Web.Data.ASPxDataInsertingEventArgs e)
{
    // Access old and new values for each field
    foreach (string fieldName in e.NewValues.Keys)
    {
        // Retrieve the old and new values
        string oldValue = e.OldValues[fieldName].ToString();
        string newValue = e.NewValues[fieldName].ToString();

        // Log the changes in the AuditLog table
        // ... 
    }

    // Continue with the insertion process
    e.Cancel = false; // Allow the row to be inserted
}

Step 3: Log Changes to the Audit Table

In the foreach loop, use your preferred method to insert an audit record into the AuditLog table for each field that has changed. This includes specifying the table name, action (INSERT), field name, old value, new value, and the timestamp.

Tips for Effective Implementation

  • Handle Null Values: When retrieving values from e.OldValues, be mindful of null values and handle them appropriately to avoid exceptions.
  • Use a Data Access Layer: Implement a dedicated data access layer (DAL) to abstract database operations and maintain clean code.
  • Custom Validation: Tailor your validation logic within the OnRowInserting event to enforce specific business rules and data integrity.
  • Cancel Insertion: If the validation fails or you want to prevent the insertion, set e.Cancel to true.

Conclusion

The OnRowInserting event in DevExpress ASP.NET grids provides a powerful mechanism to control row insertions, access old values, and perform custom actions before the data is saved. By effectively implementing the OnRowInserting event, you can enhance data integrity, audit changes, and build robust applications.

This empowers you to leverage the full potential of DevExpress ASP.NET controls for data manipulation and management.

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