How Can I Download Excel Files Remotely Using AJAX in MVC Without Page Reloads?

Remote Excel File Download in MVC using AJAX: A Seamless Approach

Handling extensive forms in MVC often requires generating Excel files from specific form data. This article demonstrates how to achieve this efficiently using AJAX, avoiding complete page refreshes.

The AJAX File Download Challenge

Directly downloading files via AJAX isn't feasible. We need a workaround.

The Solution: Server-Side File Generation and AJAX Data Transfer

The solution involves using AJAX to send form data to the server. Server-side code (e.g., using EPPlus or NPOI) creates the Excel file. The file is then stored temporarily as a byte array, and a reference is returned to the client. A subsequent redirect triggers the actual download.

Byte Array Storage and Reference Passing

The generated Excel file is stored as a byte array in the TempData container, identified by a unique reference. This reference (along with the filename) is sent back as JSON to the AJAX function. The AJAX function then redirects to a separate controller action to retrieve the file from TempData and initiate the download.

Step-by-Step Implementation

1. Controller Action for File Generation:

This action receives the form data, generates the Excel file using a library like EPPlus, stores it in TempData as a byte array, and returns a JSON object containing a unique identifier and the filename.

public ActionResult PostReportPartial(ReportVM model)
{
    // Generate Excel file using EPPlus or NPOI
    ExcelPackage workbook = new ExcelPackage();
    // ... file generation logic ...

    // Store file in TempData
    string handle = Guid.NewGuid().ToString();
    TempData[handle] = workbook.GetAsByteArray();

    return Json(new { FileGuid = handle, Filename = "ReportOutput.xlsx" });
}

2. AJAX Call and Redirection:

The AJAX call sends the form data to the PostReportPartial action. Upon successful response, it redirects to another controller action to handle the download.

$.ajax({
    // ... AJAX settings ...
    success: function (response) {
        window.location = '/Report/Download?fileGuid=' + response.FileGuid + '&filename=' + response.Filename;
    }
});

3. Controller Action for File Download:

This action retrieves the file from TempData using the unique identifier, and sends it to the client for download.

[HttpGet]
public ActionResult Download(string fileGuid, string fileName)
{
    if (TempData[fileGuid] != null)
    {
        byte[] data = TempData[fileGuid] as byte[];
        return File(data, "application/vnd.ms-excel", fileName);
    }
    else
    {
        return new EmptyResult();
    }
}

This method ensures efficient, user-friendly Excel file downloads without page reloads, leveraging server-side processing for optimal performance. No physical files are permanently stored on the server.

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