# Merging Templates with MailMerge with Different Merge Field Settings in C#
> This article shows how to merge templates with different merge field settings using the MailMerge class. The various settings allow for the removal of unused fields or the possibility to make changes to fields after the merge process.
- **Author:** Bjoern Meyer
- **Published:** 2023-12-16
- **Modified:** 2025-11-16
- **Description:** This article shows how to merge templates with different merge field settings using the MailMerge class. The various settings allow for the removal of unused fields or the possibility to make changes to fields after the merge process.
- **4 min read** (727 words)
- **Tags:**
- ASP.NET Core
- ASP.NET
- Document Editor
- MailMerge
- **Web URL:** https://www.textcontrol.com/blog/2023/12/16/merging-templates-with-mailmerge-with-different-merge-field-settings/
- **LLMs URL:** https://www.textcontrol.com/blog/2023/12/16/merging-templates-with-mailmerge-with-different-merge-field-settings/llms.txt
- **LLMs-Full URL:** https://www.textcontrol.com/blog/2023/12/16/merging-templates-with-mailmerge-with-different-merge-field-settings/llms-full.txt
---
When providing users with the ability to modify documents after they have been generated by MailMerge, there are several options you can utilize.
### Merge Data
Consider the following scenario where a particular JSON data source is being used for template creation.
```
[
{
"id": 1,
"customer": {
"id": 1,
"name": "John Doe",
"street": "123 Main St",
"city": "Anytown",
"state": "TX",
"zip": "12345"
},
"items": [
{
"id": 1,
"name": "Widget",
"price": 9.99,
"quantity": 2
},
{
"id": 2,
"name": "Thing",
"price": 5.99,
"quantity": 5
},
{
"id": 3,
"name": "Gadget",
"price": 199.99,
"quantity": 1
}
],
"total": 0
},
{
"id": 2,
"customer": {
...
```
The controller loads this JSON and passes it to the view, where it is loaded into the editor to populate the dropdowns with the correct merge field names.
```
public IActionResult Index()
{
string json = System.IO.File.ReadAllText("App_Data/data.json");
ViewBag.Data = json;
return View();
}
```
### Sending Data to Endpoint
The view code loads the JSON and makes a jquery AJAX call to send the create template to the *Merge* endpoint.
```
@using TXTextControl.Web.MVC
@Html.TXTextControl().TextControl().LoadDataFromJson(ViewBag.Data).Render()
@section Scripts {
}
```
The editor enables users to create the template by adding available merge fields and merge blocks.
After the merge process, the returned document contains merged content and the field functionality is removed.
### Preserve Empty Fields
Now consider that there are fields in the template that have no data. By default, these fields are removed after the merge.
The following screenshot shows the merged document with the empty "MERGEFIELD" field removed.
By setting the RemoveEmptyFields property to false, these fields are retained and the field functionality is preserved.
```
using (MailMerge mm = new MailMerge())
{
mm.TextComponent = tx;
mm.RemoveEmptyFields = false;
// load json data
string json = System.IO.File.ReadAllText("App_Data/data.json");
// merge data
mm.MergeJsonData(json, true);
}
```
> **Learn More**
>
> The MailMerge class provides several settings to control the merge process and formatting in the resulting document. There are several switches to control how text fields, blocks, images, and blank lines are handled. This article provides an overview of when and how to use each option.
>
> [MailMerge Class Settings Explained ](https://www.textcontrol.com/blog/2019/12/05/mailmerge-settings-explained/llms-full.txt)
### Preserve Field Functionality
But now consider a scenario in which you want the merged fields to be editable after the merge process is complete. In this case, there is not a property that is available, but there is a typical workflow that allows this to be realized. Each field provides an event that fires when fields are merged. It is usually used to change the contents of the field after the merge.
The advantage of this process is that the functionality of the field is maintained after the field is changed.
The following code attaches the event to the MailMerge object, passing the merged content back to the field.
```
[HttpPost]
public IActionResult Merge([FromBody] Content results)
{
using (TXTextControl.ServerTextControl tx = new TXTextControl.ServerTextControl())
{
tx.Create();
tx.Load(Convert.FromBase64String(results.Data), TXTextControl.BinaryStreamType.InternalUnicodeFormat);
using (MailMerge mm = new MailMerge())
{
mm.TextComponent = tx;
mm.FieldMerged += Mm_FieldMerged;
// load json data
string json = System.IO.File.ReadAllText("App_Data/data.json");
// merge data
mm.MergeJsonData(json, true);
}
tx.Save(out byte[] data, TXTextControl.BinaryStreamType.InternalUnicodeFormat);
return Ok(Convert.ToBase64String(data));
}
}
private void Mm_FieldMerged(object sender, MailMerge.FieldMergedEventArgs e)
{
e.MergedField = e.MergedField;
}
```
As a result, the merge fields are populated, but the field functionality remains intact.
This allows users to modify these fields and other content and merge the template again Another use case is previewing live data during the template creation process without losing field functionality.
---
## About Bjoern Meyer
As CEO, Bjoern is the visionary behind our strategic direction and business development, bridging the gap between our customers and engineering teams. His deep passion for coding and web technologies drives the creation of innovative products. If you're at a tech conference, be sure to stop by our booth - you'll most likely meet Bjoern in person. With an advanced graduate degree (Dipl. Inf.) in Computer Science, specializing in AI, from the University of Bremen, Bjoern brings significant expertise to his role. In his spare time, Bjoern enjoys running, paragliding, mountain biking, and playing the piano.
- [LinkedIn](https://www.linkedin.com/in/bjoernmeyer/)
- [X](https://x.com/txbjoern)
- [GitHub](https://github.com/bjoerntx)
---
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