---
title: "Http post request FromBody string always binding null in dotnet"
description: "Explains why a [FromBody] string parameter in ASP.NET Core always ends up null. The root cause is that the value must be a JSON-formatted string, with a guard to prevent double serialization."
canonical_url: "https://blog.markkulab.net/en/post/dotnet-post-frombody-string-always-binding-null"
author: "Mark Ku"
author_url: "https://blog.markkulab.net/en/author/mark-ku"
site: "Mark Ku's Tech Notes"
date_published: "2022-11-06 01:01:01 +0800"
category: ".NET Core"
tags: ["dotnet", "asp.net core", "frombody", "json", "binding", "api", "bug"]
language: "en"
license: "CC BY 4.0"
license_url: "https://creativecommons.org/licenses/by/4.0/"
attribution: "when reusing or quoting, credit the author and link back to the original"
---

# Http post request FromBody string always binding null in dotnet

## Problem
```
[HttpPost]
public string Book([FromBody] string test) // binding string always is null 
{
return test;
}
```
## Root cause

When having [FromBody]attribute, the string sent should not be a raw string, but rather a JSON string as it includes the wrapping quotes:

```
'test string' or "test string"
```

## So you can use JSON.stringify() 

```
JSON.Stringify('test string') // will be => "test string"
```

## But cannot do JSON.Stringify twice
```
let x= JSON.stringify(JSON.stringify('test string')) // will be => '"\\"test string\\""'
```

## Avoid execute twice

```
export const isJsonString = (str: string) => {
  try {
    JSON.parse(str);
  } catch (e) {
    return false;
  }
  return true;
};
```

---

## About this article and its author

Originally published on [Mark Ku's Tech Notes](https://blog.markkulab.net/en/post/dotnet-post-frombody-string-always-binding-null)

License: [CC BY 4.0](https://creativecommons.org/licenses/by/4.0/) — when reusing or quoting, credit the author and link back to the original

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