C# – JSON object contains a trailing comma at the end which is not supported

Problem When you deserialize JSON, you get the following error: The JSON object contains a trailing comma at the end which is not supported in this mode. Change the reader options. JSON properties are separated with commas. A trailing comma is one that has no properties after it. Here’s an example of a trailing comma: … Read more

C# – Deserialize JSON to a derived type

The simplest way to deserialize JSON to a derived type is to put the type name in the JSON string. Then during deserialization, match the type name property against a set of known derived types and deserialize to the target type. System.Text.Json doesn’t have this functionality out of the box. That’s because there’s a known … Read more

C# – Populate an existing object with JSON

Normally when you’re working with JSON, you deserialize it to a target type and get back an initialized and fully populated object. How about if you need to initialize an object yourself, and then populate it with JSON later? For example, let’s say you want to load the following JSON array into a case-insensitive HashSet: … Read more

C# – How to ignore JSON deserialization errors

One error during deserialization can cause the whole process to fail. Consider the following JSON. The second object has invalid data (can’t convert string to int), which will result in deserialization failing: With Newtonsoft, you can choose to ignore deserialization errors. To do that, pass in an error handling lambda in the settings: This outputs … Read more

C# – Deserialize a JSON array to a list

When you’re working with a JSON array, you can deserialize it to a list like this: This deserializes all of the objects in the JSON array into a List<Movie>. You can use this list object like usual. Note: All examples will use System.Collections.Generic and System.Text.Json. I’ll exclude the using statements for brevity. Example – JSON … Read more

C# – Deserializing JSON with quoted numbers

There are two ways to represent numbers in JSON: as number literals (ex: 123) or as quoted numbers (ex: “123”). In this article, I’ll explain how quoted numbers are handled during deserialization in Newtonsoft and System.Text.Json and how to change the behavior. At the end, I’ll show how to write quoted numbers during serialization. Quoted … Read more

JavaScript – Post form data to a web API asynchronously

You can post form data asynchronously by using fetch() + FormData, like this: FormData parses the form element into an array of key/value pairs for you. This results in sending the following request: When you set the request body to a FormData object, it sets the content-type to multipart/form-data. You can post the data in … Read more

Get SQL Server query results as JSON

The simplest way to get query results as JSON is to use FOR JSON PATH in the query (note: this was added in SQL Server 2016): It returns the results as a single JSON string with one JSON object per row: Note: SQL Server returns the JSON without indenting. All examples in this article show … Read more

C# – How to update appsettings.json programmatically

You have to overwrite the appsettings.json file to be able to update values programmatically. You have to deal with the whole file, not individual parts of it. The process can be summarized in the following steps: Load appsettings.json and deserialize it into an object. Update properties on the object. Serialize the object into a JSON … Read more

Deserializing JSON that contains an embedded JSON string

When you send mail, you put a letter in an envelope and put routing information on the envelope. The postal service uses the routing information to deliver the envelope to a specific mailbox. The mailbox owner then opens the envelope and reads the letter. Sometimes you may need to deal with the JSON equivalent of … Read more