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The simplest way to make a copy of a dictionary is to use the copy constructor. You pass the dictionary you want to copy to the new dictionary’s constructor, like this: Note: If you’re using a non-default comparer, you’ll want to pass it to the copy constructor (i.e. new Dictionary(d, d.Comparer)). The copy constructor handles … Read more
I’ll show examples of how to deserialize JSON to dictionaries in different scenarios. Deserializing to Dictionary<string, string> When your JSON object has properties with simple string values (as opposed to nested objects), you can deserialize to Dictionary<string, string>. Here’s an example. Consider the following simple JSON object: Note: In all examples, I’ll show the pretty-printed … Read more
When you want to convert a dictionary to a JSON string, you can use the built-in JsonSerializer (from System.Text.Json) to serialize the dictionary. Here’s an example: Note: This is passing in WriteIndented=true to pretty print the JSON string for readability. This serializes the dictionary to a JSON string with the following format: I’ll show more … Read more
Converting a JSON string to an object is referred to as deserialization. You can do this with a JSON serializer. There are two primary options: I’ll show examples by deserializing the following Movie JSON to a Movie object: Movie JSON: Movie class (properties match JSON): Using JsonSerializer.Deserialize() (in System.Text.Json) To deserialize with the built-in JsonSerializer.Deserialize(), … Read more
There are two ways to serialize an object’s properties to JSON in alphabetical order using System.Text.Json: I’ll show how to do these two options below. Option 1 – Manually alphabetize with JsonPropertyOrder You can specify the exact serialization ordering by using the JsonPropertyOrder attribute. Therefore, to serialize in alphabetical order, first arrange the properties in … Read more
System.Text.Json doesn’t support serializing / deserializing multidimensional arrays. When you try, it throws an exception like this – System.NotSupportedException: The type ‘System.Int[,] is not supported. You have three options: In this article, I’ll show an example of how to create a custom JsonConverter that handles multidimensional arrays. In this example, I’ll specifically show how to … Read more
When you send a request to ASP.NET with a JSON body, you get the following exception: System.Text.Json.JsonException: The JSON value could not be converted to System.String. Path: $ | LineNumber: 0 | BytePositionInLine: 1. You can’t deserialize JSON to a string. You’re either using a string parameter with [FromBody] or your model has a string … Read more
There are three ways to update a file’s content: Which option you pick depends on the file’s format and size. For example, if you’re writing to an existing CSV file, you’d append new lines to the end of the file. If you’re updating a JSON file, you’d read all the JSON content, make changes, then … Read more
Input formatters are used to deserialize the request body to a model object (which is then passed into an action method). There are built-in input formatters for handling JSON and XML. You can add your own input formatter when you want to customize request body deserialization. There are two scenarios where a custom InputFormatter would … Read more
When you use ConfigurationSection.Get() to load an object from appsettings.json, it returns null if the section doesn’t exist. Since you’re probably not expecting this to be null, this can lead to problems surfacing in unexpected places, such as getting a NullReferenceException: Note: If you’re using ASP.NET Core, you’ll be referring to the config via builder.Configuration … Read more
Let’s say you have the following JSON: When you go to deserialize it, you notice that all or some of its properties are null (or default for value types): This outputs the following (because person.Name is null and person.Pets is 0): The data is definitely there, so why did it set these properties to null … Read more
By default, null properties are included during JSON serialization like this: There are two ways to ignore null properties: In this article, I’ll show examples of these two ways to ignore null properties. I’ll show how to do it with System.Text.Json and Newtonsoft. Ignore null properties with System.Text.Json Use JsonIgnoreCondition.WhenWritingNull to ignore null properties. You … Read more
When you don’t want to create classes for JSON (de)serialization, one option is to use JsonNode. This allows you work with JSON as a mutable DOM that consists of JsonNode objects (JsonObject, JsonArray, JsonValue). You can use it to read, write, and modify JSON. Here’s an example. Let’s say you have the following JSON that … Read more
Problem details (RFC7807) is a standardized error response format that has a Content-Type of application/problem+json, an error response code (i.e. 400 – Bad Request), and has a response body that looks like this: This can be extended to include any number of properties. The example shown above comes from the default way ASP.NET Core returns … Read more
There are many built-in model validation attributes available – such as [Required] and [Range] – which you can use to handle most validation scenarios. When these aren’t sufficient, you can create a custom validation attribute with your own validation logic. I’ll show an example of how to do that. 1 – Subclass ValidationAttribute and implement … Read more
Problem When you deserialize JSON with a “trailing comma”, 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 … Read more
It’s always a good idea to validate data coming into your web API. There are two steps you can do to guard against invalid data: Here’s an example of using model validation attributes: When a request comes in, the framework does two things: Let’s say you send a request with invalid data (boxOfficeMillions is outside … Read more
Postman is a great tool for web development. You can send a request to any web API, look at the response details, and reuse the the request later (which saves lots of effort!). This is useful for testing your own web API, or for when you’re integrating with a third-party API and want to try … Read more
When JSON property names and class property names are different, and you can’t just change the names to match, you have three options: These options affect both deserialization and serialization. Let’s say you have the following JSON with camel-cased property names: Here’s an example of using the JsonPropertyName attribute: Note: The Newtonsoft equivalent is [JsonProperty(“title”)] … Read more
When your class has multiple constructors, you can use the JsonConstructor attribute to specify which constructor to use during deserialization. Here’s an example. The Person class has two constructors. I put the JsonConstructor attribute on one of the constructors: Note: JsonConstructor for System.Text.Json was added in .NET 5. Now deserialize a JSON string to the … Read more
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
You can use the JsonDocument class when you want to read and process JSON without having to deserialize the whole thing to an object. For example, let’s say you have the following JSON object representing wind variables: Now let’s say you’re only interested in the wind speed. Instead of having to deserialize this into a … Read more
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
One error during JSON 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 … Read more
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