.net core convert null to empty string in response at ConfigureServices

Question

I have API controller -.net core 3.1-

when I call method I get response object with its properties.

some of this might be null string.

How can I configure my API to return empty string instead of null ?

Can I do this in Startup.cs ?

Edit

I used this option: services.AddMvc().AddJsonOptions(options => { options.JsonSerializerOptions.IgnoreNullValues = true; });

but it'll hide null properties, which I don't want.

I think the easiest way is to set a default value for these properties:`public string Name { get; set; } = "";` — Yinqiu, Feb 03 '21 at 01:48
@Yinqiu I know that. but I want to do it in one place if I can — Mu nt, Feb 03 '21 at 17:58
I would also like to know the answer to this. There must be an option to do this similarly to the ignore function stated in the question. — malthe.w, Aug 12 '22 at 09:14
Found a solution in the end and added it as an answer to your question @Munt — malthe.w, Aug 12 '22 at 12:48

score 2 · Answer 1 · answered Aug 12 '22 at 12:46

Okay so after having the same challenge and researching a bunch, I found out that you can absolutely convert NULLs to empty strings and still have these properties show in your frontend.

I used this other answer (https://stackoverflow.com/a/67286291/11463515) as a reference and did the following.

Step 1:

Create a new class file in the same directory as your Startup.cs file and name it NullToEmptyStringConverter.cs with the following code:

using System;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace API
{
    public class NullToEmptyStringConverter : JsonConverter<string>
    {

        // Override default null handling
        public override bool HandleNull => true;
    
        public override string Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) => 
            reader.TokenType == JsonTokenType.Null ? "" : reader.GetString();

        public override void Write(Utf8JsonWriter writer, string value, JsonSerializerOptions options) =>
            writer.WriteStringValue(value ?? "");
    }
}

Make sure that both your Startup.cs and NullToEmptyStringConverter.cs are using the same namespace!

Step 2:

After creating the NullToEmptyStringConverter.cs file, you can now simply add the following to your services.AddControllers() method so it looks like this:

public void ConfigureServices(IServiceCollection services)
        {
          services.AddControllers()
                .AddJsonOptions(options => 
                {
                    options.JsonSerializerOptions.Converters.Add(new NullToEmptyStringConverter());
                });
        }

And that should be it! With this, all string values that have the value NULL or null in your response will be replaced with "".

.net core convert null to empty string in response at ConfigureServices

1 Answers1

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Step 2: