reading arrays of objects from appsettings.json

Question

reading arrays of objects from appsettings.json

team upsilon 36

{  
  "Logging": {  
    "LogLevel": {  
      "Default": "Information",  
      "Microsoft.AspNetCore": "Warning"  
    }  
  },  
  "AllowedHosts": "*",  
  "TimeInterval": [  
     {  
      "Title": "6 hours",  
      "Hours": 6  
    },  
    {  
      "Title": "1 day",  
      "Hours": 24  
    }  
  ]  
}

Above is what i have in my appsettings.json. I am able to read single properties of objects however i cant read the whole array at once. Preferably i'd like to parse it into a TimeInterval object too. How can I do this? I am using blazor server side.

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Answer 1

You should use Dependency Injection and the .NET Configuration system:

Inject IConfiguration, and store the instance in a member/variable like Configuration
Add the using Microsoft.Extensions.Configuration statement
Read the app settings like this: var intervals = Configuration.GetSection("TimeInterval").Get<List<TimeInterval>>();

You can also use options pattern to get the settings. But to avoid a long post, I'll just share two examples on how to get configs in the page or in a page model. Fore more information, take a look at links at the bottom of the post.

Example 1 - Getting configuration in a Blazor Page

Assuming you have the following class:

public class TimeInterval  
{  
    public string Title { get; set; }  
    public int Hours { get; set; }  
}

Then in a page, you can inject IConfiguration and read the settings:

@page "/"  
@using Microsoft.Extensions.Configuration  
@inject IConfiguration Configuration  
<h1>Hello, world!</h1>  
<ul>  
@{  
    var intervals = Configuration.GetSection("TimeInterval").Get<List<TimeInterval>>();  
    foreach (var item in intervals)  
    {  
        <li>@item.Title: @item.Hours Hours</li>  
    }  
}  
</ul>  
Welcome to your new app.

Example 2 - Getting configuration in a PageModel class:

Inject the IConfiguration and read settings like this:

using Microsoft.AspNetCore.Mvc.RazorPages;  
using Microsoft.Extensions.Configuration;  
using System.Collections.Generic;  
  
namespace WebApplication1.Pages  
{  
    public class IndexModel : PageModel  
    {  
        public IConfiguration Configuration;  
        public IndexModel(IConfiguration configuration)  
        {  
            Configuration = configuration;  
        }  
        public void OnGet()  
        {  
            var intervals = Configuration.GetSection("TimeInterval").Get<List<TimeInterval>>();  
        }  
    }  
}

More information:

team upsilon 36 Reputation points

2022-07-29T07:19:51.473+00:00

Thank you this is what i was looking for. I had previously tried this, but it wouldnt work, the list would return empty or it would be an array with the right length but with null values. Turns out having a constructor in the TimeInterval class was the problem. I have no idea why an ordinary constructor would cause this if you do please tell :). Edit: So it wasnt the existence of a constructor that was the problem, but a lack of an empty constructor with no parameters.
Reza Aghaei 4,986 Reputation points MVP Volunteer Moderator

2022-07-29T09:28:09.783+00:00

Thanks for the feedback. You have figured out the problem yourself; yes it's lack of parameterless constructor. Classes have implicit public parameter constructor until you create a non-public constructor or a constructor with a parameter. A class needs a parameterless constructor for serialization.
Reza Aghaei 4,986 Reputation points MVP Volunteer Moderator

2022-07-29T09:36:34.02+00:00

One point about using json deserializer to read appsettings; you can of course make it working, but you should almost always avoid reading appsettings using jsondesrializer. It's a very bad practice.
Instead, as a best practice, you should use DI and the .NET Config system features.

Keep in mind, AppSettings is part of the .NET Configuration system which has different providers and even if the settings come from a secret manager, from an xml file, etc. the IConfiguration interface with help of different built-in providers can read those settings without any problem, without changing anything in your code. But if you use json deserializer, then if you want to read settings from secret manager or other providers you need to change app code.

Answer 2

Karen Payne MVP 35,586 Volunteer Moderator

One option using System.Text.Json

public class RootSettings  
{  
    public Timeinterval[] TimeInterval { get; set; }  
}

Read

Timeinterval[] result =  
    JsonSerializer.Deserialize<RootSettings>(  
        File.ReadAllText("appsettings.json")).TimeInterval;

team upsilon 36 Reputation points

2022-07-29T07:13:21.917+00:00

This works however I've had issues reading from files in different environments, file not found exceptions etc.

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reading arrays of objects from appsettings.json

Example 1 - Getting configuration in a Blazor Page

Example 2 - Getting configuration in a PageModel class:

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