如何通过 System.Text.Json 从文件加载值并将它们存储为只读？

Question

I want to load settings from a JSON-file via System.Text.Json. These settings should all be readonly after being loaded.

My code so far:

string jsonString = File.ReadAllText(filename);
Settings s = JsonSerializer.Deserialize<Settings>(jsonString);

And the Settings-class:

public class Settings
{
    public decimal A { get; set; }
    public int B { get; set; }
    public double C { get; set; }
    public double D { get; set; }
}

The problem: The values are editable and using private set; does not work because JsonSerializer needs to be able to access the setters.

Answer 1

Create a base class with public set for the serializer and then override them in derived class which does does not allow them to be mutated.

---

I suggest that you change design and make a base class with all the properties mutable and that will be the target of any deserialization operation ( since mutable properties play well with deserialization ). Then a consumer will get the immutable instance via covert/copy/reflect it from that base class.

var bse = JsonConvert.DeserializeObject<MutablePropertyStore>("{ 'PropertyB' : true }");
Console.WriteLine("Base:    " +  bse.ToString());   

var derived = new ImmutablePropertyStore(bse);              
Console.WriteLine("Derived: " + derived.ToString());    

Result

Base:    Property A is 'False' and Property B is 'True'.
Derived: Property A is 'False' and Property B is 'True'.

---

Example .Net Fiddle

Code

public sealed class ImmutablePropertyStore : MutablePropertyStore
{
    public new bool PropertyA { get; private set; }
    public new bool PropertyB { get; private set; }

    public ImmutablePropertyStore() { }

    public ImmutablePropertyStore(MutablePropertyStore ms)
    {
        PropertyA = ms.PropertyA;
        PropertyB = ms.PropertyB;
    }

    public ImmutablePropertyStore(bool propertyA = true, bool propertyB = false)
    {
        PropertyA = propertyA;
        PropertyB = propertyB;
    }

    public override string ToString() 
        => $"Property A is '{PropertyA}' and Property B is '{PropertyB}'."; 
}

public class MutablePropertyStore
{
    public virtual bool PropertyA { get; set;}
    public virtual bool PropertyB { get; set;}

    // Set all defaults here
    public MutablePropertyStore() {  }

    public override string ToString() 
        => $"Property A is '{PropertyA}' and Property B is '{PropertyB}'.";      

}