C#•4mo ago

✅ Json Validation and Populating with Nulls if Missing

Hi I am trying to validate an input json against a C# object model. There are instances where sometimes nested properties are not a part of this input json and I'd been asked to ensure the json has the correct structure and populate missing props with nulls as values. Anyone encounter something like this before?

10 Replies

Pobiega•4mo ago

Make your models props nullable where they are optional. Deserialize to the model. Non-existing props will be given null values. Serialize the model instance, but with the "write nulls" option turned on. Shouldnt that solve your issues?

eric bonitoOP•4mo ago

The effort here is mainly to homogenize input jsons ahead of deserialization as it seems like this could be a simple (but maybe not)

Pobiega•4mo ago

and these "jsons" are... strings? currently? it seems kinda backwards to spend quite a bit of effort to analyze and homogenize your strings before deserializing, if the only goal with doing that is setting a bunch of properties to null. Let the deserializer handle that instead by correctly modelling your data with nullability indicators - its then automatic as part of deserialization

eric bonitoOP•4mo ago

Yes and that is true if it is indeed quite a bit of effort which is what I am starting to see (deep nesting and arrays)

Pobiega•4mo ago

you'd essentially have to build a json parser, and somehow teach it the shape of your models

eric bonitoOP•4mo ago

I hoping to just create a newtonsoft JObject from the json string file and compare against a defined JSchema (currently generated) with conditions to infill missing objects or properties with nulls. But configuring this is a bit challenging with deeper nesting

Pobiega•4mo ago

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

// John has no height
var json =
    """
    {
        "name": "John",
        "age": 30,
        "nested": {
            "car1": "Ford",
            "car2": "BMW",
            "car3": "Fiat"
        }
    }
    """;

var jsonOptions = new JsonSerializerOptions(JsonSerializerDefaults.Web)
{
    DefaultIgnoreCondition = JsonIgnoreCondition.Never,
    WriteIndented = true
};

var model = JsonSerializer.Deserialize<Person>(json, jsonOptions);
var serialized = JsonSerializer.Serialize(model, jsonOptions);
Console.WriteLine(serialized);

public class Person
{
    public required string Name { get; init; }
    public required int Age { get; init; }
    public int? Height { get; set; }
    public NestedClass? Nested { get; set; }
}

public class NestedClass
{
    public string? Car1 { get; set; }
    public string? Car2 { get; set; }
    public string? Car3 { get; set; }
}

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

// John has no height
var json =
    """
    {
        "name": "John",
        "age": 30,
        "nested": {
            "car1": "Ford",
            "car2": "BMW",
            "car3": "Fiat"
        }
    }
    """;

var jsonOptions = new JsonSerializerOptions(JsonSerializerDefaults.Web)
{
    DefaultIgnoreCondition = JsonIgnoreCondition.Never,
    WriteIndented = true
};

var model = JsonSerializer.Deserialize<Person>(json, jsonOptions);
var serialized = JsonSerializer.Serialize(model, jsonOptions);
Console.WriteLine(serialized);

public class Person
{
    public required string Name { get; init; }
    public required int Age { get; init; }
    public int? Height { get; set; }
    public NestedClass? Nested { get; set; }
}

public class NestedClass
{
    public string? Car1 { get; set; }
    public string? Car2 { get; set; }
    public string? Car3 { get; set; }
}

this is what I'd do we can see that height and the cars are nullable, and the json contains no height. it gets the value null after deserialization

eric bonitoOP•4mo ago

Right that is the forward process but I am exploring this backwards thing with a json schema

Pobiega•4mo ago

I really can't see why or to what ends, but you do you 🙂

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✅ Json Validation and Populating with Nulls if Missing