Conditionally [jsonignore]

Preface

Usually , It's going on JSON When serializing or deserializing , If you want to ignore an attribute , We will use [JsonIgnore] characteristic ：

public class User
{
    public int Id { get; set; }
    [JsonIgnore]
    public string Name { get; set; }
}

var user = new User { Id = 1, Name = "MyIO" };
Console.WriteLine(JsonSerializer.Serialize(user));

// Output 
{"Id":1}

By chance , [JsonIgnore] Properties can also be specified Condition attribute :

[JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
public string Name { get; set; }

So what does it do ？

JsonIgnoreCondition enumeration

Can be set by [JsonIgnore] Characteristic Condition Property to specify the conditional exclusion .Condition Property corresponds to  JsonIgnoreCondition Enumeration provides the following options ：

• Always - Always ignore attributes . If not specified Condition, This option defaults

• Never - Ignore global settings , Always serialize and deserialize attributes

public class A
{
    public string Name { get; } = "MyIO";
}

public class B
{
    [JsonIgnore( Condition = JsonIgnoreCondition.Never)]
    public string Name { get; } = "MyIO";
}

// Global setting to ignore read-only properties 
var options = new JsonSerializerOptions
{
    IgnoreReadOnlyProperties = true
};

Console.WriteLine(JsonSerializer.Serialize(new A(), options));
Console.WriteLine(JsonSerializer.Serialize(new B(), options));

// Output 
//A  Medium  Name  No serialization , and  B  Medium  Name  Still serialize 
{}
{"Name":"B"}

• WhenWritingDefault - If the attribute value is the default value of the attribute data type , Then ignore the attribute in the serialization

public class User
{
    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingDefault)]
    public int Id { get; set; }

    public string Name { get; set; }
}

var user = new User { Id = 0, Name = "" };
Console.WriteLine(JsonSerializer.Serialize(user));

// Output 
{"Name":""}

• WhenWritingNull - If the property value is null, Then ignore the attribute in the serialization

public class User
{

    public int Id { get; set; }

    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
    public string Name { get; set; }
}

var user = new User { Id = 1, Name = null };
Console.WriteLine(JsonSerializer.Serialize(user));

// Output 
{"Id":1}

Conclusion

We can also use JsonSerializerOptions Set the way to ignore properties globally ：

• DefaultIgnoreCondition - default JsonIgnoreCondition, The default value is Never

• IgnoreReadOnlyProperties - Ignore all read-only properties

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