What I'm trying to do may look odd at first, but I'll explain why I'm trying to achieve that then.
In my Domain layer I created a constants class where I define all my AWS DynamoDB database structure to be used like a sort of Enum wherever I need database tables and fields names.
DBStructure.cs:
public class DBStructure
{
public struct DynamoDB
{
public struct Tables
{
public struct Tests
{
public const string TableName = "test_test";
public struct Fields
{
[JsonProperty("DynamoDB")]
public const string TestId = "test_id";
public const string Test = "test";
public const string TestLevel = "test_level";
public const string TestNumber = "test_level_number";
public const string TestType = "test_type";
public const string TestSubject = "test_subject";
public const string FP = "f_p";
public const string PermittedErrors = "permitted_errors";
public const string TimeLimit = "time_limit";
public const string TestCreator = "test_author";
public const string TestCreatorEmail = "email";
public const string Active = "active";
public const string TestComments = "comments";
public const string TestImage = "image";
public const string TestLanguage = "language_id";
public const string TestLanguage2 = "test_lng";
public const string TestLanguage3 = "test_language";
public const string TestTimestamp = "timestamp";
}
public struct Indexes
{
public const string TestTypeIndex = "test_type-index";
public const string TestSubjectIndex = "test_subject-index";
}
}
public struct Questions
{
public const string TableName = "test_questions";
public struct Fields
{
public const string QuestionId = "question_id";
public const string TestId = "test_id";
public const string Instructions = "instructions";
public const string Question = "question";
public const string Explanations = "explanations";
public const string QuestionNumber = "question_number";
public const string Timestamp = "timestamp";
}
public struct Indexes
{
public const string TestIdQuestionNumberIndex = "test_id-question_number-index";
}
}
... More Structs
}
}
}
I need to serialize this complete class in order to be able to pass the string consts to Javascript through an Ajax call.
The reason for that is because I need the fields -and tables- names as in Javascript, when the Test is to be saved, I create a json with its data (read from html form fields) to be sent to the controller.
I definitely know this is not the way (or at least not the best one) to accomplish this, but I'm in the middle of a big refactor and just going step by step.
I've tried Is serialization possible for a struct, but the problem is that in my case the members are constants, and so it's not working.
Any way to accomplish my class serialization? Any comments are welcome.
Thanks to: Serialize a const with System.Text.Json.Serialization
I was able to sort my issue using the provided JsonExtensions class.
JsonExtensions:
public static partial class JsonExtensions
{
// Include opted-in constants for the specified type.
public static Action<JsonTypeInfo> AddOptInConstMembers<TOptInAttribute>(Type type) where TOptInAttribute : System.Attribute =>
typeInfo =>
{
if (typeInfo.Type == type)
AddOptInConstMembers<TOptInAttribute>(typeInfo);
};
// Include opted-in constants for all types.
public static void AddOptInConstMembers<TOptInAttribute>(JsonTypeInfo typeInfo) where TOptInAttribute : System.Attribute
{
if (typeInfo.Kind != JsonTypeInfoKind.Object)
return;
foreach (var field in typeInfo.Type.GetConstants().Where(f => Attribute.IsDefined(f, typeof(TOptInAttribute))))
{
var name = field.GetCustomAttribute<JsonPropertyNameAttribute>()?.Name ?? typeInfo.Options.PropertyNamingPolicy?.ConvertName(field.Name) ?? field.Name;
var value = field.GetValue(null); // field.GetValue(null); returns enums as enums rathen raw integers.
var propertyInfo = typeInfo.CreateJsonPropertyInfo(value?.GetType() ?? field.FieldType, name);
propertyInfo.Get = (o) => value;
propertyInfo.CustomConverter = field.GetCustomAttribute<JsonConverterAttribute>()?.ConverterType is { } converterType
? (JsonConverter?)Activator.CreateInstance(converterType)
: null;
typeInfo.Properties.Add(propertyInfo);
}
}
static IEnumerable<FieldInfo> GetConstants(this Type type) =>
// From the answer https://stackoverflow.com/a/10261848
// By https://stackoverflow.com/users/601179/gdoron
// To https://stackoverflow.com/questions/10261824/how-can-i-get-all-constants-of-a-type-by-reflection
type.GetFields(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.FlattenHierarchy)
.Where(fi => fi.IsLiteral && !fi.IsInitOnly);
}
Then in my code:
public class DBStructure
{
public struct DynamoDB
{
public struct Tables
{
public struct Tests
{
public const string TableName = "test_test";
public struct Fields
{
[JsonInclude]
public const string TestId = "test_id";
[JsonInclude]
public const string Test = "test";
[JsonInclude]
public const string TestLevel = "test_level";
...
}
}
public struct Questions
{
public const string TableName = "test_questions";
public struct Fields
{
[JsonInclude]
public const string QuestionId = "question_id";
[JsonInclude]
public const string TestId = "test_id";
...
}
}
... More Structs
}
}
}
And I use it more or less like this (still need to adjust it a little bit in order to return an object with all json, but I'm close to what I expect):
var testsFiels = new DBStructure.DynamoDB.Tables.Tests.Fields();
var questionsFiels = new DBStructure.DynamoDB.Tables.Questions.Fields();
var options = new JsonSerializerOptions
{
TypeInfoResolver = new DefaultJsonTypeInfoResolver
{
Modifiers = { JsonExtensions.AddOptInConstMembers<JsonIncludeAttribute> },
},
};
var testsJson = System.Text.Json.JsonSerializer.Serialize(testsFiels, options);
var questionsJson = System.Text.Json.JsonSerializer.Serialize(questionsFiels, options);