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Converter that uses generics to parse json model

I have a converter class that receives json in input, here are 2 valid examples:
{
"method": "Model",
"payload": {
"key": "value"
}
}
and
{
"method": "OtherModel",
"payload": {
"foo": "bar"
}
}
In C#, I have classes mapped to each possible model:
public class Model
{
public string Key { get; set; }
}
public class OtherModel
{
public string Foo { get; set; }
}
I need a generic converter
How can I use the string value in the method of the JSON to convert in a generic way the content of the payload field?
Is using a huge switch the only way? This is the prototype I have so far but there are hundreds of different models so it will grow quite large...
public IResult ParseJson(string json)
{
Regex regexMessageName = new Regex("\"messageName\": \"(.*?)\"", RegexOptions.Compiled);
var messageName = regexMessageName.Match(json).Groups[1].Value;
switch (messageName)
{
case "Model":
var raw = JsonConvert.DeserializeObject<JsonData<Model>>(json);
return new LogInfoRequestResult<Model> { Raw = raw };
case "OtherModel":
var raw = JsonConvert.DeserializeObject<JsonData<OtherModel>>(json);
return new LogInfoRequestResult<OtherModel> { Raw = raw };
}
}

If you want complete control of your classes, and allow them to evolve independently, then you can have one base class that owns the Method, and then as many subclasses as you want with their own definition of the payload.
First, parse into the baseclass, just to get a strongly typed deserialization of Method
Then, there are a lot of patterns to address branching logic.
If you have 1-2 cases, an if statement is fine
If you have 3-5 cases, you can use a switch
If you have 6-10 cases, you can create a dictionary that maps method name to class type
If you have more than that, you can use the strategy pattern and pass an interface around
Here's an example of how you could write the code:
var json = #"{
'method': 'Model',
'payload': {
'key': 'value'
}
}";
var modelBase = JsonConvert.DeserializeObject<ModelBase>(json);
var methodMapping = new Dictionary<string, Type>()
{
{MethodTypes.Model.ToString(), typeof(Model)},
{MethodTypes.OtherModel.ToString(), typeof(OtherModel)},
};
Type methodClass = methodMapping[modelBase.Method];
var result = JsonConvert.DeserializeObject(json, methodClass);
Note: Since we're programmatically determining the correct type, it's hard to pass to a generic <T>, so this uses the overload of DeserializeObject that takes type as a param
And here are the classes that model incoming messages
public enum MethodTypes
{
Model,
OtherModel
}
public class ModelBase
{
public string Method { get; set; }
}
public class Model : ModelBase
{
public ModelInfo Payload { get; set; }
public class ModelInfo
{
public string Key { get; set; }
}
}
public class OtherModel : ModelBase
{
public ModelInfo Payload { get; set; }
public class ModelInfo
{
public string Foo { get; set; }
}
}
Dictionary<string,string>
If your data is always going to be "foo":"bar" or "key":"value" .... string:string, then Cid's suggesting to use Dictionary<string,string> Payload makes a lot of sense. Then figure out however you want to map from that c# class in a c# constructor that returns whatever type you want.
Additional Resources:
How to handle both a single item and an array for the same property using JSON.net
Deserializing polymorphic json classes without type information using json.net
JSON.NET - Conditional Type Deserialization
Conditionally deserialize JSON string or array property to C# object using JSON.NET?

You can instanciate an object of the expected class using Activator.CreateInstance(), then populate it with JsonConvert.PopulateObject()
In example :
Type t = Type.GetType($"NameSpaceName.{messageName}"); // this must be a fully qualified name
object obj = Activator.CreateInstance(t);
JsonConvert.PopulateObject(json, obj);

Generic class to store variable content

I want to create a structure to store data consumed from a Web Service with the followind specs:
Response:
Field 1 - InstructionType: Can be 1 (PreferredDay), 2 (SVP), 3 (Neighbour)
Field 2: Some variable data. Its type depends on Field 1. So if:
Field 1 == 1 then Field 2 type will be of DateTime (dd.MM.yyyy)
Field 1 == 2 then Field 2 type will be of type string.
Field 1 == 3 then Field 2 type will be of type string
So, I started up with the following enum:
public enum InstructionType
{
None = 0,
PreferredDay = 1,
ServicePoint = 2,
Neighbour = 3
}
And the generic class:
public abstract class Instruction<T>
{
public InstructionType Type { get; private set; }
public T Data { get; private set; }
public Instruction(InstructionType type, T data)
{
this.Type = type;
this.Data = data;
}
}
and concrete classes:
public class PreferredDayInstruction : Instruction<DateTime>
{
public PreferredDayInstruction(DateTime data)
: base (InstructionType.PreferredDay, data) {}
}
public class ServicePointInstruction: Instruction<string>
{
public ServicePointInstruction(string data)
: base (InstructionType.ServicePoint, data) {}
}
public class NeughbourInstruction: Instruction<string>
{
public NeughbourInstruction(string data)
: base (InstructionType.Neighbour, data) {}
}
When parsing web service's response created a public function:
public Instruction DeliveryInstruction() <---Compiler error here "Instruction"
{
if (resultFromWebservice.Field1 == 1)
return new PreferredDayInstruction((DateTime)Field2);
if (resultFromWebservice.Field1 == 2)
return new ServicePointInstruction(Field2);
if (resultFromWebservice.Field1 == 3)
return new NeighbourInstruction(Field2);
}
and here is the problem. Can't return objects of generic type.
Tried with with Interface, factories, and other stuff, but allways with the same problem. So, is there any way to archieve this? maybe it's not possible or maybe is so easy I can't see now. Thanks in advance.
UPDATE:
Compiler error on BOLD Instruction
Error 1 Using the generic type 'NAMESPACE.Instruction' requires '1' type arguments
I forgot..I'm using .NET 3.5

It looks like you may be starting off with an intent to use generics rather than using them because you've identified a need. Often (not always) when that gets difficult it's because it didn't actually fit what you were trying to do.
What seems odd in this case is that you have both a generic type and an enum to indicate the type. This is likely to cause you a few problems.
First it looks like you're trying to create a one-size-fits all class to model different types of behaviors. That will start off confusing and get more confusing. Think of most classes that are part of the .NET framework, and imagine what would happen if they had properties like Field1 and Field2, and you couldn't tell from looking at them what they were for. And in one method they're used for one thing, but in a another case they mean something else.
Also, if you're trying to put different types of instructions in one class, that suggests that maybe you're going to try passing them all to one method, and that method figures out what to do, and maybe calls other methods. (I'm guessing that because of the enum. Perhaps you're going to handle the input differently depending on which value it contains.) That one method will get really hard to maintain.
I'd recommend waiting on generics until you're sure you need them. And if you have different types of instructions you're likely better off writing a different class for each one with the properties it needs and names that describe them, and writing methods for each of them to do what they need to do. If you need lots of classes, make lots of them.
It's very easy to fall into the trap of trying to solve problems that don't exist, like how do I write one class that covers a bunch of different needs. The answer usually that you don't need to. You'll get better results from writing more classes that each do fewer things.

Believe me that I tried to do my best to explain what was my problem and what I needed in order to solve it. In a nutshell, the question was quite simple. Is this possible or not? So, is there a way to return a common type for these 3 classes? Answer is no, as they don't share any root. They all derive from Instruction, but aren't compatible each other. That's what I learned from this experience.
As another example, lets take another .NET framework's generic type.
public class ListOfString : List<string> { }
public class ListOfInt : List<int> { }
public class ListOfDecimal : List<decimal> { }
And, in another place of the application, get a method who returns one of this List based on some logic:
public class Logic
{
public List<> GetList(Type t) <----This can't be done
{
if (t == typeof(string))
return new ListOfString();
if (t == typeof(int))
return new ListOfInt();
if (t == typeof(decimal))
return new ListOfDecimal();
else return null;
}
}
Please, keep in mind that this is just a stupid sample just to show what's the point of this post.
By the way, in the case of List the following can be done, because there is a non generic different version of IList:
public IList GetList(Type t)
{
....
}
But I can't think of a way to do this in my particular case.
Anyway, I finally followed another approach. I reallized that what I really wanted is to ensure Data property is valid. If it it's supposed to be a date there, ensure date is valid. Is it a string, ensure it has the right length or whatever rule it must follow.
So this is the final solution:
The enum:
public enum InstructionType
{
None = 0,
PreferredDay = 1,
ServicePoint = 2,
Neighbour = 3
}
The base class:
public abstract class Instruction
{
public InstructionType Type { get; private set; }
public string Data { get; private set; } <---Type String
public Instruction(InstructionType type, string data)
{
this.Type = type;
this.Data = IsValid(data) ? data : string.Empty;
}
public abstract bool IsValid(string data); <--the rule.
}
The concrete classes:
public class PreferredDayInstruction : Instruction
{
public PreferredDayInstruction(string date)
: base(InstructionType.PreferredDay, date) { }
public override bool IsValid(string data)
{
string[] formats = {"dd.MM.yyyy", "d.MM.yyyy",
"dd.MM.yy", "d.MM.yy"};
try
{
data = data.Replace('/', '.').Replace('-', '.');
var dateparts = data.Split('.');
DateTime date = new DateTime(Convert.ToInt32(dateparts[2]),
Convert.ToInt32(dateparts[1]),
Convert.ToInt32(dateparts[0]));
//DateTime.ParseExact(data, formats, null, System.Globalization.DateTimeStyles.AssumeLocal);
return true;
}
catch (Exception)
{
return false;
}
}
}
public class ServicePointInstruction : Instruction
{
public ServicePointInstruction(string data)
: base (InstructionType.ServicePoint, data) { }
public override bool IsValid(string data)
{
return ServicePointBarcodeValidator.Validate(data);
}
}
public class NeighbourInstruction : Instruction
{
public NeighbourInstruction(string data) :
base(InstructionType.Neighbour, data) { }
public override bool IsValid(string data)
{
return data.Length <= 70;
}
}
A factory class, who's responsability is to create and return the correct object based on the enum:
public static class DeliveryInstructionFactory
{
public static Instruction Create(int type, string data)
{
return Create((InstructionType)type, data);
}
public static Instruction Create(InstructionType type, string data)
{
switch (type)
{
case InstructionType.PreferredDay:
return new PreferredDayInstruction(data);
case InstructionType.ServicePoint:
return new ServicePointInstruction(data);
case InstructionType.Neighbour:
return new NeighbourInstruction(data);
default:
return null;
}
}
}
And finally, as now all of they share the same root, object can be created on webservice's response parser:
public Instruction DeliveryInstruction()
{
try
{
int instructionCode = int.Parse(observation.Substring(173,2));
string instructionData = observation.Substring(175, 10);
return DeliveryInstructionFactory.Create(instructionCode, instructionData); }
catch (Exception ex)
{
Log.Error("[ValidationBarcodeResponse] DeliveryInstructions aren't in the correct format", ex);
return null;
}
}
Hope this now fits on a Minimal, Complete, and Verifiable example

Amazon Dynamo DB Persistent ORM

I am trying to create a generic wrapper library(C#/.NET) for AWS DynamoDB which can act as DAL(Data Access Layer). The applications consuming this library will not be tightly coupled with AWS libraries as there is a possibility that it can be changed later.
The structure of methods to be exposed from wrapper class are
InsertItem< T>(object) , UpdateItem< T>(object) , DeleteItem< T>(id/object),
List< T> GetAll() , T GetByParameter< T>(Id).
I see that there are three approaches to consume AWS DynamoDB services using AWSSDK.
Approach (1) : Low level Access - convert model to aws hashmap input structure and invoke getItem()/putItem() .
Approach (2) : High Level Access using Document - convert model to aws document model and passing document object to aws.
Approach (3) : High Level Access using Persistence - Using attribute DynamoDBTable in model to map model to dynamoDb table and using linq operation to get/update table.
In approach(1) & (2), i find it difficult to map the model to dynamoDB table. In approach (3), I see that i need to include the DynamoDB attributes in model class in application which would make it tightly coupled.
Is there any way to create mapping in runtime in this cases or is there any other approach?
I also thought whether i can json serialize/deserialize the model and inset into dynamoDB(In this case there would be only 2 columns - id, json body for any model).
Please correct me if i am wrong or missing something.

What follows is the solution I'm moving forward with, minus some extraneous details. The biggest challenge is reading data of arbitrary types, since you can't easily tell just from the JSON.
In my solution, the consuming application that chooses the types to write also knows how to identify which type to deserialize to when reading. This is necessary because I need to return multiple logs of different types, so it makes more sense to return the JSON to the consumer and let them deal with it. If you want to contain this in the DAL, you could add a Type column in the DB and convert it using Reflection, though I think you'd still have issues returning data for multiple types in one call.
The interface we present for consumption has read/write methods (you can add whatever else you need). Note that writing allows specification of T, but reading requires the caller to deserialize, as mentioned above.
public interface IDataAccess
{
Task WriteAsync<T>(Log<T> log) where T : class, new();
Task<IEnumerable<LogDb>> GetLogsAsync(long id);
}
A LogDb class contains the Persistence attributes:
[DynamoDBTable("TableName")]
public class LogDb
{
[DynamoDBHashKey("Id")]
public long Id{ get; set; }
[DynamoDBProperty(AttributeName = "Data", Converter = typeof(JsonStringConverter))]
public string DataJson { get; set; }
}
A generic Log<T> class used for strongly-typed writing. The ToDb() method is called in the IDataAccess implementation to actually write to the DB. The constructor taking in a LogDb would be used by a consuming application that had identified the appropriate type for deserialization:
public class Log<T>
where T : class, new()
{
public Log() { }
public Log(LogDb logDb)
{
Data = licensingLogDb.OldDataJson.Deserialize<T>();
Id = licensingLogDb.Id;
}
public long Id { get; set; }
public T Data { get; set; }
public LogDb ToDb()
{
string dataJson = Data.Serialize();
return new LogDb
{
DataJson = dataJson,
Id = Id
};
}
}
The JsonStringConverter used in the attributes on LogDb converts the JSON string in the DataJson property to and from a DynamoDB Document:
public class JsonStringConverter : IPropertyConverter
{
public DynamoDBEntry ToEntry(object value)
{
string json = value as string;
return !String.IsNullOrEmpty(json)
? Document.FromJson(json)
: null;
}
public object FromEntry(DynamoDBEntry entry)
{
var document = entry.AsDocument();
return document.ToJson();
}
}
A helper class provides the Serialize and Deserialize extensions, which use JSON.NET's JsonConvert.Serialize/Deserialize, but with null checks:
public static class JsonHelper
{
public static string Serialize(this object value)
{
return value != null
? JsonConvert.SerializeObject(value)
: String.Empty;
}
public static T Deserialize<T>(this string json)
where T : class, new()
{
return !String.IsNullOrWhiteSpace(json)
? JsonConvert.DeserializeObject<T>(json)
: null;
}
}

Generic method convert Dynamo table to c# class as an extension function.
public static List<T> ToMap<T>(this List<Document> item)
{
List<T> model = (List<T>)Activator.CreateInstance(typeof(List<T>));
foreach (Document doc in item)
{
T m = (T)Activator.CreateInstance(typeof(T));
var propTypes = m.GetType();
foreach (var attribute in doc.GetAttributeNames())
{
var property = doc[attribute];
if (property is Primitive)
{
var properties = propTypes.GetProperty(attribute);
if (properties != null)
{
var value = (Primitive)property;
if (value.Type == DynamoDBEntryType.String)
{
properties.SetValue(m, Convert.ToString(value.AsPrimitive().Value));
}
else if (value.Type == DynamoDBEntryType.Numeric)
{
properties.SetValue(m, Convert.ToInt32(value.AsPrimitive().Value));
}
}
}
else if (property is DynamoDBBool)
{
var booleanProperty = propTypes.GetProperty(attribute);
if (booleanProperty != null)
booleanProperty.SetValue(m, property.AsBoolean());
}
}
model.Add(m);
}
return model;
}

Persisting dynamic object in DynamoDB with .NET SDK

I'm trying to persist the following class to DynamoDB using the .NET SDK:
public class MyClass
{
public string Id { get; set; }
public string Name { get; set; }
public object Settings { get; set; }
}
The problem is with the Settings property. It can be any type of object, and I do not know in advance what might be assigned to it. When I try to persist it to DynamoDB, I get the following exception:
System.InvalidOperationException: 'Type System.Object is unsupported, it has no supported members'
Both the Document Model and Object Persistence Model methods result in the same exception.
Is there a way to persist these objects in DynamoDB? Other databases like MongoDB and Azure DocumentDB will do this without any issue, and they can be deserialized to either the proper type with a discriminator, or as a dynamic JSON object.

You can use the general approach documented here: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBContext.ArbitraryDataMapping.html
Here's my implementation for any arbitrary object:
public class DataConverter : IPropertyConverter
{
public object FromEntry(DynamoDBEntry entry)
{
var primitive = entry as Primitive;
if (primitive == null || !(primitive.Value is String) || string.IsNullOrEmpty((string)primitive.Value))
throw new ArgumentOutOfRangeException();
object ret = JsonConvert.DeserializeObject(primitive.Value as string);
return ret;
}
public DynamoDBEntry ToEntry(object value)
{
var jsonString = JsonConvert.SerializeObject(value);
DynamoDBEntry ret = new Primitive(jsonString);
return ret;
}
}
Then annotate your property like this:
[DynamoDBProperty(typeof(DataConverter))]
public object data { get; set; }

Little improvement to the previous answer: make converter generic so that you can deserialize to the correct type, like this:
public class SerializeConverter<T> : IPropertyConverter
{
public object FromEntry(DynamoDBEntry entry)
{
var primitive = entry as Primitive;
if (primitive is not { Value: string value } || string.IsNullOrEmpty(value))
throw new ArgumentException("Data has no value", nameof(entry));
return JsonConvert.DeserializeObject<T>(value);
}
public DynamoDBEntry ToEntry(object value) =>
new Primitive(JsonConvert.SerializeObject(value));
}
Usage:
[DynamoDBProperty(typeof(SerializeConverter<YourType>))]
public YourType data{ get; set; }

I struggled to find a good solution for interacting with thoroughly unstructured data, then eventually realized that the DynamoDBContext really isn't designed for that.
For anyone else who gets to this point, my advice is to drop to a lower abstraction level and use the AmazonDynamoDBClient directly with Dictionary<string, AttributeValue> objects.

Using ServiceStack OrmLite to create Key Value table for dynamic types

I want to create a key value table in my database along the lines of
public class KeyValue {
public string Id { get; set; }
public dynamic Value {get; set; }
}
Using a slightly modified SqlProvider I have no problems getting CreateTable<KeyValue>() to generate varchar(1024) Id, varchar(max) Value.
I have no issues saving objects to it. The problem is when I load the objects
var content = dbConn.GetById<KeyValue>("about");
content.Value at this point is a string.
Looking at the database record, the text for value does not appear to store any type information.
Is there really anything I can do better other than manually invoking ServiceStack.Text and call deserialize with the appropriate type information?
I do not need absolute dynamic, my actual use case is for polymorphism with a base class instead of dynamic. So I don't really care what type Value is whether it's the base class, dynamic, object, etc. Regardless other than using the class
public class KeyValue {
public string Id { get; set; }
public MySpecificChildType Value {get; set; }
}
I haven't been able to get anything other than a string back for Value. Can I tell OrmLite to serialize the type information to be able to correctly deserialize my objects or do I just have to do it manually?
Edit: some further information. OrmLite is using the Jsv serializer defined by ServiceStack.Text.TypeSerializer and is in no way pluggable in the BSD version. If I add a Type property to my KeyValue class with the dynamic Value I can do
var value = content.Value as string;
MySpecificChildType strongType =
TypeSerializer.DeserializeFromString(content, content.Type);
I just really want a better way to do this, I really don't like an object of 1 type going into the db coming back out with a different type (string).

I haven't worked much with the JsvSerializer but with the JsonSerializer you can achieve this (in a few different ways) and as of ServiceStack 4.0.11 you can opt to use the JsonSerializer instead, see https://github.com/ServiceStack/ServiceStack/blob/master/release-notes.md#v4011-release-notes.
Example
public abstract class BaseClass {
//Used for second example of custom type lookup
public abstract string Type { get; set; }
}
public class ChildA : BaseClass {
//Used for second example of custom type lookup
public override string Type { get; set; }
public string PropA { get; set; }
}
And then in your init/bootstrap class you can configure the serializer to emit the type information needed for proper deserialization:
public class Bootstrapper {
public void Init() {
ServiceStack.Text.JsConfig.ExcludeTypeInfo = false;
ServiceStack.Text.JsConfig.IncludeTypeInfo = true;
}
}
If you wish to use something other that the default "__type" attribute that ServiceStack uses (if you for example want to have a friendly name identifying the type rather then namespace/assembly) you can also configure your own custom type lookup as such
public class Bootstrapper {
public void Init() {
ServiceStack.Text.JsConfig.ExcludeTypeInfo = false;
ServiceStack.Text.JsConfig.IncludeTypeInfo = true;
ServiceStack.Text.JsConfig.TypeAttr = "type";
ServiceStack.Text.JsConfig.TypeFinder = type =>
{
if ("CustomTypeName".Equals(type, StringComparison.OrdinalIgnoreCase))
{
return typeof(ChildA);
}
return typeof(BaseClass);
}
}
}