Return computed json as simple as possible

[gbanusi]

Hi,

I have a computed with FilterBy method. I need to return a JSON of an object referencing other objects:

Computed Countries 'repository => { return ...; }'
{
        ShortString entity;
        Object Entity 'Module.Entity';

        FilterBy CountriesLastModifiedTime '(repository, parameter) =>
        {
          return repository.Module.Entity.Query().
                Select(x =>  new 
                    {
                        ID = x.ID,
                        ...
                        Entity= x.Entity,
                    }
                ).ToArray().Select(x => new Countries()
                    {
                        ID = x.ID,
                        ...
                        Entity= x.Entity!= null ? x.Entity.ToSimple() : null,
                }).ToArray();
        }';
}

Is there any possibility to avoid selecting twice? What is the best approach?

This is an example how the json should look like:

[bantolov]

Hi, What result do you get if you simply remove the first Select and ToSimple()? Are there any errors? For example:

FilterBy CountriesLastModifiedTime '(repository, parameter) =>
{
    return repository.Module.Entity.Query()
        .Select(x => new Countries()
            {
                ID = x.ID,
                ...
                Entity= x.Entity
        }).ToArray();
}';

I have tried to reproduce a similar setup with entities Comment and Book, from Bookstore - Book.rhe. The query seems to work, at least in the LinqPad script:

class PrincipalHasRoleDTO
{
    public Guid ID { get; set; }
    public string Text { get; set; }
    public Bookstore.Book Book { get; set; }
}
...
var data = repository.Bookstore.Comment.Query()
    .Select(comment => new PrincipalHasRoleDTO
    {
        ID = comment.ID,
        Text = comment.Text,
        Book = comment.Book
    })
    .ToArray();

// Trying to simulate the web response:
JsonConvert.SerializeObject(data, Newtonsoft.Json.Formatting.Indented).Dump();

Result:

[
  {
    "ID": "259c6719-d20c-4b76-a2b5-0b24a432391e",
    "Text": "b",
    "Book": {
      "Code": "123",
      "Active": null,
      "AuthorID": "0c61ca43-03ad-4208-a328-ef6cd766745c",
      "NumberOfPages": 123,
      "Price": null,
      "Title": "123",
      "ID": "9b1dd9c7-6e78-4ea0-a24c-9e812a8c15d5"
    }
  },
  {
    "ID": "ce736146-556a-41c8-83e3-23a9e5b3d349",
    "Text": "a",
    "Book": {
      "Code": "123",
      "Active": null,
      "AuthorID": "0c61ca43-03ad-4208-a328-ef6cd766745c",
      "NumberOfPages": 123,
      "Price": null,
      "Title": "123",
      "ID": "9b1dd9c7-6e78-4ea0-a24c-9e812a8c15d5"
    }
  }
]

[gbanusi]

When I try it like you did I get the following:

2019-09-19 17:30:27.3582|ERROR|GlobalErrorHandler|System.Runtime.Serialization.SerializationException: Type 'System.Data.Entity.DynamicProxies.MasterData_ForeignCu_396E705A5D066358B9CC0FF8B3038BA3DD6A41ED30BEA1473A2CD05805515881' with data contract name 'MasterData_ForeignCu_396E705A5D066358B9CC0FF8B3038BA3DD6A41ED30BEA1473A2CD05805515881:http://schemas.datacontract.org/2004/07/System.Data.Entity.DynamicProxies' is not expected. Consider using a DataContractResolver if you are using DataContractSerializer or add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to the serializer.

[bantolov]

The SerializationException is caused by WCF's JSON serializer having issues with Entity Framework's proxy classes. This is why my test worked well with Newtonsoft's serializer, but web response fails.

Your code example (two Select methods) is a good workaround that helps to simplify the data types for the serializer.

I'll try to find a cleaner solution for this example and post the results here.

[bantolov]

I have done some research, this problem is a combination of several factors:

• DataContractJsonSerializer (WCF's JSON serializer) tries to serialize the complete instance type (queryable or proxy class), while we just want to serialize the declared (simple) type.
• Entity Framework creates proxy classes that are difficult to register as known types to the serializer. The proxy classes may be suppressed, but then we loose lazy loading feature.

This whole issue might be solved automatically after we move away from WCF to ASP.NET Core and use a different JSON serializer. In the meantime, you could modify the generated DTO class to provide a customized serialization for the complex properties, that will avoid the issues above.

You can find the complete solution in this commit on Bookstore repository.

1. It contains a custom concept: ComplexProperty, that fixes this issue with an alternative property for serialization.
   • Modify your implementation of Object concept to do the same, or use ComplexProperty instead.
2. DSL script DTO.rhe provides an example of using this concept, with web response similar to the one described in the question.