Is it possible to deserialise a union schema disregarding the order of records?

[devantler]

Hey all! I have a use case where I need to deserialize Union schemas into their abstract models, but it only works if I reference a record below the current record.

For example, I can deserialize the following (backwards-reference):

[
    {
        "name": "RecordA",
        "type": "record",
        "fields": []
    },
    {
        "name": "RecordB",
        "type": "record",
        "fields": [
            {
                "name": "RecordA",
                "type": "RecordA"
            }
        ]
    }
]

But if I change the order of the records so that RecordB tries to reference RecordA when RecordB comes before RecordA, it will not work (forward-reference).

[
    {
        "name": "RecordB",
        "type": "record",
        "fields": [
            {
                "name": "RecordA",
                "type": "RecordA"
            }
        ]
    },
    {
        "name": "RecordA",
        "type": "record",
        "fields": []
    }
]

Can the JsonSchemaReader's deserialize functionality be extended to look for references in the whole file, not just the records before itself? I need the functionality, as I need it to deserialize models with circular references; I am using the library to generate EntityFramework entities, and ensuring my navigational properties work as expected is essential.

[dstelljes]

The behavior of the schema reader is actually defined by the spec:

A schema or protocol may not contain multiple definitions of a fullname. Further, a name must be defined before it is used (“before” in the depth-first, left-to-right traversal of the JSON parse tree, where the types attribute of a protocol is always deemed to come “before” the messages attribute.)

So, even though it looks counter-intuitive, the spec-compliant way to express that union would be:

[
    {
        "name": "RecordB",
        "type": "record",
        "fields": [
            {
                "name": "RecordA",
                "type": {
                    "name": "RecordA",
                    "type": "record",
                    "fields": []
                }
            }
        ]
    },
    "RecordA"
]

[devantler]

@dstelljes thank you so much! I overlooked that part and assumed the spec would follow a more flat approach. Your info here was very helpful, and I was able to update my test schema to work as expected:

[
    {
        "name": "Grade",
        "type": "enum",
        "symbols": [
            "A",
            "B",
            "C",
            "D",
            "F"
        ]
    },
    {
        "name": "Student",
        "type": "record",
        "fields": [
            {
                "name": "FirstMidName",
                "type": "string"
            },
            {
                "name": "LastName",
                "type": "string"
            },
            {
                "name": "EnrollmentDate",
                "type": "string"
            },
            {
                "name": "Enrollments",
                "type": {
                    "type": "array",
                    "items": {
                        "name": "Enrollment",
                        "type": "record",
                        "fields": [
                            {
                                "name": "Grade",
                                "type": "Grade"
                            },
                            {
                                "name": "Course",
                                "type": {
                                    "name": "Course",
                                    "type": "record",
                                    "fields": [
                                        {
                                            "name": "Title",
                                            "type": "string"
                                        },
                                        {
                                            "name": "Credits",
                                            "type": "int"
                                        },
                                        {
                                            "name": "Enrollments",
                                            "type": {
                                                "type": "array",
                                                "items": "Enrollment"
                                            }
                                        }
                                    ]
                                }
                            },
                            {
                                "name": "Student",
                                "type": "Student"
                            }
                        ]
                    }
                }
            }
        ]
    },
    "Enrollment",
    "Course"
]