Is it possible define tuples instead of lists for types?

[nbro10]

I have a json schema like this

{
    "type": "object",
    "description": "My desc",
    "properties": {
        "x": {
            "$ref": "./A.json#"
        },
        "y": {
            "type": "array",
            "minItems": 2,
            "maxItems": 2,
            "items": [
                {
                    "$ref": "./B.json#"
                },
                {
                    "oneOf": [
                        {
                            "$ref": "./C.json#"
                        },
                        {
                            "$ref": "./D.json#"
                        }
                    ]
                }
            ]
        }
    },
    "required": [
        "x",
        "y"
    ],
    "additionalProperties": false
}

This generates a Pydantic V2 model like this (or something like this)

class Model(BaseModel):
    """
    My Desc
    """

    model_config = ConfigDict(
        extra="forbid",
    )
    x: A
    y: list[B | C| D] = Field(
        ..., max_length=2, min_length=2
    )

But what I want is that y is a tuple, where the first element is of type B and the second element can be C or D. So, I want this

class Model(BaseModel):
    """
    My Desc
    """

    model_config = ConfigDict(
        extra="forbid",
    )
    x: A
   y: tuple[B, C | D] = Field(
        ..., max_length=2, min_length=2
    )

In other words, the first element should always be a B, while the second can be a C or D. In reality, I don't really care if this is a tuple, it could also be a list, as long as the type constraints of the elements I've just described is satisfied.

I don't know if this is a JSON schema limitation or not.

I thought of overriding the template, but maybe there's an easier solution just by changing my schema to specify that?

Also, I don't really know right now how I'd need to override the template.

[nbro10]

So, my understanding is that this should be possible with prefixItems, but this library still doesn't support this feature: #1546. In fact, if I manually change the list type to the tuple I want and use Pydantic to generate the schema, it generates a schema like mine except that it uses prefixItems instead of items.

[nbro10]

So, prefixItems was added only in JSON schema draft 2020. I don't know which versions of JSON schema datamodel-code-generator supports. There are other tools like hypothesis-schema that don't support 2020. It's a pity because these versions have been around for 4 years (I suppose).

However, according to https://github.com/orgs/json-schema-org/discussions/535#discussioncomment-7613705, I think we don't strictly need prefixItems to specify that each item in the array has a different type or subschema.

So, I think that datamodel-code-generator should provide a flag that replaces lists with tuples at least in specific cases, like when the min and max number of elements in the array are equal and we're using different types or schemas for the elements. In that case, we most likely want to use tuples instead of lists.