GraphQL type mappings break when using class prefixes

[siminn-arnorgj]

Describe the bug

When using the --class-name-prefix option with GraphQL, the default scalar type mappings (and custom mappings) break, resulting in incorrect types in the generated models.

To Reproduce

type Apple {
  color: String!
  ripe: Boolean!
}

type Orange {
  size: Float!
  count: Int!
}

Used commandline:

$ datamodel-codegen --input ./apples.graphql --input-file-type graphql --class-name-prefix ABC

Current behavior

from __future__ import annotations

from typing import Literal, TypeAlias

from pydantic import BaseModel, Field

ABCBoolean: TypeAlias = str
"""
The `Boolean` scalar type represents `true` or `false`.
"""


ABCFloat: TypeAlias = str
"""
The `Float` scalar type represents signed double-precision fractional values as specified by [IEEE 754](https://en.wikipedia.org/wiki/IEEE_floating_point).
"""


ABCInt: TypeAlias = str
"""
The `Int` scalar type represents non-fractional signed whole numeric values. Int can represent values between -(2^31) and 2^31 - 1.
"""


ABCString: TypeAlias = str
"""
The `String` scalar type represents textual data, represented as UTF-8 character sequences. The String type is most often used by GraphQL to represent free-form human-readable text.
"""


class ABCApple(BaseModel):
    color: ABCString
    ripe: ABCBoolean
    typename__: Literal['Apple'] | None = Field('Apple', alias='__typename')


class ABCOrange(BaseModel):
    count: ABCInt
    size: ABCFloat
    typename__: Literal['Orange'] | None = Field('Orange', alias='__typename')

Expected behavior

The generated types for ABCBoolean, ABCFloat, and ABCInt should map to the correct Python types (bool, float, and int respectively) instead of all mapping to str.

Version:

• OS: MacOS 26.2
• Python version: 3.13.9
• datamodel-code-generator version: 58e73ed

[github-actions]

🎉 Released in 0.52.2

The fix/feature from PR #2926 has been included in this release. See the release notes for details.

Thank you for your contribution!