Strategies: tweak how fields are generated

Modify policies and providers per field without rewriting emitters.

Strategy builder overview

• StrategyBuilder inspects model fields, summarises constraints, and assigns providers.
• Union fields become UnionStrategy instances with multiple choices and a policy (first, random, or weighted).
• Optional fields inherit p_none probabilities from configuration or presets.
• Enum fields use the enum.static provider by default.

Modify strategies with plugins

Implement pfg_modify_strategy to adjust probabilities or swap providers.

# plugins/nickname_strategy.py

from pydantic import BaseModel

from pydantic_fixturegen.plugins.hookspecs import hookimpl

class NicknameTweaks:

    @hookimpl

    def pfg_modify_strategy(self, model: type[BaseModel], field_name: str, strategy):

        if model.__name__ == "User" and field_name == "nickname":

            return strategy.model_copy(update={"p_none": 0.1})

        return None

plugin = NicknameTweaks()

• Return a new Strategy to override attributes; return None to keep the original.
• Use model_copy (dataclass copy) to avoid mutating shared state.
• Register the plugin via entry points or manual registry registration (see providers).

Common adjustments

• Increase p_none for optional fields that should appear sparingly.
• Swap providers by updating provider_ref/provider_name to point at custom implementations.
• Override enum_policy to random when exploring edge cases.
• Alter provider_kwargs to tune providers that accept additional parameters.

Validate your changes

• Run pfg gen explain --tree to confirm new strategies appear in the output.
• Combine with --preset boundary to ensure presets and custom strategies interact correctly.
• Use pfg doctor to verify no coverage gaps remain after replacing providers.

Strategies work hand-in-hand with emitters, which consume provider output to write artifacts.