القيود والقيم الافتراضية والتعدادات

Types say what kind of value is allowed, but you often want tighter rules: a limit must be positive, a name not empty. That's where constraints come in.

Pydantic's Field lets you attach rules to a field, like minimum and maximum values, right in the model definition.

Use ge and le for greater-or-equal and less-or-equal, or gt and lt for strict bounds, to keep numbers in a safe range.

For text, min_length and max_length stop empty strings and runaway input before they reach your logic.

Add a pattern to require a string match a regular expression, perfect for codes, slugs, or simple identifiers.

Give a field a value and it becomes optional with a default. The model may omit it and your tool uses the fallback.

You can combine a default with constraints by passing it to Field, keeping the rule and the fallback in one place.

When only a few values make sense, an Enum limits the field to that exact set, so the model cannot invent options.

Declare a field with the enum type and Pydantic accepts only its members, rejecting any other value automatically.

For a quick fixed set you can also use Literal, which lists allowed values inline without a separate Enum class.

These rules become part of the JSON schema, so the model sees the allowed ranges and choices and tends to obey them.

You want a field to accept only asc or desc. What fits best?

Use Field for bounds and lengths, plain defaults for optional values, and Enum or Literal for fixed choices the model must respect. ✅