Body — Fields

Using Field()

Use Field() to add metadata and constraints to Pydantic model fields:

from pydantic import BaseModel, Field
from typing import Optional
from justapi import JustAPIApp

class Item(BaseModel):
    name: str = Field(..., min_length=1, max_length=100)
    price: float = Field(..., gt=0)
    description: Optional[str] = Field(None, max_length=500)
    tags: list[str] = Field(default_factory=list)

app = JustAPIApp()

@app.post("/items")
def create_item(item: Item):
    return item.model_dump()

Field Options

Option	Type	Description
`default`	`Any`	Default value
`alias`	`str`	Alternative field name
`title`	`str`	Title in OpenAPI docs
`description`	`str`	Description in OpenAPI docs
`examples`	`list`	Example values
`min_length`	`int`	Minimum string length
`max_length`	`int`	Maximum string length
`gt`	`Number`	Greater than
`ge`	`Number`	Greater than or equal
`lt`	`Number`	Less than
`le`	`Number`	Less than or equal
`pattern`	`str`	Regex pattern

Examples

class CreateUser(BaseModel):
    username: str = Field(
        ...,
        min_length=3,
        max_length=50,
        pattern=r"^[a-zA-Z0-9_]+$",
        title="Username",
        description="Alphanumeric characters and underscores only",
        examples=["alice_123"],
    )
    email: str = Field(
        ...,
        pattern=r"^[\w.-]+@[\w.-]+\.\w+$",
        title="Email address",
    )
    age: int = Field(
        ...,
        ge=13,
        le=120,
        title="Age",
        description="Must be between 13 and 120",
    )

See Also

Schema & Validation — validation reference
Body — Multiple Parameters — multiple body params
Body — Nested Models — nested models