Data Validation Examples

Complete examples for Pydantic v2 validation, database schema alignment, and data quality monitoring.

Examples Overview

User Validation Example

File: user-validation-example.md

Complete user validation workflow with:

Pydantic v2 model with field validators
Email, username, age validation
Cross-field validation (admin age requirement)
SQLModel database alignment
FastAPI integration
Validation error formatting
Pytest test suite

Use when: Building user registration, profile management, or authentication.

Order Validation Example

File: order-validation-example.md

Complex order validation with:

Nested object validation (order items, shipping address)
Currency and pricing validation
Inventory quantity checks
Multi-tenant validation (tenant_id)
Custom validators for business rules
Database transaction validation

Use when: Building e-commerce, order management, or invoicing systems.

Nested Validation Example

File: nested-validation.md

Advanced nested validation patterns:

Nested Pydantic models
List validation with min/max items
Discriminated unions for polymorphic data
Recursive validation (tree structures)
Forward references
Validation context passing

Use when: Working with complex JSON structures, API payloads, or hierarchical data.

Quick Reference

Example	Complexity	Key Patterns
User	Basic	Field validators, cross-field validation
Order	Intermediate	Nested objects, business rules, transactions
Nested	Advanced	Discriminated unions, recursion, context

Common Patterns

Basic Validation

from pydantic import BaseModel, Field, EmailStr

class User(BaseModel):
    email: EmailStr
    age: int = Field(ge=13, le=120)

Field Validator

from pydantic import field_validator

class User(BaseModel):
    username: str

    @field_validator('username')
    @classmethod
    def validate_username(cls, v: str) -> str:
        if len(v) < 3:
            raise ValueError('Username too short')
        return v

Model Validator

from pydantic import model_validator

class User(BaseModel):
    role: str
    age: int

    @model_validator(mode='after')
    def check_admin_age(self):
        if self.role == 'admin' and self.age < 18:
            raise ValueError('Admins must be 18+')
        return self

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