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Pydantic & SQLAlchemy

Pydantic v2 and SQLAlchemy 2.x: data validation, serialization, ORM declarative mapping, async sessions, relationship loading strategies, Alembic migrations, and production patterns for Python backends.

Pydantic & SQLAlchemy

What is Pydantic's BaseModel?

Using Field() for metadata and constraints

Nested Pydantic models

model_dump() and model_dump_json()

Pydantic v1 vs v2 key differences

SQLAlchemy Core vs ORM

Declarative mapping with Mapped[] and mapped_column()

@field_validator in Pydantic v2

@model_validator for cross-field validation

model_config and ConfigDict

Computed fields and @computed_field

Discriminated unions in Pydantic v2

pydantic-settings for configuration management

Session and the Unit of Work pattern

Lazy vs eager loading — selectinload and joinedload

Async sessions with AsyncSession

Custom Pydantic v2 types with __get_pydantic_core_schema__

TypeAdapter for validating non-model types

Diagnosing and fixing the N+1 problem

Alembic migrations with SQLAlchemy 2.x

Hybrid properties and SQL expressions

Connection pooling and async pool configuration

SQLAlchemy events and the event system

Integrating Pydantic v2 with SQLAlchemy 2.x