DocsSQL databases

Use PostgreSQL with Nexy

To use PostgreSQL with Nexy, install the psycopg driver, set DATABASE_URL to a postgresql+psycopg:// URL, and query it from handlers and pages through SQLModel or SQLAlchemy.

Run PostgreSQL locally

docker run --name nexy-db -e POSTGRES_PASSWORD=secret -e POSTGRES_DB=app -p 5432:5432 -d postgres:17

Install the driver

uv add "psycopg[binary]"

psycopg is version 3 of the driver, for sync and async code. For async-only code, asyncpg is the other choice:

uv add asyncpg

The connection string

.env

DATABASE_URL=postgresql+psycopg://postgres:secret@localhost:5432/app

URL	Driver
`postgresql+psycopg://user:pass@host:5432/db`	psycopg 3, sync and async
`postgresql+asyncpg://user:pass@host:5432/db`	asyncpg, async only
`postgresql://user:pass@host:5432/db`	psycopg2, if it is installed
`postgres://...`	rejected by SQLAlchemy: rename the scheme to `postgresql+psycopg://`

A password with @, : or / in it is percent-encoded in the URL: p@ss is p%40ss.

The engine

Hosting platforms often hand out a postgres:// URL. Convert it where the engine is made:

src/configs/db.py

import os from dotenv import load_dotenvfrom sqlmodel import create_engine load_dotenv()  def database_url() -> str:    url = os.environ["DATABASE_URL"]    return url.replace("postgres://", "postgresql+psycopg://", 1)  engine = create_engine(database_url(), pool_size=5, max_overflow=10, pool_pre_ping=True)

Pool option	What it does
`pool_size=5`	connections kept open per process
`max_overflow=10`	extra connections allowed under load, closed after
`pool_pre_ping=True`	checks a connection before use, so a restarted database is no error

Each nx start worker has its own pool: workers × (pool_size + max_overflow) must stay under the server's max_connections.

A model with PostgreSQL types

uuid keys, JSONB, arrays and timestamptz are native column types:

src/models/post_model.py

import uuidfrom datetime import datetime, timezone from sqlalchemy import Column, DateTime, Stringfrom sqlalchemy.dialects.postgresql import ARRAY, JSONBfrom sqlmodel import Field, SQLModel  class Post(SQLModel, table=True):    id: uuid.UUID = Field(default_factory=uuid.uuid4, primary_key=True)    title: str = Field(max_length=200, index=True)    tags: list[str] = Field(default_factory=list, sa_column=Column(ARRAY(String)))    extra: dict = Field(default_factory=dict, sa_column=Column(JSONB))    published_at: datetime = Field(        default_factory=lambda: datetime.now(timezone.utc),        sa_column=Column(DateTime(timezone=True)),    )

A session per request

src/configs/session.py

from collections.abc import Iterator from sqlmodel import Session from src.configs.db import engine  def get_session() -> Iterator[Session]:    with Session(engine) as session:        yield session

Read and write from a handler

src/routes/api/posts/index.py

from pydantic import BaseModelfrom sqlmodel import Session, select from nexy.http import Depends, JSONResponsefrom src.configs.session import get_sessionfrom src.models.post_model import Post  class NewPost(BaseModel):    title: str    tags: list[str] = []  async def GET(tag: str | None = None, session: Session = Depends(get_session)):    query = select(Post).order_by(Post.published_at.desc())    if tag:        query = query.where(Post.tags.contains([tag]))    return session.exec(query).all()  async def POST(body: NewPost, session: Session = Depends(get_session)):    post = Post(title=body.title, tags=body.tags)    session.add(post)    session.commit()    session.refresh(post)    return JSONResponse(post.model_dump(mode="json"), status_code=201)

src/apps/posts/posts_api_controller.py

from pydantic import BaseModelfrom sqlmodel import Session, select from nexy.decorators import Controllerfrom nexy.http import Depends, JSONResponsefrom src.configs.session import get_sessionfrom src.models.post_model import Post  class NewPost(BaseModel):    title: str    tags: list[str] = []  @Controller("/api/posts")class PostsApiController:    async def get(self, tag: str | None = None, session: Session = Depends(get_session)):        query = select(Post).order_by(Post.published_at.desc())        if tag:            query = query.where(Post.tags.contains([tag]))        return session.exec(query).all()     async def post(self, body: NewPost, session: Session = Depends(get_session)):        post = Post(title=body.title, tags=body.tags)        session.add(post)        session.commit()        session.refresh(post)        return JSONResponse(post.model_dump(mode="json"), status_code=201)

List the controller in the controllers of the root module.

Post.tags.contains([tag]) is PostgreSQL's @>: the posts whose tags hold tag.

A `uuid` in the URL

src/routes/api/posts/[id].py

import uuid from sqlmodel import Session from nexy.http import Depends, HTTPExceptionfrom src.configs.session import get_sessionfrom src.models.post_model import Post  async def GET(id: uuid.UUID, session: Session = Depends(get_session)):    post = session.get(Post, id)    if post is None:        raise HTTPException(status_code=404, detail="No such post")    return post

src/apps/posts/posts_by_id_api_controller.py

import uuid from sqlmodel import Session from nexy.decorators import Controllerfrom nexy.http import Depends, HTTPExceptionfrom src.configs.session import get_sessionfrom src.models.post_model import Post  @Controller("/api/posts/{id}")class PostsByIdApiController:    async def get(self, id: uuid.UUID, session: Session = Depends(get_session)):        post = session.get(Post, id)        if post is None:            raise HTTPException(status_code=404, detail="No such post")        return post

List the controller in the controllers of the root module.

A segment that is not a UUID answers 404 before the query runs.

Query `JSONB`

src/services/posts.py

from sqlmodel import Session, select from src.configs.db import enginefrom src.models.post_model import Post  def featured_posts() -> list[Post]:    with Session(engine) as session:        query = select(Post).where(Post.extra["featured"].as_boolean())        return list(session.exec(query))

src/routes/featured.nexy

---from src.services.posts import featured_posts posts = featured_posts()---<ul>  {% for post in posts %}  <li>{{ post.title | e }}</li>  {% endfor %}</ul>

src/apps/featured/featured_view.nexy

---from src.services.posts import featured_posts posts = featured_posts()---<ul>  {% for post in posts %}  <li>{{ post.title | e }}</li>  {% endfor %}</ul>

src/apps/featured/featured_controller.py

from nexy.decorators import Controllerfrom nexy.hooks import useViews  @Controller("/featured")class FeaturedController:    async def get(self):        return useViews("src/apps/featured/featured_view.nexy")

Keep the query in a function: only the names assigned at the top level of the frontmatter reach the template.

Full-text search

src/routes/api/search.py

from sqlalchemy import funcfrom sqlmodel import Session, select from nexy.http import Dependsfrom src.configs.session import get_sessionfrom src.models.post_model import Post  async def GET(q: str, session: Session = Depends(get_session)):    document = func.to_tsvector("english", Post.title)    query = func.websearch_to_tsquery("english", q)    rank = func.ts_rank(document, query)    rows = session.exec(select(Post).where(document.op("@@")(query)).order_by(rank.desc()))    return rows.all()

src/apps/search/search_api_controller.py

from sqlalchemy import funcfrom sqlmodel import Session, select from nexy.decorators import Controllerfrom nexy.http import Dependsfrom src.configs.session import get_sessionfrom src.models.post_model import Post  @Controller("/api/search")class SearchApiController:    async def get(self, q: str, session: Session = Depends(get_session)):        document = func.to_tsvector("english", Post.title)        query = func.websearch_to_tsquery("english", q)        rank = func.ts_rank(document, query)        rows = session.exec(select(Post).where(document.op("@@")(query)).order_by(rank.desc()))        return rows.all()

List the controller in the controllers of the root module.

An index keeps it fast on a large table. Add it in a migration:

alembic/versions/xxxx_search_index.py

def upgrade() -> None:    op.execute(        "CREATE INDEX post_title_search ON post USING GIN (to_tsvector('english', title))"    )

Upserts

src/services/tags.py

from sqlalchemy.dialects.postgresql import insertfrom sqlmodel import Field, Session, SQLModel from src.configs.db import engine  class TagCount(SQLModel, table=True):    tag: str = Field(primary_key=True)    count: int = 0  def count_tag(tag: str) -> None:    statement = insert(TagCount).values(tag=tag, count=1)    statement = statement.on_conflict_do_update(        index_elements=[TagCount.tag], set_={"count": TagCount.count + 1}    )    with Session(engine) as session:        session.exec(statement)        session.commit()

Migrations

nx migrate --initnx migrate -m "create posts"nx migrate --upgrade

nx migrate reads DATABASE_URL, checks that the driver is installed and that the server answers, then runs Alembic. Import each model module in alembic/env.py so autogenerate sees it.

Async with `asyncpg`

src/configs/async_db.py

from sqlalchemy.ext.asyncio import create_async_enginefrom sqlmodel.ext.asyncio.session import AsyncSession from src.configs.db import database_url async_engine = create_async_engine(    database_url().replace("+psycopg", "+asyncpg", 1), pool_pre_ping=True)  async def get_async_session():    async with AsyncSession(async_engine) as session:        yield session

src/routes/api/posts/count.py

from sqlmodel import func, selectfrom sqlmodel.ext.asyncio.session import AsyncSession from nexy.http import Dependsfrom src.configs.async_db import get_async_sessionfrom src.models.post_model import Post  async def GET(session: AsyncSession = Depends(get_async_session)):    count = (await session.exec(select(func.count()).select_from(Post))).one()    return {"count": count}

src/apps/posts/posts_count_api_controller.py

from sqlmodel import func, selectfrom sqlmodel.ext.asyncio.session import AsyncSession from nexy.decorators import Controllerfrom nexy.http import Dependsfrom src.configs.async_db import get_async_sessionfrom src.models.post_model import Post  @Controller("/api/posts/count")class PostsCountApiController:    async def get(self, session: AsyncSession = Depends(get_async_session)):        count = (await session.exec(select(func.count()).select_from(Post))).one()        return {"count": count}

List the controller in the controllers of the root module, before PostsByIdApiController: the first controller whose path matches answers, and listed after it, /api/posts/count/ answers 404.

psycopg 3 also runs async: postgresql+psycopg:// works with create_async_engine as well.

Tests in a transaction

Each test runs inside a transaction that is rolled back, so the test database stays empty:

tests/conftest.py

import pytestfrom sqlmodel import Session, SQLModel, create_engine from nexy.app import appfrom src.configs.session import get_session test_engine = create_engine("postgresql+psycopg://postgres:secret@localhost:5432/app_test")SQLModel.metadata.create_all(test_engine)  @pytest.fixture(autouse=True)def session():    connection = test_engine.connect()    transaction = connection.begin()    session = Session(bind=connection, join_transaction_mode="create_savepoint")    app.dependency_overrides[get_session] = lambda: session    yield session    session.close()    transaction.rollback()    connection.close()

Managed PostgreSQL

Service	What changes
Neon	add `?sslmode=require`; use the pooled host for many short connections
Supabase	the same URL form; use the pooler port `6543` for many workers
Amazon RDS, Cloud SQL, Azure	add `?sslmode=require`, and allow the app's network

Next steps

Edit on GitHub

Use PostgreSQL with Nexy

Run PostgreSQL locally

Install the driver

The connection string

The engine

A model with PostgreSQL types

A session per request

Read and write from a handler

A uuid in the URL

Query JSONB

Full-text search

Upserts

Migrations

Async with asyncpg

Tests in a transaction

Managed PostgreSQL

Next steps

A `uuid` in the URL

Query `JSONB`

Async with `asyncpg`