sqla-autoloads 0.1.0

Automatic relationship eager-loading for SQLAlchemy — LATERAL, dotted paths, self-refs, conditions

sqla-autoloads

Automatic relationship eager-loading for SQLAlchemy. Build SELECT queries with LATERAL subqueries, dotted-path traversal, self-referential handling, and per-relationship conditions — all from a single function call.

Install

pip install sqla-autoloads

Quick Start

from sqla_autoloads import init_node, get_node, sqla_select

# 1. Initialize once at startup
init_node(get_node(Base))

# 2. Query with eager-loading
query = sqla_select(model=User, loads=("posts", "roles"))
result = await session.execute(query)
users = result.unique().scalars().all()
# users[0].posts  — already loaded, no N+1

Why?

Loading relationships in SQLAlchemy requires writing boilerplate joins and loader options for every combination of relationships. This grows quickly — especially with optional loads, LATERAL limits, and deep chains.

Raw SQLAlchemy — manual if per relationship:

UserLoad = Literal["posts", "roles", "profile"]

async def get_users(*loads: UserLoad) -> list[User]:
    query = sa.select(User)
    options = []
    if "posts" in loads:
        lateral = (
            sa.select(Post)
            .where(Post.author_id == User.id)
            .order_by(Post.id.desc())
            .limit(50)
            .lateral()
        )
        query = query.outerjoin(lateral, sa.true())
        options.append(orm.contains_eager(User.posts, alias=lateral))
    if "roles" in loads:
        query = query.outerjoin(user_roles).outerjoin(Role)
        options.append(orm.contains_eager(User.roles))
    if "profile" in loads:
        query = query.outerjoin(Profile)
        options.append(orm.contains_eager(User.profile))
    if options:
        query = query.options(*options)
    return (await session.execute(query)).unique().scalars().all()

sqla-autoloads — one call, on-demand:

UserLoad = Literal["posts", "roles", "profile"]

async def get_users(*loads: UserLoad) -> list[User]:
    query = sqla_select(model=User, loads=loads)
    return (await session.execute(query)).unique().scalars().all()

Features

• LATERAL subqueries with configurable limit (default 50 per relationship)
• Dotted paths — "posts.comments.reactions" traverses the chain automatically
• Self-referential relationships — parent/children on the same model
• M2M through association tables
• Multiple FKs to the same table (e.g. from_user, to_user, owner)
• Per-relationship conditions via add_conditions
• Automatic strategy selection — contains_eager, selectinload, joinedload, subqueryload
• LRU-cached query construction — same parameters return the same compiled query
• Async-first, sync-compatible
• Fully typed (PEP 561 py.typed marker)

Usage

Basic loads

# One-to-many
query = sqla_select(model=User, loads=("posts",))

# Many-to-many
query = sqla_select(model=User, loads=("roles",))

# Many-to-one / one-to-one
query = sqla_select(model=Post, loads=("author",))

# Multiple relationships at once
query = sqla_select(model=User, loads=("posts", "roles", "profile"))

Deep / dotted paths

# Load posts → comments → reactions in one query
query = sqla_select(model=User, loads=("posts.comments.reactions",))

Conditions

from sqla_autoloads import add_conditions

query = sqla_select(
    model=User,
    loads=("posts", "roles"),
    conditions={
        "roles": add_conditions(Role.level > 3),
    },
)

Limit and ordering

# Custom limit per relationship (default is 50)
query = sqla_select(model=User, loads=("posts",), limit=10)

# No limit — load all related rows (uses subqueryload/selectinload)
query = sqla_select(model=User, loads=("posts",), limit=None)

# Custom ordering
query = sqla_select(model=User, loads=("posts",), order_by=("title",))

Self-referential

query = sqla_select(
    model=Category,
    loads=("children", "parent"),
    self_key="parent_id",
)

Extending an existing query

base = sa.select(User).where(User.active == True)
query = sqla_select(model=User, loads=("posts",), query=base)

Many-load strategy

# Use selectinload instead of default subqueryload for limit=None
query = sqla_select(model=User, loads=("posts",), limit=None, many_load="selectinload")

Important notes

LATERAL support — database compatibility

The limit parameter (default 50) uses LATERAL subqueries to cap the number of related rows per parent. LATERAL is supported by PostgreSQL and MySQL 8.0+ only.

SQLite, MariaDB, and MSSQL do not support LATERAL. On these databases, pass limit=None to disable LATERAL and fall back to subqueryload/selectinload:

query = sqla_select(model=User, loads=("posts",), limit=None)

.unique() is required on results

sqla_select uses outerjoin + contains_eager and joinedload to load relationships. These strategies produce duplicate parent rows in the raw result (one row per related object). This is standard SQLAlchemy behavior.

You must call .unique() on the result before .scalars():

result = await session.execute(query)
users = result.unique().scalars().all()

Without .unique(), SQLAlchemy will raise an error or return duplicate objects.

Note: The distinct=True parameter in sqla_select applies SQL-level DISTINCT, which deduplicates by column values. It does not replace .unique(), which deduplicates by object identity.

API Reference

Function	Description
sqla_select(**params)	Build a SELECT with eager-loaded relationships
init_node(mapping)	Initialize the relationship graph singleton (call once at startup)
get_node(Base)	Extract relationship mapping from a declarative base
add_conditions(*exprs)	Create a condition function for filtering loaded relationships
Node()	Access the singleton relationship graph
SelectBuilder	Query builder class (used internally, also exported)

sqla_select parameters

Parameter	Type	Default	Description
model	type[T]	required	SQLAlchemy model class
loads	tuple[str, ...]	()	Relationship paths to eager-load
limit	int | None	50	LATERAL limit per relationship (None = no limit)
conditions	Mapping[str, Callable]	None	Per-relationship WHERE conditions
order_by	tuple[str, ...]	None	Column names for ordering (default: PK desc)
query	sa.Select	None	Existing query to extend
self_key	str	auto-detected	FK column for self-referential relationships
many_load	str	"subqueryload"	Strategy for limit=None: "subqueryload" or "selectinload"
distinct	bool	False	Apply DISTINCT to the query
check_tables	bool	False	Check for existing tables to avoid duplicate joins

Requirements

• Python 3.10+
• SQLAlchemy 2.0+

License

MIT