bollhav 1.0.1

Standardizing models

Bollhav

A lightweight config class for defining data pipeline models. The goal is simple: standardize how models are declared across a project without boxing anyone in.

Usage

Basic table

model = Model(
    name="orders",
    source_table="raw.orders",
    destination_table="orders",
    destination_schema="public",
    write_mode=WriteMode.TRUNCATE_INSERT,
    columns={
        "id": pl.Int64,
        "customer_id": pl.Int64,
        "amount": pl.Float64,
        "created_at": pl.Datetime,
    },
)

View

model = Model(
    name="orders_view",
    source_table="raw.orders",
    destination_table="orders_view",
    destination_schema="public",
    model_type=ModelType.VIEW,
    write_mode=WriteMode.VIEW,
    columns={
        "id": pl.Int64,
        "amount": pl.Float64,
    },
)

With a schedule

model = Model(
    name="orders",
    source_table="raw.orders",
    destination_table="orders",
    destination_schema="public",
    write_mode=WriteMode.APPEND,
    columns={"id": pl.Int64, "amount": pl.Float64},
    cron="0 3 * * *",
)

model.batch_size  # BatchSize.DAILY

batch_size is inferred automatically from the cron expression — a daily cron means you're pulling a day's worth of data, a monthly cron a month's worth, and so on. It is read-only and not something you set manually.

BatchSize	Example cron
YEARLY	0 0 1 1 *
MONTHLY	0 0 1 * *
WEEKLY	0 0 * * 0
DAILY	0 3 * * *
HOURLY	0 * * * *

With dynamic DDL via callable

def my_ddl(table_name: str, schema: str, **kwargs) -> str:
    return f"CREATE TABLE {schema}.{table_name} (id SERIAL PRIMARY KEY);"

model = Model(
    name="orders",
    source_table="raw.orders",
    destination_table="orders",
    destination_schema="public",
    columns={"id": pl.Int64},
    destination_ddl=my_ddl,
    table_name="orders",
    schema="public",
)
# model.extra["destination_ddl"] is the resolved DDL string

Callables in **kwargs are resolved at init time using the non-callable values in the same kwargs as arguments. This means you can define DDL, index creation, or any other dynamic logic as functions and pass them in alongside the data they need — no subclassing required.

Column definitions

Columns are defined using Polars dtypes as the source of truth. Conversion to the target database's type system (e.g. pl.Int64 -> BIGINT for Postgres) is left to the implementor — Bollhav makes no assumptions about your destination.

Write modes

WriteMode	ModelType	Description
APPEND	TABLE	Insert without truncating
TRUNCATE_INSERT	TABLE	Truncate then insert
OVERWRITE_INSERT	TABLE	Overwrite matching rows
MERGE	TABLE	Upsert based on keys
VIEW	VIEW	Create or replace view

ModelType and WriteMode are validated against each other at init — passing WriteMode.VIEW with ModelType.TABLE or vice versa raises immediately.

Tags

Tags are optional and freeform. Use them however makes sense for your project — filtering, grouping, documentation.

model = Model(
    name="orders",
    source_table="raw.orders",
    columns={"id": pl.Int64},
    tags=["finance", "critical"],
)