data-finder 0.1.12

Model driven data finders

Data Finder

Data Finder is a model-driven query library for Python. You define your domain model and map it to a relational schema; the library generates type-safe Python Finder classes that let you query your data without writing SQL. Temporal versioning (milestoning) is a first-class concept, not an afterthought.

Overview

The workflow has three steps:

1. Define a model — describe your domain as classes and associations in Markdown.
2. Define a mapping — map each class property to a database table column in Markdown.
3. Generate finders — run the generator once to produce Python query classes.

Generated finders expose every mapped property as a typed method, and queries are assembled from those methods rather than from raw strings.

from finance.trade.trade_finder import TradeFinder

results = TradeFinder.find_all(
    processing_valid_at=datetime.datetime.now(),
    display_columns=[TradeFinder.symbol(), TradeFinder.price()],
    filter_op=TradeFinder.symbol().eq("AAPL"),
)
df = results.to_pandas()

---

Concepts

Class

A Class represents a logical entity — the equivalent of a UML class or a business object. It has a name, an optional description, and a set of properties.

### Class: Account

| Name    | Description                                     |
|---------|-------------------------------------------------|
| Account | Trading account used to buy and sell securities |

| Property | Id   | Type    | Key | Description |
|----------|------|---------|-----|-------------|
| Id       | id   | Integer | Y   |             |
| Name     | name | String  |     |             |

Each property has:

Column	Meaning
Property	Human-readable label used in generated docstrings
Id	Machine identifier used in code and mappings
Type	A primitive type or another class name (for navigations defined via Associations)
Key	Y marks the business key
Description	Optional documentation

Supported primitive types: String, Integer, Double, Float, Decimal, Date, DateTime, Boolean.

Classes belong to a Sub-Domain (package), which controls the Python package structure of the generated finders.

## Sub-Domain: finance.reference_data

### Class: Account
...

A sub-domain with a dotted name (finance.reference_data) generates a nested package hierarchy.

Inheritance

A class can extend one or more parent classes:

### Class: Employee extends Person, Contactable

All inherited properties are available via all_properties() and appear in the generated finder.

Association

An Association declares a named relationship between two classes. Both ends carry an explicit property name — the name that will appear as a navigation method in the generated finder.

### Association: TradeAccount

| Name         | Source | Source Property Name | Source Property ID | Source Multiplicity | Target  | Target Property Name | Target Property ID | Target Multiplicity | Description                  |
|--------------|--------|----------------------|--------------------|---------------------|---------|----------------------|--------------------|---------------------|------------------------------|
| TradeAccount | Trade  | Trades               | trades             | *                   | Account | Account              | account            | 1                   | Links a trade to its account |

Column	Meaning
Source	Name of the source class
Source Property Name	Display name of the reverse navigation property added to the target class (Account.trades)
Source Property ID	camelCase id of the reverse navigation property (trades)
Source Multiplicity	* (many) or 1 (one) — multiplicity on the source side
Target	Name of the target class
Target Property Name	Display name of the forward navigation property added to the source class (Trade.account)
Target Property ID	camelCase id of the forward navigation property (account)
Target Multiplicity	* (many) or 1 (one) — multiplicity on the target side

All eight fields (name and id for both properties, both multiplicities) are mandatory. The association is the single source of truth for cross-class navigation — do not also declare the same property explicitly on the class.

When an association is loaded, both navigation properties are automatically available via all_properties() on the relevant classes and generate methods in the finder.

---

Mapping

A Mapping file connects the logical model to the physical relational schema. It references one or more model files, declares the data store, and maps each class to a table.

Structure

# Finance Mapping

## Model: finance.md
## Model: finance_trade.md

## DataStore: finance_db (Database)

| Scheme                   | processing_start | processing_end | business_date |
|--------------------------|------------------|----------------|---------------|
| processing_only          | in_z             | out_z          |               |
| business_date_processing | in_z             | out_z          | DATE          |

### Schema: ref_data

#### Table: account_master → Account

| Column    | Type    | Key | Property ID |
|-----------|---------|-----|-------------|
| ID        | INT     | PK  | id          |
| ACCT_NAME | VARCHAR |     | name        |

### Schema: trading

#### Table: trades → Trade (milestoning: processing_only)

| Column     | Type      | Key | Property ID |
|------------|-----------|-----|-------------|
| sym        | VARCHAR   |     | symbol      |
| price      | DOUBLE    |     | price       |
| account_id | INT       | FK  | account     |
| in_z       | TIMESTAMP |     | validFrom   |
| out_z      | TIMESTAMP |     | validTo     |

#### Association: TradeAccount

| Source Column | Target Table   | Target Column |
|---------------|----------------|---------------|
| account_id    | account_master | ID            |

Table mapping

#### Table: <table_name> → <ClassName> maps a database table to a class. The Property ID column references the property Id defined in the model.

For foreign-key columns that represent association navigations, set Key to FK and use the association's Target Property ID as the property name. Follow the table block immediately with an #### Association: block that provides the join target.

Association mapping

#### Association: <AssociationName> specifies how the foreign key joins to the target table.

Column	Meaning
Source Column	The FK column in the source table
Target Table	The table the FK references
Target Column	The primary key column in the target table

Milestoning

Milestoning lets you query data as it was at a specific point in time. Declare named milestoning schemes on the DataStore and reference them per table.

Scheme	Required columns	find_all signature
processing_only	processing_start, processing_end	processing_valid_at
business_date	business_date	business_date, processing_valid_at
business_date_processing	processing_start, processing_end, business_date	business_date, processing_valid_at
bitemporal	processing_start, processing_end, business_date_from, business_date_to	business_date, processing_valid_at

Tag a table with the scheme name in parentheses:

#### Table: trades → Trade (milestoning: processing_only)

---

Generating Finders

Load the mapping markdown and call generate:

from mapping_markdown.markdown_mapping import load
from datafinder_generator.generator import generate

mapping = load("finance_mapping.md")
generate(mapping, output_directory="src/")

This writes one <classname>_finder.py file per mapped class, organised into the package structure declared by the sub-domain names.

Refreshing a mapping from a live database

If you have a DuckDB database you can auto-populate the mapping skeleton from the live schema:

uv run example/refresh_mapping.py path/to/finance.db finance_mapping.md

---

Using the Generated Finders

Simple queries

from finance.reference_data.account_finder import AccountFinder

# All accounts
result = AccountFinder.find_all(
    display_columns=[AccountFinder.id(), AccountFinder.name()],
)

# Filtered
result = AccountFinder.find_all(
    display_columns=[AccountFinder.id(), AccountFinder.name()],
    filter_op=AccountFinder.name().eq("Acme Corp"),
)
df = result.to_pandas()

Temporal queries

For milestoned tables, supply the temporal arguments:

import datetime
from finance.trade.trade_finder import TradeFinder

# Trades as of now (processing_only milestoning)
result = TradeFinder.find_all(
    processing_valid_at=datetime.datetime.now(),
    display_columns=[TradeFinder.symbol(), TradeFinder.price()],
    filter_op=TradeFinder.symbol().eq("AAPL"),
)

# Positions on a specific business date as processed at a specific time
from finance.trade.contractualposition_finder import ContractualPositionFinder

result = ContractualPositionFinder.find_all(
    business_date=datetime.date(2023, 1, 15),
    processing_valid_at=datetime.datetime(2023, 1, 16),
    display_columns=[ContractualPositionFinder.quantity(), ContractualPositionFinder.npv()],
)

Navigating associations

Forward navigation — from Trade to its Account:

result = TradeFinder.find_all(
    processing_valid_at=datetime.datetime.now(),
    display_columns=[
        TradeFinder.symbol(),
        TradeFinder.account().name(),   # navigates the TradeAccount association
    ],
)

Reverse navigation — from Account to all its Trades (generated from Source Property ID: trades):

result = AccountFinder.find_all(
    display_columns=[
        AccountFinder.name(),
        AccountFinder.trades().symbol(),
        AccountFinder.trades().price(),
    ],
)

Result formats

result.to_pandas()   # pandas DataFrame
result.to_numpy()    # NumPy array

---

Project Layout

Directory	Contents
model/	Core metamodel (Class, Property, Association, Package)
model_markdown/	Load and save model definitions from Markdown
mapping_markdown/	Load and save mapping definitions from Markdown
datafinder/	Query engine — FinderResult, filter operations, typed attributes
datafinder_generator/	Jinja2-based code generator that produces Finder classes
datafinder_ibis/	Ibis backend for query execution
datafinder_ibis_duckdb/	DuckDB integration via Ibis
datafinder_duckdb/	Schema reader — introspects a live DuckDB database
example/	End-to-end example with finance model, mapping, and queries

---

Development

This project uses uv. To run the tests:

uv run pytest

To add a dependency to a sub-project:

uv add --optional <group> <package>