Contract Builder - PyCharter
Description: Data Contract Management, ETL Pipelines, and Quality Assurance for Python

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# Contract Builder

Build consolidated contracts from separate artifacts.

## Overview

    from pycharter import build_contract, ContractArtifacts

    artifacts = ContractArtifacts(
        schema=schema,
        coercion_rules=coercion,
        validation_rules=validation
    )
    contract = build_contract(artifacts)

## Contract Structure

Schema is RAW

The contract dict contains raw schema + separate rules. Rules are NOT merged into the schema. The `Validator` class handles merging internally during validation.

The returned contract always has this structure:

    {
        "schema": {...},           # RAW schema (no coercion/validation merged)
        "coercion_rules": {...},   # Separate coercion rules (always present, may be {})
        "validation_rules": {...}, # Separate validation rules (always present, may be {})
        "metadata": {...},         # Optional metadata
        "ownership": {...},        # Optional ownership
        "governance_rules": {...}, # Optional governance
        "ontology": {...},         # Optional ontology (semantic field annotations)
        "versions": {...}          # Version tracking
    }

To get a merged schema (for display or legacy code), use:

    from pycharter import get_merged_schema_from_contract

    merged_schema = get_merged_schema_from_contract(contract)
    # merged_schema["properties"]["age"]["coercion"] now exists

## API Reference

## `` build_contract

    build_contract(
        artifacts: ContractArtifacts,
        include_metadata: bool = True,
        include_ownership: bool = True,
        include_governance: bool = True,
    ) -> dict[str, Any]

Build a consolidated data contract from separate artifacts.

This function combines schema, coercion rules, validation rules, and metadata into a single consolidated contract. It tracks versions of all components.

IMPORTANT: The schema in the returned contract is RAW (not merged with rules). The Validator class handles merging rules into the schema internally during validation. To get a merged schema explicitly, use merge_rules_into_schema() from pycharter.runtime_validator.utils.

Parameters:

Name | Type | Description | Default
--- | --- | --- | ---
`artifacts` | `ContractArtifacts` | ContractArtifacts object containing all separate artifacts | required
`include_metadata` | `bool` | Whether to include metadata in the contract | `True`
`include_ownership` | `bool` | Whether to include ownership information | `True`
`include_governance` | `bool` | Whether to include governance rules | `True`

Returns:

Name | Type | Description
--- | --- | ---
| `dict[str, Any]` | Consolidated contract dictionary with:
| `dict[str, Any]` | schema: RAW schema (no coercion/validation merged; must have version)
| `dict[str, Any]` | coercion_rules: Coercion rules dictionary (always present, may be empty)
| `dict[str, Any]` | validation_rules: Validation rules dictionary (always present, may be empty)
| `dict[str, Any]` | metadata: Metadata containing ownership and governance_rules (if include_metadata=True)
| `dict[str, Any]` | ontology: Ontology annotations (if present in artifacts)
| `dict[str, Any]` | versions: Dictionary tracking versions of all components
`Note` | `dict[str, Any]` | ownership and governance_rules are nested inside metadata, not at top level.

Raises:

Type | Description
--- | ---
`ValueError` | If schema does not have a version field

Example

> > > artifacts = ContractArtifacts( ... schema={"type": "object", "version": "1.0.0", "properties": {"age": {"type": "integer"}}}, ... coercion_rules={"version": "1.0.0", "rules": {"age": "coerce_to_integer"}}, ... validation_rules={"version": "1.0.0", "rules": {}}, ... metadata={"version": "1.0.0", "description": "User contract"}, ... ownership={"owner": "data-team"}, ... governance_rules={} ... ) contract = build_contract(artifacts) list(contract["versions"].keys()) ['schema', 'coercion_rules', 'validation_rules', 'metadata'] "coercion" not in (contract["schema"].get("properties") or {}).get("age", {}) True

Source code in `src/pycharter/contract_builder/builder.py`

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    def build_contract(
        artifacts: ContractArtifacts,
        include_metadata: bool = True,
        include_ownership: bool = True,
        include_governance: bool = True,
    ) -> dict[str, Any]:
        """
        Build a consolidated data contract from separate artifacts.

        This function combines schema, coercion rules, validation rules, and metadata
        into a single consolidated contract. It tracks versions of all components.

        IMPORTANT: The schema in the returned contract is RAW (not merged with rules).
        The Validator class handles merging rules into the schema internally during
        validation. To get a merged schema explicitly, use merge_rules_into_schema()
        from pycharter.runtime_validator.utils.

        Args:
            artifacts: ContractArtifacts object containing all separate artifacts
            include_metadata: Whether to include metadata in the contract
            include_ownership: Whether to include ownership information
            include_governance: Whether to include governance rules

        Returns:
            Consolidated contract dictionary with:
            - schema: RAW schema (no coercion/validation merged; must have version)
            - coercion_rules: Coercion rules dictionary (always present, may be empty)
            - validation_rules: Validation rules dictionary (always present, may be empty)
            - metadata: Metadata containing ownership and governance_rules (if include_metadata=True)
            - ontology: Ontology annotations (if present in artifacts)
            - versions: Dictionary tracking versions of all components

            Note: ownership and governance_rules are nested inside metadata, not at top level.

        Raises:
            ValueError: If schema does not have a version field

        Example:
            >>> artifacts = ContractArtifacts(
            ...     schema={"type": "object", "version": "1.0.0", "properties": {"age": {"type": "integer"}}},
            ...     coercion_rules={"version": "1.0.0", "rules": {"age": "coerce_to_integer"}},
            ...     validation_rules={"version": "1.0.0", "rules": {}},
            ...     metadata={"version": "1.0.0", "description": "User contract"},
            ...     ownership={"owner": "data-team"},
            ...     governance_rules={}
            ... )
            >>> contract = build_contract(artifacts)
            >>> list(contract["versions"].keys())
            ['schema', 'coercion_rules', 'validation_rules', 'metadata']
            >>> "coercion" not in (contract["schema"].get("properties") or {}).get("age", {})
            True
        """
        if not artifacts.schema:
            raise ValueError("Schema is required to build a contract")

        # Validate schema has version
        if "version" not in artifacts.schema:
            raise ValueError(
                "Schema must have a 'version' field. All schemas must be versioned. "
                "Please ensure the schema dictionary contains 'version': '<version_string>'."
            )

        # Deep copy schema to avoid modifying original - NO MERGING
        # The Validator class handles merging internally during validation
        raw_schema = copy.deepcopy(artifacts.schema)

        # Extract rules (but do NOT merge into schema)
        coercion_rules = _extract_rules(artifacts.coercion_rules) or {}
        validation_rules = _extract_rules(artifacts.validation_rules) or {}

        # Build contract with raw schema and separate rules
        contract: dict[str, Any] = {
            "schema": raw_schema,
            "coercion_rules": copy.deepcopy(coercion_rules) if coercion_rules else {},
            "validation_rules": copy.deepcopy(validation_rules) if validation_rules else {},
        }

        # Track versions
        versions: dict[str, str | None] = {}

        # Extract version from schema
        schema_version = _extract_version(artifacts.schema)
        if schema_version:
            versions["schema"] = schema_version

        # Extract version from coercion rules
        if artifacts.coercion_rules:
            coercion_version = _extract_version(artifacts.coercion_rules)
            if coercion_version:
                versions["coercion_rules"] = coercion_version

        # Extract version from validation rules
        if artifacts.validation_rules:
            validation_version = _extract_version(artifacts.validation_rules)
            if validation_version:
                versions["validation_rules"] = validation_version

        # Extract version from metadata
        if artifacts.metadata:
            metadata_version = _extract_version(artifacts.metadata)
            if metadata_version:
                versions["metadata"] = metadata_version

        # Extract version from ontology
        if artifacts.ontology:
            ontology_version = _extract_version(artifacts.ontology)
            if ontology_version:
                versions["ontology"] = ontology_version

        # Add metadata if requested
        if include_metadata and artifacts.metadata:
            # Create metadata dict without version (version is tracked separately)
            metadata_dict = copy.deepcopy(artifacts.metadata)
            metadata_dict.pop("version", None)  # Remove version, it's in versions dict

            # Add ownership inside metadata if requested
            if include_ownership and artifacts.ownership:
                metadata_dict["ownership"] = copy.deepcopy(artifacts.ownership)

            # Add governance rules inside metadata if requested
            if include_governance and artifacts.governance_rules:
                metadata_dict["governance_rules"] = copy.deepcopy(
                    artifacts.governance_rules
                )

            contract["metadata"] = metadata_dict

        # Also expose ownership and governance_rules at top level for easier access
        if include_ownership and artifacts.ownership:
            contract["ownership"] = copy.deepcopy(artifacts.ownership)

        if include_governance and artifacts.governance_rules:
            contract["governance_rules"] = copy.deepcopy(artifacts.governance_rules)

        # Add ontology if present
        if artifacts.ontology:
            contract["ontology"] = copy.deepcopy(artifacts.ontology)

        # Add versions tracking
        if versions:
            contract["versions"] = versions

        return contract

## `` build_contract_from_store

    build_contract_from_store(
        store: MetadataStoreClient,
        contract_name: str,
        contract_version: str,
        include_metadata: bool = True,
        include_ownership: bool = True,
        include_governance: bool = True,
    ) -> dict[str, Any]

Build a consolidated data contract from the metadata store by contract name and version.

Uses store.get_contract(contract_name, contract_version, ...) to load the full contract (schema + coercion_rules + validation_rules + metadata + ontology).

Parameters:

Name | Type | Description | Default
--- | --- | --- | ---
`store` | `MetadataStoreClient` | MetadataStoreClient instance (contract-centric) | required
`contract_name` | `str` | Data contract name | required
`contract_version` | `str` | Data contract version | required
`include_metadata` | `bool` | Whether to include metadata in the contract | `True`
`include_ownership` | `bool` | Whether to include ownership information | `True`
`include_governance` | `bool` | Whether to include governance rules | `True`

Returns:

Type | Description
--- | ---
`dict[str, Any]` | Consolidated contract dictionary ready for runtime validation

Raises:

Type | Description
--- | ---
`ValueError` | If the contract (or its schema) is not found

Source code in `src/pycharter/contract_builder/builder.py`

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    def build_contract_from_store(
        store: MetadataStoreClient,
        contract_name: str,
        contract_version: str,
        include_metadata: bool = True,
        include_ownership: bool = True,
        include_governance: bool = True,
    ) -> dict[str, Any]:
        """
        Build a consolidated data contract from the metadata store by contract name and version.

        Uses store.get_contract(contract_name, contract_version, ...) to load the full
        contract (schema + coercion_rules + validation_rules + metadata + ontology).

        Args:
            store: MetadataStoreClient instance (contract-centric)
            contract_name: Data contract name
            contract_version: Data contract version
            include_metadata: Whether to include metadata in the contract
            include_ownership: Whether to include ownership information
            include_governance: Whether to include governance rules

        Returns:
            Consolidated contract dictionary ready for runtime validation

        Raises:
            ValueError: If the contract (or its schema) is not found
        """
        contract = store.get_contract(
            contract_name,
            contract_version,
            include_metadata=include_metadata,
            include_ownership=include_ownership,
            include_governance=include_governance,
        )
        if contract is None:
            raise ValueError(
                f"Contract not found: {contract_name!r} @ {contract_version!r}. "
                "Ensure the schema is stored for this contract."
            )
        if not contract.get("schema"):
            raise ValueError(
                f"Contract {contract_name!r} @ {contract_version!r} has no schema."
            )
        if "version" not in contract["schema"]:
            raise ValueError(
                f"Contract {contract_name!r} @ {contract_version!r} schema does not have a version field."
            )
        return contract

## ContractArtifacts

Input for building contracts:

Attribute | Type | Description
--- | --- | ---
`schema` | Dict | JSON Schema (will be stored as-is, not modified)
`coercion_rules` | Dict | Coercion rules (stored separately)
`validation_rules` | Dict | Validation rules (stored separately)
`metadata` | Dict | Metadata
`ownership` | Dict | Ownership
`governance_rules` | Dict | Governance
`ontology` | Dict | Ontology (version, fields with concept/definition/relationships)

## Examples

    from pycharter import build_contract, build_contract_from_store, ContractArtifacts, Validator

    # Build from artifacts
    artifacts = ContractArtifacts(
        schema={"type": "object", "version": "1.0.0", "properties": {"age": {"type": "integer"}}},
        coercion_rules={"rules": {"age": "coerce_to_integer"}},
        validation_rules={"rules": {"age": {"is_positive": {"threshold": 0}}}}
    )
    contract = build_contract(artifacts)

    # Schema is RAW - rules are separate
    print(contract["schema"]["properties"]["age"])  # {"type": "integer"} - no coercion
    print(contract["coercion_rules"])  # {"age": "coerce_to_integer"}

    # Use Validator for validation (it merges internally)
    validator = Validator(contract_dict=contract)
    result = validator.validate({"age": "25"})  # Coercion applied automatically

    # Build from store
    contract = build_contract_from_store(store, "user_schema")

## See Also

- Contract Parser
- Metadata Store
- Validator