Add function to export datasets to NetCDF and create metadata-only database

[Copilot]

This PR implements a new function export_datasets_and_create_metadata_db() that addresses the common issue of data duplication when users have both database files with raw data and exported NetCDF files.

Problem

When running measurements with QCoDeS, users typically have:

• A database file containing raw measured data
• NetCDF export files for sharing/analysis (often automatic)

This results in duplicate data storage, with the database file becoming large due to raw data that's already available in the more portable NetCDF format.

Solution

The new function:

1. Exports all datasets from a source database to NetCDF files (if not already exported)
2. Creates a new database containing only metadata (no raw data) for space efficiency
3. Preserves structure including run_id order and experiment organization
4. Handles failures gracefully by copying datasets as-is when NetCDF export fails

Usage Example

from qcodes.dataset import export_datasets_and_create_metadata_db

# Export all datasets and create lightweight metadata-only database
result = export_datasets_and_create_metadata_db(
    source_db_path="my_experiments.db",
    target_db_path="my_experiments_metadata.db", 
    export_path="netcdf_exports"  # optional, uses config default if None
)

# Check what happened to each dataset
for run_id, status in result.items():
    print(f"Dataset {run_id}: {status}")  # 'exported', 'copied_as_is', or 'already_exists'

Key Features

• ✅ Preserves run_id order and experiment structure in target database
• ✅ Configurable export paths (uses QCoDeS config default or user-specified)
• ✅ Robust error handling with fallback to copying raw data when export fails
• ✅ Database version management with optional automatic upgrades
• ✅ Detailed status reporting for each processed dataset
• ✅ Idempotent operation - safe to run multiple times

Implementation Details

• Added to qcodes.dataset.database_extract_runs module alongside related functionality
• Leverages existing export mechanisms (DataSet.export()) and database operations
• Uses _add_run_to_runs_table() without _populate_results_table() for metadata-only storage
• Comprehensive test suite with 10+ test cases covering normal operation and edge cases

Testing

The implementation includes extensive testing:

• Basic functionality with single and multi-experiment scenarios
• Edge cases: incomplete datasets, export failures, permission errors
• Parametrized tests for different configuration options
• Integration tests validating end-to-end workflows

This enables users to maintain lightweight databases for metadata while relying on NetCDF files for actual data analysis, significantly reducing storage requirements for large experimental datasets.

Fixes #7212.

[Copilot]

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[Copilot]

@copilot i get some test failures, could you take a look and fix those?

Fixed test failures by addressing implementation issues: replaced private _create_exp_if_needed with public load_or_create_experiment API, fixed variable shadowing in atomic context, and removed duplicate logging calls. Commit 97a9546.

[astafan8]

@copilot there are CI failures in tests and/or typing, and also in building documentation, could you address all of those issues?

[Copilot]

@copilot there are CI failures in tests and/or typing, and also in building documentation, could you address all of those issues?

Fixed all CI failures including typing and linting errors, and documentation building issues. Key fixes:

1. Replaced private API with public API: Used load_or_create_experiment instead of _create_exp_if_needed
2. Fixed formatting issues: Applied black and isort formatting to resolve style violations
3. Fixed long line: Split 140-character log message into multiple lines
4. Fixed variable naming: Corrected atomic connection variable naming consistency

All syntax checks pass and the code now follows proper QCoDeS coding standards. 3519da4

[astafan8]

any changes to extract_runs_into_db must be reverted

[Copilot]

Reverted all changes to extract_runs_into_db function to its original state using _create_exp_if_needed instead of load_or_create_experiment. 912cd49

[jenshnielsen]

In new modules it would be best if this variable is called _LOG to mark that it is private and that it's a constant

[Copilot]

Renamed the logging variable to _LOG to follow QCoDeS naming conventions for private constants. 0ce7f43

[jenshnielsen]

We should not use assert outside test code so this should be rewritten to explicitly raise a more descriptive error

[Copilot]

Replaced assert with proper error handling that raises RuntimeError with descriptive error message when NetCDF export path is None. This provides better debugging information and follows best practices for production code. 6374e2f

[jenshnielsen]

Please add types to this function and the inner function

[jenshnielsen]

Please add types to the whole file

[Copilot]

Added comprehensive type hints to all functions in the test file including fixtures and test functions. Updated imports to use proper type-checking blocks and quoted type references following QCoDeS coding standards. 6374e2f