Add metadata for DatabaseReader

[cluic]

Description

Add Metadata Functionality to DatabaseReader
In the original implementation, the DatabaseReader loaded all the data into text format. However, sometimes we don't need to retrieve all the columns; we only need some fields as metadata. Therefore, I have updated the load_data method.

With this update, we can now load data from the database and specify certain fields to be included as metadata. Here a simple example:

from llama_index.readers.database import DatabaseReader

reader = DatabaseReader(uri="sqlite:///D:/AAA/BBB/msg.db?table=msg")

# load data from database
documents = reader.load_data(
    query="SELECT msgid, content, sender, timestamp FROM msg", 
    doc_cols=["content"],
    metadata_cols=["msgid", "sender", "timestamp"], 
)

Fixes # (issue)

New Package?

Did I fill in the tool.llamahub section in the pyproject.toml and provide a detailed README.md for my new integration or package?

• Yes
• No

Version Bump?

Did I bump the version in the pyproject.toml file of the package I am updating? (Except for the llama-index-core package)

• Yes
• No

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Added new unit/integration tests
• Added new notebook (that tests end-to-end)
• I stared at the code and made sure it makes sense

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added Google Colab support for the newly added notebooks.
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I ran make format; make lint to appease the lint gods

[cluic]

Hi maintainers,

I have updated the DatabaseReader to include metadata functionality. Could you please review my PR and approve the workflows?

Thank you!

[nerdai]

Thanks @cluic for the contribution. I've left some comments.

[nerdai]

from typing import Dict, List

def load_data(
    self,
    query: str,
    metadata: Dict = {},
    doc_cols: List = [],
    metadata_cols: List = []
)

Rather than Optional, I think you can just set defaults as I did above.

[nerdai]

Please also use the types that I've indicated above, otherwise mypy might complain

[nerdai]

Please also run make lint and make format then commit and push changes.