File attachment feature

[seancolsen]

This is a tracking branch for the File Attachments feature. All changes in this branch have already been reviewed in other PRs.

This PR will be ready to merge once we've decided that the Files feature is ready for release.

Testing Instructions

Setup

1. Checkout this branch git checkout file_attachment_feature or gh pr checkout 4757
2. Configure the default file backend by copying the example config cp file_storage.yml.example file_storage.yml
3. Run Mathesar's dev service and the new local file storage container (MinIO) with:

   docker compose -f docker-compose.dev.yml up obj-store dev-service --build
   #                                           ^^^^^^^^^ THIS IS NEW

4. Log into MinIO at localhost:9001. Username and password are both "mathesar".
5. Create a new bucket called "mathesar-storages" in the UI.
6. Go to Mathesar.

Testing

1. Go to an existing table in your local Mathesar instance, or create a new schema with one of the pre-defined datasets and navigate to a table.
2. Using the "+" icon, add a new "File" column to the table.
3. Upload various files to cells. Images and non-images.
4. Experiment with various aspects of the UI:

• The single record view of a record with a file column
• Attempting to add a file column to as form
• The lightbox when clicking on an image thumbnail
• The modal when clicking on an non-image file icon

Video

A very quick showcase of the core functionality:

Screencast.From.2025-09-22.11-19-21.mp4

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the develop branch of the repository
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

Developer Certificate of Origin

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[kgodey]

Very nice work @mathemancer @seancolsen @pavish @Anish9901 @zackkrida! Looks great!

I'm approving but I have two issues that would be good to fix before release (they don't have to block merge).

Issue 1

The buttons on this modal are too far apart. I recommend consolidating them in the center.

Issue 2

This copy is not relevant to most end users and increases cognitive load. It is primarily only relevant to Mathesar admins. We should have this caveat be prominently displayed in our docs, but we do not need to have this be a message here.

It's okay if we have a confirmation dialog, I just don't want the copy about the file reference.

[zackkrida]

Awesome, thanks @kgodey! I'll create standalone issues for the UI changes you've identified, and we'll fix them this week as part of QA.