# Working with Unity Catalog Volumes

`{brickster}` includes two groups of volume functions:

- `db_uc_volumes_*`: manage volume objects in Unity Catalog (create, list, update, delete)
- `db_volume_*`: work with files and directories inside an existing volume

In most day-to-day workflows, you will spend most of your time with `db_volume_*` once a volume already exists.

## Which Function to Use

This table is focused on filesystem operations inside an existing volume:

Operation | Scope | Function | Notes
--- | --- | --- | ---
Upload file | Single file | `db_volume_write()` | Upload one local file to a volume path
Download file | Single file | `db_volume_read()` | Download one volume file to local disk
Delete file | Single file | `db_volume_delete()` | Remove one file from a volume
Check file exists | Single file | `db_volume_file_exists()` | Returns `TRUE`/`FALSE`
List contents | Directory | `db_volume_list()` | Lists files/subdirectories for a directory
Create directory | Directory | `db_volume_dir_create()` | Creates target directory path
Check directory exists | Directory | `db_volume_dir_exists()` | Returns `TRUE`/`FALSE`
Delete directory | Directory | `db_volume_dir_delete()` | Use `recursive = TRUE` for non-empty directories
Upload directory | Bulk transfer | `db_volume_upload_dir()` | Parallel upload, `recursive = TRUE` includes subdirectories
Download directory | Bulk transfer | `db_volume_download_dir()` | Parallel download, `recursive = TRUE` includes subdirectories

## Example Workflows

### Single File Round-Trip

If you just need to move one file in and out of a volume. This example goes beyond the minimum to showcase more than just upload/download.

    library(brickster)

    volume_root <- "/Volumes/zacdav/default/data"
    incoming_dir <- file.path(volume_root, "incoming")
    incoming_file <- file.path(incoming_dir, "example.csv")

    # create local file
    local_file <- tempfile(fileext = ".csv")
    write.csv(mtcars, local_file, row.names = FALSE)

    # ensure target directory exists
    db_volume_dir_create(incoming_dir)

    # upload file
    db_volume_write(
      path = incoming_file,
      file = local_file,
      overwrite = TRUE
    )

    # verify + inspect
    db_volume_file_exists(incoming_file)
    db_volume_list(incoming_dir)

    # download file back to local path
    downloaded_file <- tempfile(fileext = ".csv")
    db_volume_read(
      path = incoming_file,
      destination = downloaded_file
    )

    # verify that file can be read as csv
    read.csv(downloaded_file)

    # clean up (optional)
    db_volume_delete(incoming_file)
    db_volume_dir_delete(incoming_dir)

### Bulk Directory Transfer (Upload + Download)

This is a compact pattern for a larger transfer: sample a local dataset to 100 million rows, write a 2-level partitioned Arrow dataset, upload it, then download it back.

    library(brickster)
    library(arrow)
    library(dplyr)

    volume_root <- "/Volumes/zacdav/default/data"
    landing_dir <- file.path(volume_root, "sample_10m")
    local_dir <- tempfile("arrow_sample_")

    # sample to 10M rows
    # write partitioned Arrow dataset (2 levels deep: cyl/gear)
    mtcars |>
      sample_n(size = 1e+07, replace = TRUE) |>
      write_dataset(
        path = local_dir,
        format = "parquet",
        partitioning = c("cyl", "gear")
      )

    # bulk upload
    db_volume_upload_dir(
      local_dir = local_dir,
      volume_dir = landing_dir,
      overwrite = TRUE,
      recursive = TRUE
    )

    # bulk download
    local_download <- tempfile("arrow_download_")
    db_volume_download_dir(
      volume_dir = landing_dir,
      local_dir = local_download,
      overwrite = TRUE,
      recursive = TRUE
    )
    list.files(local_download, recursive = TRUE)

    # cleanup example directory recursively (optional)
    db_volume_dir_delete(
      path = landing_dir,
      recursive = TRUE
    )

Set `recursive = FALSE` for non-recursive transfer: only files directly under the source directory are transferred, and nested subdirectories are skipped.

## Managing Volume Objects (Optional)

Use `db_uc_volumes_*` when you need to create or manage the volume object itself (not files inside it).

Operation | Function | Notes
--- | --- | ---
List volumes in schema | `db_uc_volumes_list()` | Returns volumes under `<catalog>.<schema>`
Get one volume | `db_uc_volumes_get()` | Returns metadata for one volume
Create volume | `db_uc_volumes_create()` | Supports `MANAGED` and `EXTERNAL`
Update volume metadata | `db_uc_volumes_update()` | Rename/comment/owner updates
Delete volume | `db_uc_volumes_delete()` | Removes the Unity Catalog volume object

    # list volumes in a schema
    db_uc_volumes_list(catalog = "<catalog>", schema = "<schema>")

    # create a managed volume
    db_uc_volumes_create(
      catalog = "<catalog>",
      schema = "<schema>",
      volume = "my_volume",
      volume_type = "MANAGED"
    )

    # inspect one volume
    db_uc_volumes_get(
      catalog = "<catalog>",
      schema = "<schema>",
      volume = "my_volume"
    )

After a volume exists, use `/Volumes/<catalog>/<schema>/<volume>/...` paths with `db_volume_*` for file operations.