Fabric API - Files

onelake_list, onelake_read, onelake_write and onelake_delete, and the two forms a file path takes.

The four methods below read and write files in OneLake, the storage behind every lakehouse, and the Files section in the lakehouse explorer is the folder they work in.

File paths

Every path starts with the lakehouse and continues into it, and the lakehouse can be named in two ways:

Form	Example
Name and type	`Operations.Lakehouse/Files/incoming/invoices-2026-08.csv`
Item ID	`73811955-064d-481a-a7e9-f9c563124f9e/Files/incoming/invoices-2026-08.csv`

Both forms work in every method below. A lakehouse keeps files under Files, and the table methods write to Tables, next to it.

onelake_list

conn.onelake_list(workspace_id, directory='')

Lists the files and subfolders directly under a path.

Parameter	Type	Meaning
`workspace_id`	str	The workspace whose storage to list
`directory`	str	The folder to list, e.g. `Operations.Lakehouse/Files/incoming`, or empty for the top of the workspace

Returns a dict with paths, a list of dicts each with name (the full path), isDirectory (true or false), contentLength and lastModified.

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class ListFiles(Service):

    def handle(self):

        workspace_id = '262ddd3d-3d0d-4495-b80f-6dddda1e23a1'

        conn = self.microsoft.fabric['Zato Fabric']

        listing = conn.onelake_list(workspace_id, 'Operations.Lakehouse/Files/incoming')

        files = []
        for path in listing['paths']:
            file = {'name': path['name'], 'is_directory': path['isDirectory']}
            files.append(file)

        self.response.payload = {'files': files}

{"files": [{"name": "Operations.Lakehouse/Files/incoming/invoices-2026-08.csv", "is_directory": false}]}

onelake_read

conn.onelake_read(workspace_id, file_path)

Returns a file's contents as bytes.

Parameter	Type	Meaning
`workspace_id`	str	The workspace the file is in
`file_path`	str	The file, in either path form

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class ReadFile(Service):

    def handle(self):

        workspace_id = '262ddd3d-3d0d-4495-b80f-6dddda1e23a1'
        file_path = 'Operations.Lakehouse/Files/incoming/invoices-2026-08.csv'

        conn = self.microsoft.fabric['Zato Fabric']

        data = conn.onelake_read(workspace_id, file_path)
        text = data.decode('utf-8')

        size = len(data)
        lines = text.splitlines()
        first_line = lines[0]

        self.response.payload = {'size': size, 'first_line': first_line}

{"size": 142, "first_line": "invoice_id,location,insurer,amount,status,sent_at"}

onelake_write

conn.onelake_write(workspace_id, file_path, data)

Creates a file with these contents, or replaces it if it exists. Missing folders in the path are created.

Parameter	Type	Meaning
`workspace_id`	str	The workspace to write to
`file_path`	str	The file, in either path form
`data`	bytes, str or list of dicts	The contents - bytes go as they are, text is written as UTF-8, a list of dicts becomes CSV with a header made of the first row's keys

Returns nothing.

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class WriteFile(Service):

    def handle(self):

        workspace_id = '262ddd3d-3d0d-4495-b80f-6dddda1e23a1'
        file_path = 'Operations.Lakehouse/Files/exports/invoices-2026-08.csv'

        conn = self.microsoft.fabric['Zato Fabric']

        rows = [
          {'location': 'Riverside',   'invoiced': 2895.50},
          {'location': 'Oak Hill',    'invoiced': 1840.00},
          {'location': 'Maple Grove', 'invoiced': 415.75},
        ]

        conn.onelake_write(workspace_id, file_path, rows)

        self.response.payload = {'rows': len(rows)}

onelake_delete

conn.onelake_delete(workspace_id, file_path, recursive=False)

Deletes a file, or a folder with everything in it.

Parameter	Type	Meaning
`workspace_id`	str	The workspace the file is in
`file_path`	str	The file or folder, in either path form
`recursive`	bool	`True` to delete a folder along with its files and subfolders

Returns nothing. Deleting a file that does not exist raises an exception, as does deleting a non-empty folder without recursive.

# -*- coding: utf-8 -*-

# Zato
from zato.server.service import Service

class DeleteFile(Service):

    def handle(self):

        workspace_id = '262ddd3d-3d0d-4495-b80f-6dddda1e23a1'
        file_path = 'Operations.Lakehouse/Files/incoming/invoices-2026-08.csv'

        conn = self.microsoft.fabric['Zato Fabric']

        conn.onelake_delete(workspace_id, file_path)

Page	What it covers
Fabric API - Tables	Importing a written file into a table with load_table
Writing data to Fabric	Loading a file into a table and writing a monthly export
Fabric API - Connection	The storage token these methods use