Tag: artificial-intelligence

Building a Data Pipeline Using VSCode and Claude Out of Thin Air

A complete data pipeline running on Microsoft Fabric that downloads public data, transforms it into a star schema, exports it as Delta Lake tables, and serves it through a Power BI semantic model with Direct Lake — all from a single Python notebook and using pure SQL

all the code is available in github

and Interactive DAG

The entire stack:

  • One Fabric notebook (2 cells)
  • DuckDB as the compute engine — could have been Polars or Lakesail, just a personal preference to be honest
  • dbt as the transformation framework
  • A Python script to deploy everything via Fabric REST API
  • GitHub for source control, documentation, and testing

Note: DuckDB is not officially supported by Microsoft Fabric. Every effort is made to ensure compatibility with OneLake.

Overall Architecture

Why DuckDB + Delta Export

Microsoft Fabric’s lakehouse uses Delta Lake or Apache Iceberg as its table format. Power BI’s Direct Lake mode reads the data directly from OneLake. So whatever engine you use, you need to produce Delta Lake files on OneLake.

DuckDB cannot write Delta Lake natively (it is experimental at this stage). It has its own table format via the DuckLake extension, but DuckLake writes Parquet files with a DuckDB/SQLite/PostgreSQL metadata catalog.

OneLake catalog has only Iceberg read support, so that’s not an option for now.

The solution: delta_export, a community DuckDB extension that exports DuckLake tables as Delta Lake. The pipeline works like this:

  1. dbt transforms data into DuckLake tables (Parquet + metadata)
  2. ducklake_rewrite_data_files and ducklake_merge_adjacent_files compact the Parquet files
  3. CALL delta_export() converts every DuckLake table into a proper Delta Lake table on OneLake

Without delta_export, DuckLake is not useful in this context. DuckLake manages tables internally, but Fabric has no idea what a SQLite metadata catalog is. It needs Delta transaction logs.

From dbt_project.yml:

on-run-end:
  - "CALL ducklake_rewrite_data_files('ducklake')"
  - "CALL ducklake_merge_adjacent_files('ducklake')"
  - "CALL delta_export()"

DuckLake: How It Works and Its Limitations

DuckLake stores table metadata in a database and writes data as Parquet files to any storage backend (local, S3, Azure). The DuckDB connection looks like this:

# profiles.yml (prod target)
attach:
  - path: "ducklake:sqlite:{{ env_var('METADATA_LOCAL_PATH') }}"
    alias: ducklake
    options:
      data_path: "{{ env_var('ROOT_PATH') }}/Tables"
      data_inlining_row_limit: 0

METADATA_LOCAL_PATH points to /lakehouse/default/Files/metadata.db — the Files section of the OneLake lakehouse. In a Fabric notebook, /lakehouse/default/ is a local mount of the lakehouse storage. The SQLite file lives right there on OneLake, persisting across notebook runs without any special sync logic. data_path points to the Tables section on OneLake (abfss://...). DuckDB computes in memory, DuckLake tracks what’s in each table via SQLite, and Parquet files land on OneLake.

The single-writer limitation. DuckLake when used with a file-based DB is basically a single-writer architecture. Only one process can write to a DuckLake database at a time. This means:

  • No parallel pipeline runs
  • No concurrent notebooks writing to the same tables
  • The Fabric pipeline is set to concurrency: 1 specifically because of this

For this use case, it’s fine — one notebook runs every hour, processes new files, and exits. But if you need concurrent writers, DuckLake is not the right choice.

Obviously you can use PostgreSQL as a catalog, but that makes the architecture more complex.

dbt as the Orchestrator

dbt does everything here — not just transformations. The on-run-start hook downloads data from the web, archives it to OneLake, and tracks state in a parquet log. The on-run-end hook compacts files and exports Delta.

on-run-start:
  - "CALL ducklake.set_option('rewrite_delete_threshold', 0)"
  - "CALL ducklake.set_option('target_file_size', '128MB')"
  - "{{ download() }}"
on-run-end:
  - "CALL ducklake_rewrite_data_files('ducklake')"
  - "CALL ducklake_merge_adjacent_files('ducklake')"
  - "CALL delta_export()"

The download() macro (371 lines) handles:

  • Fetching daily SCADA and price reports from AEMO’s website
  • Fetching intraday 5-minute dispatch data
  • Downloading generator reference data
  • Archiving everything as partitioned ZIPs on OneLake
  • Maintaining a csv_archive_log.parquet file for deduplication

The 8 dbt models then process this data:

  • stg_csv_archive_log — view over the archive log
  • dim_calendar — date dimension (one-time load)
  • dim_duid — generator unit reference (smart refresh: only rebuilds when new generators appear)
  • fct_scada, fct_price — daily historical data, incremental by file
  • fct_scada_today, fct_price_today — intraday data, incremental by file
  • fct_summary — combined fact table exposed to Power BI

Every fact model uses file-based incremental processing. Pre-hooks query the archive log, filter out already-processed files, and set DuckDB VARIABLEs with the remaining ZIP paths. The model’s SQL reads from those paths. Next run, those files are skipped.

The Semantic Model: AI-Generated from Thin Air

This is the part that surprises me the most. The model.bim file — the Power BI semantic model definition — was generated entirely by AI (Claude). No Power BI Desktop. No click-through wizards. No SSDT.

The model.bim is a JSON file in TMSL (Tabular Model Scripting Language) format. It defines:

  • 3 tables exposed to Power BI: dim_calendar, dim_duid, fct_summary
  • 5 hidden tables (raw layer, not needed for reporting)
  • 2 relationships (fact → dimension)
  • 5 DAX measures (Total MW, Total MWh, Avg Price, Generator Count, Latest Update)
  • Direct Lake partitions pointing to Delta tables on OneLake

Notice I am using pure Direct Lake mode that does not fall back to SQL:

{
  "name": "PBI_ProTooling",
  "value": "[\"RemoteModeling\", \"DirectLakeOnOneLakeCreatedInDesktop\"]"
}

The M expression for the data source:

let
    Source = AzureStorage.DataLake("{{ONELAKE_URL}}", [HierarchicalNavigation=true])
in
    Source

{{ONELAKE_URL}} is a placeholder. The deploy script substitutes it with the actual OneLake URL at deploy time.

Each table partition maps to a Delta table on OneLake:

{
  "mode": "directLake",
  "source": {
    "type": "entity",
    "entityName": "fct_summary",
    "expressionSource": "DirectLake",
    "schemaName": "aemo"
  }
}

This maps to Tables/aemo/fct_summary/ — exactly where DuckLake + delta_export writes the Delta files.

AI generated all of this by reading the dbt schema definitions (column names, types, descriptions) and understanding the Direct Lake requirements. No manual TMSL authoring. No reverse engineering from Power BI Desktop. The entire semantic model is version-controlled, diffable, and deployable via API.

Poor Man CI/CD, No Service Principal

deploy_to_fabric.py is a single Python script that deploys everything to Fabric using the REST API. It has 6 steps:

  1. lakehouse — Create the OneLake lakehouse (with schema support)
  2. files — Upload all dbt project files to Files/dbt/
  3. notebook — Create a 2-cell notebook (install deps + run dbt)
  4. pipeline — Create a pipeline that runs the notebook
  5. schedule — Set up hourly cron schedule
  6. semantic_model — Deploy model.bim with Direct Lake config + refresh

You can run any subset: python deploy_to_fabric.py semantic_model deploys just the BIM.

Authentication uses az login — your browser opens, you sign in, done. The script reads from the production git branch (clones it into a temp directory) so what you deploy is always what’s been merged to production.

python deploy_to_fabric.py              # deploy everything
python deploy_to_fabric.py semantic_model   # just the semantic model
python deploy_to_fabric.py files notebook   # just files + notebook

and here is the script in action

CI/CD

assuming you got pass the app registration in Azure, GitHub Actions handles CI — on every push and pull request to production:

Q&A

Why deploy to Fabric from local instead of from GitHub Actions?

CI (testing, docs, DAG) runs in GitHub Actions — no cloud credentials needed, just Azurite. But Fabric deployment requires authenticating to the Fabric REST API, which means a service principal.

This is just my personal experience working in different companies. As a business user, there is almost zero chance IT will give permission to register an app. And even if a miracle happens, you still need to convince a Fabric admin. This is not a technical limitation, it is human behaviour.

Instead, deploy_to_fabric.py uses AzureCliCredential — you run az login, your browser opens, you sign in, done. The script picks up your existing identity. You already have the Fabric permissions. No secrets to store, no service principal to manage.

The tradeoff is that deployment requires a human at a keyboard. For a single-person or small-team project, that’s fine — you deploy when you’re ready, not on every push.

Why not just use Datawarehouse/Spark/Dataflow etc? It’s built into Fabric.

All those tools in Fabric are awesome, but it is a lakehouse and the whole point of a lakehouse is to use whatever you want as long as it produces Parquet and Delta/Iceberg metadata, ideally sorted with a decent row group size from 2M to 16M.

Why DuckLake instead of Delta or Iceberg?

  • DuckDB Delta write support is still experimental.
  • OneLake Catalog supports Iceberg read only.

If we had Iceberg write, that would be my first preference.

Why is the semantic model AI-generated?

Because it is cool 🙂 and it is unbelievable that AI managed to write it out of thin air and did cool stuff like generating descriptions so Power BI AI behaves better.

What happens if the pipeline fails mid-run?

The DuckLake metadata DB lives on OneLake (Files section). If the run fails mid-way:

  • Downloaded source files are already archived on OneLake (no re-download needed)
  • DuckLake metadata reflects whatever was committed before the failure
  • Next run picks up where it left off using the archive log

The pipeline has a 1-hour timeout. If it hangs, Fabric kills it and the next hourly run starts fresh.

Can this scale?

Python notebooks scale to half a TB of RAM. If you need more, then you are reading the wrong blog 🙂

Where is TMDL?

I could not deploy using TMDL, even after feeding AI all kurt buhler articles 🙂 bim seems to be better undersood at least for now.

Why use SQLite instead of DuckDB to store the metadata DB?

The Files section of OneLake is not a real POSIX filesystem. It is not like your local disk — it basically uses FUSE. All Python engines think it is a real filesystem, but I noticed SQLite works better than DuckDB for this. It flushes data more reliably.

What is skill

In this case, a skill is simply a way to capture what was learned during the work so the AI can reuse that knowledge later.

I wrote the skill after finishing the task, then asked the AI to summarize the key learnings and steps. The idea is that next time the AI runs a similar task, it will be better informed and produce better results.

This is not specific to Claude. The same approach works with Copilot as well. The format is different, but the idea is exactly the same: capture the knowledge once so the AI can reuse it later.

Parting Thoughts

Everything you have heard about AI is pretty much true. The only wrong part was the timing. We all knew about AI’s potential, but in my experience something changed around December 2025. Suddenly AI became genuinely useful — less hallucination, and it just works well enough. Especially when you can test the outcome. And that is the key insight: data engineering is, in a sense, just software engineering. AI writes the code, AI does everything. Your job as a user is to make sure the tests are comprehensive. Contrary to what you hear from professional software engineers, you don’t need to care about the general case. If it is solid enough and it works for your use case, that is all that matters. Nothing more.

There is another aspect worth mentioning. There is a real market for business users who are not programmers. There is enormous value in using your laptop as your main dev and test environment. You open VSCode, you talk to your favorite AI agent, you run dbt run, and you see results in seconds. That feedback loop changes everything. Data platforms like Fabric become a hosting environment with security boundaries, governance, and all that.

and if you are still reading, dbt test are just awesome !!!

Python Engines current Onelake Catalog integration

Same 22 TPC-H queries. Same Delta Lake data on OneLake (SF10). Same single Fabric node. Five Python SQL engines: DuckDB (Delta Classic), DuckDB (Iceberg REST), LakeSail, Polars, DataFusion , you can download the notebook here

unfortunately both daft and chdb did not support reading from Onelake abfss

DuckDB iceberg read support is not new, but it is very slow, but the next version 1.5 made a massive improvements and now it is slightly faster than Delta

They all run the same SQL now

All five engines executed the exact same SQL. No dialect tweaks, no rewrites. The one exception: Polars failed on Query 11 with 

`SQLSyntaxError: subquery comparisons with '>' are not supported`

Everything else just worked,SQL compatibility across Python engines is basically solved in 2026. The differentiators are elsewhere.

Freshness vs. performance is a trade-off you should be making

import duckdb
conn = duckdb.connect()
conn.sql(f"""  install delta_classic FROM community  ;
attach 'abfss://{ws}@onelake.dfs.fabric.microsoft.com/{lh}.Lakehouse/Tables/{schema}'
AS db (TYPE delta_classic, PIN_SNAPSHOT); USE db
            """)

`MAX_TABLE_STALENESS ‘5 minutes’` means the engine caches the catalog metadata and skips the round-trip for 5 minutes.

DuckDB’s Delta Classic does the same with `PIN_SNAPSHOT`.

import duckdb
conn = duckdb.connect()
conn.sql(f"""  install delta_classic FROM community  ;
attach 'abfss://{ws}@onelake.dfs.fabric.microsoft.com/{lh}.Lakehouse/Tables/{schema}'
AS db (TYPE delta_classic, PIN_SNAPSHOT); USE db
            """)

Your dashboard doesn’t need sub-second freshness. Your reporting query doesn’t care about the last 30 seconds of ingestion. Declaring a staleness budget upfront – predictable, explicit – is not a compromise. It’s the right default for analytics.

Object store calls are the real bottleneck

Every engine reads from OneLake over ABFSS. Every Parquet file is a network call. It doesn’t matter how fast your engine scans columnar data in memory if it makes hundreds of HTTP calls to list files and read metadata before it starts.

– DuckDB Delta Classic (PIN_SNAPSHOT): caches the Delta log and file list at attach time. Subsequent queries skip the metadata round-trips.

– DuckDB Iceberg (MAX_TABLE_STALENESS): caches the Iceberg snapshot from the catalog API. Within the staleness window, no catalog calls.

– LakeSail: has native OneLake catalog integration (SAIL_CATALOG__LIST). You point it at the lakehouse, it discovers tables and schemas through the catalog. Metadata resolution is handled by the catalog layer, not by scanning storage paths, but it has no concept of cache, every query will call Onelake Catalog API

– Polars, DataFusion: resolve the Delta log on every query. Every query pays the metadata tax.

An engine that caches metadata will beat a “faster” engine that doesn’t. Every time, especially at scale.

How about writes?

You can write to OneLake today using Python deltalake or pyiceberg – that works fine. But native SQL writes (CREATE TABLE AS INSERT INTO ) through the engine catalog integration itself? That’s still the gap, lakesail can write delta just fine but using a path.

– LakeSail and DuckDB Iceberg both depend on OneLake’s catalog adding write support. The read path works through the catalog API, but there’s no write path yet. When it lands, both engines get writes for free.

– DuckDB Delta Classic has a different bottleneck: DuckDB’s Delta extension itself. Write support exists but is experimental and not usable for production workloads yet.

The bottom line

Raw execution speed will converge. These are all open source projects, developers read each other’s code, there’s no magical trick one has that others can’t adopt. The gap narrows with every release.

Catalog Integration and cache are the real differentiator. And I’d argue that even *reading* from OneLake is nearly solved now.

—

Full disclosure: I authored the DuckDB Delta Classic extension and the LakeSail OneLake integration (both with the help of AI), so take my enthusiasm for catalog integration with a grain of bias

Querying a Onelake Table with RLS and CLS Using DuckDB’s MSSQL Extension

Onelake supports Row Level Security and Column Level Security. These protections work when you use trusted engines such as Power BI or Spark running inside Microsoft Fabric. In those environments, the compute engine operates within a controlled boundary, so security rules can be enforced properly.

However, if you try to access the storage directly from a Python notebook or a local engine running on your laptop, including open source Spark, direct access is blocked. Otherwise, Row Level Security and Column Level Security would be meaningless. Security only works when the engine itself is trusted and governed.

This blog show a workaround by laveraging SQL Endpoint, These policies are enforced at the SQL endpoint, meaning any external tool that connects through it — including DuckDB — automatically respects them.

Let’s walk through a quick example.

The Data

We have a power.duid table containing 626 rows of Australian power generation facilities. Columns include DUID, Region, FuelSourceDescriptor, Participant, State, latitude, and longitude.

Configuring Row-Level Security

In the Lakehouse role readsometables, we add an RLS rule that restricts visibility to a single region:

SELECT * FROM power.duid WHERE Region='WA1'

Members of this role will only see rows where Region = 'WA1'.

Configuring Column-Level Security

On the same role, we enable CLS and grant Read visibility only to specific columns: DUID, Region, FuelSourceDescriptor, State, latitude, and longitude. The Participant column is excluded.

Querying with DuckDB’s MSSQL Extension

From any Python environment, we can connect to the SQL endpoint using DuckDB’s community MSSQL extension and Azure authentication:

import duckdb
from azure.identity import DefaultAzureCredential

conn = duckdb.connect()
token = DefaultAzureCredential().get_token("https://database.windows.net/.default").token

conn.sql(f"""
    ATTACH IF NOT EXISTS
    'Server=<your-sql-endpoint>;Database=data'
    AS data (TYPE mssql, ACCESS_TOKEN '{token}')
""")

if you are running it inside Fabric notebook, first you need to updgrade duckdb, 

!pip install duckdb --upgrade
import sys
sys.exit(0)

the run this code

import duckdb
conn = duckdb.connect()
token = notebookutils.credentials.getToken('sql')
conn.sql(f"""
                install mssql from community ;
                ATTACH if not exists
                'Server=SQL_endpoint;Database=data'
                AS data (TYPE mssql, ACCESS_TOKEN '{token}')
          """)



Now when we query, RLS and CLS are enforced server-side:

conn.sql("SELECT DISTINCT(Region) FROM data.power.duid").show()

Only WA1 — the RLS filter is working. And if we select all columns:

conn.sql("SELECT * FROM data.power.duid LIMIT 4").show()

you get an error, that you can not select Participant

No Participant column — CLS is doing its job, now if you remove it , everything works fine

First Look at Geometry Types in Parquet

Getting different parties in the software industry to agree on a common standard is rare. Most of the time, a dominant player sets the rules. Occasionally, however, collaboration happens organically and multiple teams align on a shared approach. Geometry types in Parquet are a good example of that.

In short: there is now a defined way to store GIS data in Parquet. Both Delta Lake and Apache Iceberg have adopted the standard ( at least the spec). The challenge is that actual implementation across engines and libraries is uneven.

  • Iceberg: no geometry support yet in Java nor Python, see spec
  • Delta:  it’s unclear if it’s supported in the  open source implementation (I need to try sedona and report back), nothing in the spec though ?
  • DuckDB: recently added support ( you need nightly build or wait for 1.4)
  • PyArrow: has included support for a few months, just use the latest release
  • Arrow rust : no support, it means, no delta python support 😦

The important point is that agreeing on a specification does not guarantee broad implementation. and even if there is a standard spec, that does not means the initial implementation will be open source, it is hard to believe we still have this situation in 2025 !!!

Let’s run it in Python Notebook

To test things out, I built a Python notebook that downloads public geospatial data, merges it with population data, writes it to Parquet, and renders a map using GeoPandas, male sure to install the latest version of duckdb, pyarrow and geopandas

!pip install -q duckdb  --pre --upgrade
!pip install -q pyarrow --upgrade
!pip install geopandas  --upgrade
import sys
sys.exit(0)

At first glance, that may not seem groundbreaking. After all, the same visualization could be done with GeoJSON. The real advantage comes from how geometry types in Parquet store bounding box coordinates. With this metadata, spatial filters can be applied directly during reads, avoiding the need to scan entire datasets.

That capability is what makes the feature truly valuable: efficient filtering and querying at scale, note that currently duckdb does not support pushing those filters, probably you need to wait to early 2026 ( it is hard to believe 2025 is nearly gone)

👉Workaround if your favorite Engine don’t support it .

 A practical workaround is to read the Parquet file with DuckDB (or any library that supports geometry types) and export the geometry column back as WKT text. This allows Fabric to handle the data, albeit without the benefits of native geometry support, For example PowerBI can read WKT just fine

duckdb.sql("select geom, ST_AsText(geom) as wkt  from '/lakehouse/default/Files/countries.parquet' ")

For PowerBI support to wkt, I have written some blogs before, some people may argue that you need a specialized tool for Spatial, Personally I think BI tools are the natural place to display maps data 🙂