workspace/skills/dbt-create-mart/SKILL.md

name, description

name	description
dbt_create_mart	Step-by-step instructions for creating dbt Mart models (facts and dimensions) as thin wrappers over transform models. Use for any dbt + Snowflake project.

Create a dbt Mart Model (Fact or Dimension)

Mart models are thin wrappers over transform models. They expose clean, BI-ready tables without duplicating business logic.

---

Fact Model Steps

1. Name the file

• Pattern: fct_<domain>_<metric>.sql
• Example: fct_sales_orders.sql, fct_ar_open_items.sql
• Lives in models/marts/facts/

2. Write a thin SELECT wrapper

Option A — expose all columns (most common):

select {{ dbt_utils.star(ref('<trf_model_name>')) }}
from {{ ref('<trf_model_name>') }}

Option B — add a light filter or derived column:

select
    *,
    <derived_column> as <alias>
from {{ ref('<trf_model_name>') }}
where <filter_condition>

3. Materialization

• Default: view (inherited from dbt_project.yml).
• Override to table only if the BI tool performs poorly on views.

---

Dimension Model Steps

1. Name the file

• Pattern: dim_<entity>.sql
• Example: dim_customers.sql, dim_materials.sql
• Lives in models/marts/dim/

2. Write the SELECT

• Dimensions are usually deduped/distinct entity lists from staging or transform.

select distinct
    <natural_key>          as <entity>_key,
    <descriptive_field_1>,
    <descriptive_field_2>
from {{ ref('<stg_or_trf_model>') }}
where <natural_key> is not null

3. Add schema entry

• File: models/marts/schema.yml
• Every fact: test unique + not_null on the primary key.
• Every dimension: test unique + not_null on the surrogate/natural key.
• Add relationships tests on foreign keys in fact models.

---

Rules

Rule	Detail
No business logic	Mart = wrapper only; logic belongs in transform
Materialization	view by default; table only if needed for BI performance
Column naming	snake_case for marts; inherit from the transform model
ref() only	Always reference the transform model with {{ ref() }}
BI-facing names	Rename columns here if the BI layer needs friendlier names

---

Templates

See mart_fct_template.sql and mart_dim_template.sql in this folder.