Model Contracts: Enforcing Shape at Build Time

# Model Contracts: Enforce Shape at Build Time Generic tests (`unique`, `not_null`) check data after it lands. Contracts reject bad builds before they land. ```yaml models: - name: mart_daily_revenue config: contract: enforced: true columns: - name: day data_type: date constraints: [not_null] - name: revenue_cents data_type: numeric constraints: [not_null] ``` ## Rules 1. **Contract the marts, not every staging model.** Enforce at the boundary consumers read (marts); keep staging flexible for messy sources. 2. **Constraints are the executable half of the contract:** `not_null`, `primary_key`, `foreign_key`, `check`. dbt renders them as real DDL on supported warehouses. 3. **A contract break fails `dbt build`.** That is the point — a renamed column or widened type stops the pipeline instead of silently shifting a dashboard. 4. **Warehouse support varies** (BigQuery/Snowflake/Databricks enforce; Postgres adapter renders constraints). Know your engine before promising enforcement.