dbt Model Development

Read before you write. Build after you write. Verify your output.

Critical Rules

•ALWAYS run dbt build after creating/modifying models - compile is NOT enough
•ALWAYS verify output after build using dbt show - don't assume success
•If build fails 3+ times, stop and reassess your entire approach

Workflow

1. Understand the Task Requirements

•What columns are needed? List them explicitly.
•What is the grain of the table (one row per what)?
•What calculations or aggregations are required?

2. Discover Project Conventions

bash

cat dbt_project.yml
find models/ -name "*.sql" | head -20

Read 2-3 existing models to learn naming, config, and SQL patterns.

3. Find Similar Models

bash

# Find models with similar purpose
find models/ -name "*agg*.sql" -o -name "*fct_*.sql" | head -5

Learn from existing models: join types, aggregation patterns, NULL handling.

4. Check Upstream Data

bash

# Preview upstream data if needed
dbt show --select <upstream_model> --limit 10

5. Write the Model

Follow discovered conventions. Match the required columns exactly.

6. Compile (Syntax Check)

bash

dbt compile --select <model_name>

7. BUILD - MANDATORY

This step is REQUIRED. Do NOT skip it.

bash

dbt build --select <model_name>

If build fails:

•Read the error carefully
•Fix the specific issue
•Run build again
•If fails 3+ times, step back and reassess approach

8. Verify Output (CRITICAL)

Build success does NOT mean correct output.

bash

# Check the table was created and preview data
dbt show --select <model_name> --limit 10

Verify:

•Column names match requirements exactly
•Row count is reasonable
•Data values look correct
•No unexpected NULLs

9. Verify Calculations Against Sample Data

For models with calculations, verify correctness manually:

bash

# Pick a specific row and verify calculation by hand
dbt show --inline "
  select *
  from {{ ref('model_name') }}
  where <primary_key> = '<known_value>'
" --limit 1

# Cross-check aggregations
dbt show --inline "
  select count(*), sum(<column>)
  from {{ ref('model_name') }}
"

For example, if calculating total_revenue = quantity * price:

•Pick one row from output
•Look up the source quantity and price
•Manually calculate: does it match?

10. Re-review Against Requirements

Before declaring done, re-read the original request:

•Did you implement what was asked, not what you assumed?
•Are column names exactly as specified?
•Is the calculation logic correct per the requirements?
•Does the grain (one row per what?) match what was requested?

Anti-Patterns

•Declaring done after compile without running build
•Not verifying output data after build
•Getting stuck in compile/build error loops
•Assuming table exists just because model file exists
•Writing SQL without checking existing model patterns first