ref() function for model dependencies in dbt - Step-by-Step Execution

Concept Flow - ref() function for model dependencies

Start: Model A

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Call ref('Model B')

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dbt finds Model B

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Build dependency graph

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Run Model B first

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Run Model A after Model B

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Complete execution

The ref() function tells dbt which models depend on others, so it builds and runs them in the right order.

Execution Sample

dbt

select * from {{ ref('customers') }}
where active = true

This code uses ref() to get data from the 'customers' model before filtering active ones.

Execution Table

Step	Action	Input	Output	Notes
1	Start building 'orders' model	orders model SQL with ref('customers')	Detect dependency on 'customers'	ref() identifies 'customers' as dependency
2	Check if 'customers' model is built	Dependency graph	Not built yet	Must build 'customers' first
3	Build 'customers' model	customers model SQL	Table/view created	Customers data ready
4	Build 'orders' model	orders model SQL with ref resolved	Table/view created	Orders built using customers data
5	Execution complete	-	-	All models built in correct order

💡 All dependent models built; ref() resolved dependencies correctly

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
dependency_graph	empty	contains 'customers'	checks 'customers' built	adds 'customers' built	adds 'orders' built	complete
model_status	none built	'customers' needed	'customers' building	'customers' built	'orders' building	all built

Key Moments - 2 Insights

Why does dbt build the 'customers' model before 'orders'?

Because the 'orders' model uses ref('customers'), dbt knows 'orders' depends on 'customers' and builds 'customers' first (see execution_table step 2 and 3).

What happens if you forget to use ref() and just write the table name?

dbt won't know about the dependency, so it might build models in the wrong order, causing errors or stale data (reflected in dependency_graph variable_tracker).

Visual Quiz - 3 Questions

Look at the execution_table, at which step does dbt start building the 'customers' model?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Check the 'Action' column in execution_table for when 'customers' model is built.

According to variable_tracker, what is the state of 'model_status' after Step 3?

A 'orders' building

B 'customers' built

C none built

D 'customers' needed

💡 Hint

Look at the 'model_status' row and the column 'After Step 3' in variable_tracker.

If you remove ref('customers') from 'orders' model, what likely happens?

A dbt builds both models simultaneously without issues

B dbt ignores 'orders' model

C dbt builds 'orders' before 'customers' causing errors

D dbt automatically detects dependency anyway

💡 Hint

Recall key_moments about missing ref() causing wrong build order.

Concept Snapshot

ref('model_name') tells dbt which models depend on others.
It builds a dependency graph to run models in correct order.
Always use ref() to link models, not raw table names.
This ensures data freshness and avoids build errors.

Full Transcript

The ref() function in dbt is used to declare dependencies between models. When a model uses ref('other_model'), dbt knows it must build 'other_model' first. This creates a dependency graph that dbt uses to run models in the right order. For example, if 'orders' model uses ref('customers'), dbt builds 'customers' before 'orders'. This prevents errors and ensures data is fresh. If ref() is missing, dbt might build models in the wrong order, causing problems. The execution table shows each step: detecting dependencies, building dependent models, and completing execution. The variable tracker shows how the dependency graph and model statuses change step-by-step. Remember to always use ref() to link models in dbt projects.