ref() function for model dependencies in dbt

Introduction

The ref() function helps connect different data models in dbt. It makes sure models run in the right order and use the correct data.

When you want one data model to use the output of another model.

When you need dbt to understand the order to build your models.

When you want to avoid hardcoding table names and keep your project flexible.

When you want to easily track dependencies between models in your project.

Syntax

dbt

select * from {{ ref('model_name') }}

The ref() function takes the name of another model as a string.

It returns the correct table name or view for that model, depending on your dbt setup.

Examples

This selects all data from the customers model.

dbt

select * from {{ ref('customers') }}

This selects specific columns from the orders model.

dbt

select order_id, customer_id from {{ ref('orders') }}

This uses ref() inside a common table expression (CTE) to filter recent orders.

dbt

with recent_orders as (
  select * from {{ ref('orders') }} where order_date > '2024-01-01'
)
select * from recent_orders

Sample Program

This example shows three models. The customer_orders.sql model uses ref() to get data from customers and orders. It joins them to list recent orders with customer names.

dbt

/* Model: customers.sql */
select
  id as customer_id,
  name
from raw.customers

/* Model: orders.sql */
select
  id as order_id,
  customer_id,
  order_date
from raw.orders

/* Model: customer_orders.sql */
select
  c.customer_id,
  c.name,
  o.order_id,
  o.order_date
from {{ ref('customers') }} c
join {{ ref('orders') }} o on c.customer_id = o.customer_id
where o.order_date > '2024-01-01'
order by o.order_date desc

Important Notes

Always use ref() instead of hardcoding table names to keep your project flexible.

dbt uses ref() to build a dependency graph and run models in the right order.

If you rename a model, ref() helps avoid errors by updating references automatically.

Summary

ref() links models so dbt knows their order and dependencies.

It helps avoid hardcoding table names and keeps your project flexible.

Use ref() whenever you want one model to use another model's data.

Practice

1. What is the main purpose of the ref() function in dbt?

easy

A. To create new database users

B. To write raw SQL queries inside dbt models

C. To link models and define dependencies between them

D. To schedule dbt runs automatically

Solution

1. Step 1: Understand the role of ref()

   The ref() function is used to link one model to another in dbt, so dbt knows the order to run models and their dependencies.

2. Step 2: Identify what ref() does not do

   It does not write raw SQL, create users, or schedule runs. Its main role is linking models.

3. Final Answer:

   To link models and define dependencies between them -> Option C

4. Quick Check:

   ref() links models = A [OK]

Hint: Remember: ref() connects models, not SQL or users [OK]

Common Mistakes:

• Thinking ref() writes SQL code
• Confusing ref() with scheduling tools
• Assuming ref() manages database users

2. Which of the following is the correct syntax to reference a model named customers inside another model using ref()?

easy

A. select * from {{ ref('customers') }}

B. select * from ref('customers')

C. select * from ref(customers)

D. select * from {{ ref(customers) }}

Solution

1. Step 1: Recall dbt Jinja syntax for ref()

   In dbt, ref() must be wrapped in double curly braces and the model name must be a string in quotes.

2. Step 2: Check each option

   select * from {{ ref('customers') }} uses {{ ref('customers') }} which is correct. Options B and C miss the curly braces or quotes. select * from {{ ref(customers) }} misses quotes around the model name.

3. Final Answer:

   select * from {{ ref('customers') }} -> Option A

4. Quick Check:

   Use {{ ref('model_name') }} syntax = A [OK]

Hint: Always use {{ ref('model_name') }} with quotes and braces [OK]

Common Mistakes:

• Omitting curly braces {{ }}
• Not putting model name in quotes
• Using ref() without Jinja syntax

3. Given the following dbt model code, what will be the output SQL after compilation if the orders model exists?

select order_id, customer_id
from {{ ref('orders') }}

medium

A. select order_id, customer_id from orders

B. select order_id, customer_id from {{ ref('orders') }}

C. select order_id, customer_id from dbt.orders

D. select order_id, customer_id from ref('orders')

Solution

1. Step 1: Understand what ref() compiles to

   The ref() function compiles to the actual table name of the referenced model, usually just the model name like 'orders'.

2. Step 2: Check the compiled SQL output

   The compiled SQL replaces {{ ref('orders') }} with orders, so the output is select order_id, customer_id from orders.

3. Final Answer:

   select order_id, customer_id from orders -> Option A

4. Quick Check:

   ref('orders') compiles to orders = C [OK]

Hint: ref() compiles to the model's table name without braces [OK]

Common Mistakes:

• Leaving ref() uncompiled in SQL
• Adding extra schema prefix without config
• Using ref() as a string literal

4. You wrote this dbt model code:

select * from ref('sales')

When you run dbt, you get an error. What is the problem?

medium

A. Quotes around 'sales' should be removed

B. Model name 'sales' does not exist

C. ref() cannot be used inside select statements

D. Missing double curly braces around ref()

Solution

1. Step 1: Check the syntax of ref() usage

   In dbt, ref() must be wrapped in double curly braces to be interpreted as Jinja code.

2. Step 2: Identify the error cause

   The code uses ref('sales') without {{ }}, so dbt treats it as plain text, causing an error.

3. Final Answer:

   Missing double curly braces around ref() -> Option D

4. Quick Check:

   Use {{ ref('model') }} not ref('model') alone = D [OK]

Hint: Always wrap ref() in {{ }} to avoid errors [OK]

Common Mistakes:

• Forgetting {{ }} around ref()
• Assuming ref() works without Jinja
• Removing quotes from model name

5. You have two models: customers and orders. You want to create a new model customer_orders that joins these two. Which is the best way to use ref() to ensure correct dependencies and flexible naming?

hard

A. select c.customer_id, o.order_id from customers c join orders o on c.customer_id = o.customer_id

B. select c.customer_id, o.order_id from {{ ref('customers') }} c join {{ ref('orders') }} o on c.customer_id = o.customer_id

C. select c.customer_id, o.order_id from 'customers' c join 'orders' o on c.customer_id = o.customer_id

D. select c.customer_id, o.order_id from ref('customers') c join ref('orders') o on c.customer_id = o.customer_id

Solution

1. Step 1: Use ref() with correct Jinja syntax for both models

   To link models and ensure dbt knows dependencies, use {{ ref('model_name') }} for both customers and orders.

2. Step 2: Avoid hardcoding table names or missing Jinja syntax

   Options A and C hardcode names or use quotes incorrectly. select c.customer_id, o.order_id from ref('customers') c join ref('orders') o on c.customer_id = o.customer_id misses curly braces, so it won't compile.

3. Final Answer:

   select c.customer_id, o.order_id from {{ ref('customers') }} c join {{ ref('orders') }} o on c.customer_id = o.customer_id -> Option B

4. Quick Check:

   Use {{ ref('model') }} for all dependencies = B [OK]

Hint: Use {{ ref('model') }} for all model references [OK]

Common Mistakes:

• Hardcoding table names instead of using ref()
• Forgetting curly braces around ref()
• Using quotes incorrectly around model names