working-with-dbt-mesh

Working with dbt Mesh

Core principle: In a mesh project, upstream data comes through ref(), not source(). Every cross-project reference requires the project name. When in doubt, read dependencies.yml first.

When to Use

• Working in a dbt project that references models from other dbt projects
• Resolving ambiguity when multiple upstream projects have similarly-named models (e.g. multiple stg_ models)
• Adding model contracts, access modifiers, groups, or versioning
• Setting up cross-project references with dependencies.yml
• Splitting a monolithic dbt project into multiple mesh projects

Do NOT use for:

• General model building or debugging (use the using-dbt-for-analytics-engineering skill)
• Unit testing models (use the adding-dbt-unit-test skill)
• Semantic layer work (use the building-dbt-semantic-layer skill)

First: Orient Yourself in a Multi-Project Setup

Before writing or modifying any SQL in a project that uses dbt Mesh, follow these steps:

1. Read dependencies.yml

This file at the project root tells you which upstream projects exist:

# dependencies.yml
projects:
  - name: core_platform
  - name: marketing_platform

If this file has a projects: key, you are in a multi-project mesh setup. Every model you reference from those upstream projects must use cross-project ref().

2. Understand how upstream data gets into this project

In a mesh setup, upstream project models replace what would alternatively be sources:

Alternative	Mesh multi-project
{{ source('stripe', 'payments') }}	{{ ref('core_platform', 'stg_payments') }}
Data comes from raw database tables	Data comes from another dbt project's public models
Defined in sources.yml	Declared in dependencies.yml

The upstream project has already staged and transformed the raw data. Your project builds on top of their public models, not their raw sources.

3. Disambiguate similarly-named models

When multiple upstream projects have models with the same name (e.g. stg_customers in both core_platform and marketing_platform), you must use the two-argument ref():

-- Correct: explicit project name, no ambiguity
select * from {{ ref('core_platform', 'stg_customers') }}
select * from {{ ref('marketing_platform', 'stg_customers') }}

-- WRONG: dbt cannot determine which project's stg_customers you mean
select * from {{ ref('stg_customers') }}

4. Check existing patterns in the codebase

Before writing new SQL:

• Search for existing two-argument ref() calls to see which upstream projects and models are already in use
• Look at the upstream project's YAML for access: public models — only these are referenceable cross-project
• The first argument of ref() must exactly match the name field in the upstream project's dbt_project.yml (case-sensitive)

5. Know what you can and cannot reference

Upstream model access	Can you ref() it cross-project?
access: public	Yes
access: protected (default)	No — only within the same project
access: private	No — only within the same group

If you need a model that isn't public, coordinate with the upstream team to widen its access.

Cross-Project Refs Require dbt Cloud Enterprise

Cross-project ref() and the projects: key in dependencies.yml are only available on dbt Cloud Enterprise or Enterprise+ plans. Before setting up any cross-project collaboration, verify plan eligibility:

1. If dependencies.yml already has a projects: key and the project is actively using cross-project refs — Enterprise is already in place. Proceed.
2. Otherwise — ask the user to confirm they are on dbt Cloud Enterprise or Enterprise+ before adding projects: to dependencies.yml or writing new two-argument ref() calls.

If the user cannot confirm the plan level, or confirms they are on a plan below Enterprise, do not set up cross-project refs. Explain that this feature requires upgrading to Enterprise or Enterprise+ and suggest they use the intra-project governance features (groups, access modifiers, contracts) instead.

Cross-Project ref() Syntax

-- Reference an upstream model (latest version)
select * from {{ ref('upstream_project', 'model_name') }}

-- Reference a specific version
select * from {{ ref('upstream_project', 'model_name', v=2) }}

For full cross-project setup details (dependencies.yml, prerequisites, orchestration), see references/cross-project-collaboration.md.

Governance Features

dbt Mesh includes four governance features. These work independently and can be adopted incrementally:

Feature	Purpose	Key Config	Reference
Model Contracts	Guarantee column names, types, and constraints at build time	contract: {enforced: true}	references/model-contracts.md
Groups	Organize models by team/domain ownership	group: finance	references/groups-and-access.md
Access Modifiers	Control which models can ref yours	access: public / protected / private	references/groups-and-access.md
Model Versions	Manage breaking changes with migration windows	versions: with latest_version:	references/model-versions.md

YAML placement rule

In model property YAML files, access, group, and contract are configs and must always be nested under the config: key — never placed as top-level model properties. Placing them at the top level may appear to work in dbt Core but causes parse errors in dbt's Fusion engine.

# ✅ CORRECT — all governance configs under `config:`
models:
  - name: fct_orders
    config:
      group: finance
      access: public
      contract:
        enforced: true
    columns:
      - name: order_id
        data_type: int

# ❌ WRONG — governance configs as top-level properties (breaks Fusion)
models:
  - name: fct_orders
    access: public          # WRONG — not under config:
    group: finance          # WRONG — not under config:
    contract:               # WRONG — not under config:
      enforced: true
    columns:
      - name: order_id
        data_type: int

This applies to property YAML files only. In dbt_project.yml, use the + prefix for directory-level assignment (e.g. +group: finance, +access: private). In SQL files, use {{ config(access='public', group='finance') }}.

Adoption order

1. Groups & Access  →  2. Contracts  →  3. Versions  →  4. Cross-Project Refs
   (organize teams)     (lock shapes)    (manage changes)  (split projects)

• Groups & Access — no schema changes needed, start here
• Contracts — require declaring every column and data type in YAML
• Versions — only needed when a contracted model must introduce a breaking change
• Cross-Project Refs — require dbt Cloud Enterprise or Enterprise+ and a successful upstream production job. Do not set up cross-project refs if you cannot confirm the plan level is Enterprise or higher.

Contracts vs. Tests

	Contracts	Data Tests
When	Build-time (pre-flight)	Post-build (post-flight)
What	Column names, data types, constraints	Data quality, business rules
Failure	Model does not materialize	Model exists but test fails
Use for	Shape guarantees for downstream consumers	Content validation and anomaly detection

Contracts are enforced before tests run. If a contract fails, the model is not built, and no tests execute.

Decision Framework

Should this model have a contract?

Use a contract when:

• The model is access: public (especially if referenced cross-project)
• Other teams depend on this model's schema stability
• The model feeds an exposure (dashboard, ML pipeline, reverse ETL)
• External consumers (other dbt projects, BI dashboards, reverse ETL) query the table directly and would break from column renames or removals

Do NOT add a contract when:

• Staging models (stg_*) — these are internal implementation details, not consumer-facing APIs
• The model is still evolving — if the user says they are iterating on the design, advise waiting until the schema stabilizes
• No external consumers exist — in a single-project setup with no cross-project refs, no BI tools depending on the schema, and no exposures, contracts add maintenance overhead without benefit. Ask about consumers before recommending contracts.
• Dynamic/pivot columns — models that use pivot(), unpivot(), or dynamically generate columns are poor candidates because the column list isn't fixed and the contract will break whenever the dynamic values change
• Ephemeral models — contracts are not supported on ephemeral materializations

If the user asks for a contract on a model that matches the "do NOT add" criteria above, advise against it and explain why. Do not simply comply — the user may not realize the contract is inappropriate. Suggest alternatives (e.g., data tests for staging models, waiting for schema stability, or switching materialization for ephemeral models).

Should this model be versioned?

Version a model when:

• It has an enforced contract AND you need to introduce a breaking change (column removal, rename, type change)
• Downstream consumers need a migration window before the old shape goes away

Do NOT version a model:

• For additive changes (new columns) — these are non-breaking
• For bug fixes — fix in place
• Preemptively "just in case" — version only when a breaking change is actually needed

What access level should this model have?

Is it referenced cross-project?
  └─ Yes → public (with contract recommended)
  └─ No
      Is it referenced outside its group?
        └─ Yes → protected (default)
        └─ No
            Is it internal to a small team?
              └─ Yes → private
              └─ No → protected (default)

Best practice: Default new models to private and widen access only when needed. The default protected is permissive — be intentional.

Common Mistakes

Mistake	Why It's Wrong	Fix
Using single-argument ref() in multi-project setups	Ambiguous — dbt may not resolve to the intended project	Always use ref('project_name', 'model_name') for cross-project refs
Using source() for upstream project data	In mesh, upstream data comes through public models, not raw sources	Use ref('upstream_project', 'model_name') instead
Not reading dependencies.yml first	You won't know which upstream projects exist or what they're called	Always read dependencies.yml before writing cross-project SQL
Making all models public	Exposes internal implementation details cross-project	Only mark models public that are intentional APIs for other teams
Skipping contracts on public models	Downstream consumers can break silently when schema changes	Always enforce contracts on access: public models
Versioning for non-breaking changes	Creates unnecessary maintenance burden and warehouse cost	Only version for breaking changes (column removal, type change, rename)
Forgetting dependencies.yml	Cross-project refs fail without declaring the upstream project	Add upstream project to dependencies.yml before using two-argument ref()
Referencing non-public models cross-project	Only public models are available to other projects	Set access: public on models intended for cross-project consumption
Placing access, group, or contract as top-level model properties in YAML	Breaks Fusion engine parsing; top-level placement is not valid config	Always nest under config: — e.g. config: { access: public }
Adding contracts to staging models	Staging models are internal — contracts add friction without protecting external consumers	Advise against it; suggest data tests instead
Adding contracts to models with dynamic/pivot columns	Column list changes with data, breaking the contract	Advise against it; explain why the column list isn't fixed
Adding contracts without establishing external consumers	Contracts protect a schema boundary — no consumers means no boundary to protect	Ask who depends on this model before adding a contract
Making a model private that is already referenced outside its group	Existing refs break with a DbtReferenceError	Widen access to protected or refactor callers into the same group first
Setting up cross-project refs without confirming dbt Cloud Enterprise	Cross-project ref() is unavailable on lower plan tiers	Confirm the plan level before adding projects: to dependencies.yml or writing two-argument ref() calls
Adding dependencies.yml without a successful upstream production job	dbt Cloud resolves cross-project refs via the upstream manifest.json — no job run means no manifest	Run at least one successful production deployment in the upstream project first