[staging] Throw error if model contract enforced

CHANGELOG.md

@@ -1,5 +1,8 @@
 ## dbt-databricks 1.5.0 (Release TBD)
 
+### Under the hood
+Throw an error if a model has an enforced contract. ([#322](https://github.com/databricks/dbt-databricks/pull/322))
+
 ## dbt-databricks 1.4.2 (February 17, 2023)
 
 ### Fixes

dbt/include/databricks/macros/adapters.sql

@@ -105,6 +105,12 @@
 {% endmacro %}
 
 {% macro databricks__persist_constraints(relation, model) %}
+  {# Model contracts are not currently supported. #}
+  {%- set contract_config = config.get('contract') -%}
+  {% if contract_config and contract_config.enforced %}
+    {{ exceptions.raise_compiler_error('Model contracts are not currently supported.') }}
+  {% endif %}
+
   {% if config.get('persist_constraints', False) and config.get('file_format', 'delta') == 'delta' %}
     {% do alter_table_add_constraints(relation, model.meta.constraints) %}
     {% do alter_column_set_constraints(relation, model.columns) %}

docs/databricks-dbt-constraints-vs-model-contracts.md

@@ -0,0 +1,98 @@
+# dbt-databricks constraints vs DBT 1.5 model contracts 
+
+dbt-databricks constraints are enabled for a model by setting  `persist_constraints: true`  in the model configuration.  Model contracts are enabled by setting `enforced: true` under the contract configuration.
+
+```
+models:
+  - name: table_model
+    config:
+      contract:
+        enforced: true
+```
+
+DBT model contracts enforce column names and datatypes.  This means that **all** columns must be explicitly listed and have name and data_type properties.
+
+dbt-databricks constraints list model level constraints under `meta: constraints:` while in DBT `constraints` is a property of the model.
+```
+dbt-databricks
+
+models:
+  - name: incremental_model
+    meta:
+      constraints:
+        - name: id_greater_than_zero
+          condition: id > 0
+```
+
+```
+model contract
+
+models:
+  - name: table_model
+    constraints:
+      - type: check
+        columns: [id]
+        name: id_greater_than_zero
+        expression: "id > 0"
+```
+
+dbt-databricks constraints have a single column level constraint (currently limited to not_null) defined by the `meta: constraint:`  property.
+Model contracts have multiple column constraints listed under a columns `constraints` property.
+```
+dbt-databricks
+
+    columns:
+      - name: name
+        meta:
+          constraint: not_null
+```
+
+```
+model contract
+
+    columns:
+      - name: name
+        data_type: string
+        constraints:
+          - type: not_null
+```
+
+Model contract constraint structure:
+- **type** (required): dbt-databricks constraints do not have this property. DBT has  not_null, check, primary_key, foreign_key, and custom types. dbt-databricks constraints currently support the equivalents of not_null and check.
+- **expression**: Free text input to qualify the constraint. In dbt-databricks constraints this is the  condition property. Note: in model contracts the expression text is contained by double quotes, the condition text in dbt-databricks constraints is not double quoted.
+- **name** (optional in model contracts, required for check constraints in dbt-databricks constraints): Human-friendly name for this constraint.
+- **columns** (model-level only): List of column names to apply the constraint over. dbt-databricks constraints do not have this property.
+
+
+ In a model contract a check constraint over a single column can be defined at either the model or the column level, but it is recommended that it be defined at the column level. Check constraints over multiple columns must be defined at the model level.
+dbt-databricks check constraints are defined only at the model level.
+
+```
+dbt-databricks
+
+models:
+  - name: my_model
+    meta:
+      constraints:
+        - name: id_greater_than_zero
+          condition: id > 0	
+    columns:
+      - name: name
+        meta:
+          constraint: not_null
+```
+
+```
+model contract
+
+models:
+  - name: my_model	
+    columns:
+      - name: name
+      data_type: integer
+      constraints: 
+        - type: not_null
+        - type: check
+          name: id_greater_than_zero
+          expression: "id > 0"
+```

tests/integration/persist_constraints/models/schema.yml

@@ -48,3 +48,15 @@ models:
         meta:
           constraint: not_null
       - name: date
+
+  - name: table_model_contract
+    config:
+      contract:
+        enforced: true
+    columns:
+      - name: id
+        data_type: int
+      - name: name
+        data_type: string
+      - name: date    
+        data_type: date    

tests/integration/persist_constraints/models/table_model_contract.sql

@@ -0,0 +1,3 @@
+{{config(materialized='table')}}
+
+select * from {{ ref('seed') }}

tests/integration/persist_constraints/test_persist_constraints.py

@@ -259,3 +259,28 @@ def test_databricks_sql_endpoint(self):
     @use_profile("databricks_uc_sql_endpoint")
     def test_databricks_uc_sql_endpoint(self):
         self.test_delta_constraints_disabled()
+
+
+class TestModelContractNotSupported(TestConstraints):
+    def test_model_contract_not_supported(self):
+        model_name = "table_model_contract"
+        self.run_dbt(["seed"])
+        self.run_and_check_failure(
+            model_name, err_msg="Model contracts are not currently supported."
+        )
+
+    @use_profile("databricks_cluster")
+    def test_databricks_cluster(self):
+        self.test_model_contract_not_supported()
+
+    @use_profile("databricks_uc_cluster")
+    def test_databricks_uc_cluster(self):
+        self.test_model_contract_not_supported()
+
+    @use_profile("databricks_sql_endpoint")
+    def test_databricks_sql_endpoint(self):
+        self.test_model_contract_not_supported()
+
+    @use_profile("databricks_uc_sql_endpoint")
+    def test_databricks_uc_sql_endpoint(self):
+        self.test_model_contract_not_supported()