Support Delta constraints (#71)

### Description
This PR adds support for [Delta Constraints](https://docs.databricks.com/delta/delta-constraints.html) with dbt table models and incremental models. It supports two types of constraints: model level [Check constraint](https://docs.databricks.com/delta/delta-constraints.html#check-constraint) and column level [not_null](https://docs.databricks.com/delta/delta-constraints.html#not-null-constraint) constraint. 

Users can specify model-level and column-level constraints under the `meta` field of the model config. For example:
```yaml
# schema.yml
models:
  - name: my_model
    meta:
      constraints:
        - name: id_greater_than_zero
          condition: id > 0	
    columns:
      - name: id
      - name: name
        meta:
          constraint: not_null
```
Constraints specified will be created if the `persist_constraints` config is enabled (default: false):
```sql
-- my_model.sql
{{ config(
    materailized='table',
    persist_constraints=True
) }}
...
```

Note, Delta constraints are only available in Databricks Runtime 7.4 and above. So DBR 7.3 LTS won't support this feature.

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## dbt-databricks 1.1.0 (Release TBD)
 
+### Features
+- Add support for [Delta constraints](https://docs.databricks.com/delta/delta-constraints.html) ([#71](https://github.com/databricks/dbt-databricks/pull/71))
+
 ### Under the hood
 - Port testing framework changes from [dbt-labs/dbt-spark#299](https://github.com/dbt-labs/dbt-spark/pull/299) and [dbt-labs/dbt-spark#314](https://github.com/dbt-labs/dbt-spark/pull/314) ([#70](https://github.com/databricks/dbt-databricks/pull/70))
 

README.md

@@ -51,5 +51,5 @@ your_profile_name:
 
 ### Compatibility
 
-The `dbt-databricks` adapter has been tested against `Databricks SQL` and `Databricks runtime releases 7.3 LTS` and later.
+The `dbt-databricks` adapter has been tested against `Databricks SQL` and `Databricks runtime releases 9.1 LTS` and later.
 

dbt/include/databricks/macros/adapters.sql

@@ -87,3 +87,59 @@
     {% endfor %}
   {% endif %}
 {% endmacro %}
+
+{# Persist table-level and column-level constraints. #}
+{% macro persist_constraints(relation, model) %}
+  {{ return(adapter.dispatch('persist_constraints', 'dbt')(relation, model)) }}
+{% endmacro %}
+
+{% macro databricks__persist_constraints(relation, model) %}
+  {% 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) %}
+  {% endif %}
+{% endmacro %}
+
+{% macro alter_table_add_constraints(relation, constraints) %}
+  {{ return(adapter.dispatch('alter_table_add_constraints', 'dbt')(relation, constraints)) }}
+{% endmacro %}
+
+{% macro databricks__alter_table_add_constraints(relation, constraints) %}
+  {% if constraints is sequence %}
+    {% for constraint in constraints %}
+      {% set name = constraint['name'] %}
+      {% if not name %}
+        {{ exceptions.raise_compiler_error('Invalid check constraint name: ' ~ name) }}
+      {% endif %}
+      {% set condition = constraint['condition'] %}
+      {% if not condition %}
+        {{ exceptions.raise_compiler_error('Invalid check constraint condition: ' ~ condition) }}
+      {% endif %}
+      {# Skip if the update is incremental. #}
+      {% if not is_incremental() %}
+        {% call statement() %}
+          alter table {{ relation }} add constraint {{ name }} check ({{ condition }});
+        {% endcall %}
+      {% endif %}
+    {% endfor %}
+  {% endif %}
+{% endmacro %}
+
+{% macro alter_column_set_constraints(relation, column_dict) %}
+  {{ return(adapter.dispatch('alter_column_set_constraints', 'dbt')(relation, column_dict)) }}
+{% endmacro %}
+
+{% macro databricks__alter_column_set_constraints(relation, column_dict) %}
+  {% for column_name in column_dict %}
+    {% set constraint = column_dict[column_name]['meta']['constraint'] %}
+    {% if constraint %}
+      {% if constraint != 'not_null' %}
+        {{ exceptions.raise_compiler_error('Invalid constraint for column ' ~ column_name ~ '. Only `not_null` is supported.') }}
+      {% endif %}
+      {% set quoted_name = adapter.quote(column_name) if column_dict[column_name]['quote'] else column_name %}
+      {% call statement() %}
+        alter table {{ relation }} change column {{ quoted_name }} set not null
+      {% endcall %}
+    {% endif %}
+  {% endfor %}
+{% endmacro %}

dbt/include/databricks/macros/materializations/incremental/incremental.sql

@@ -43,6 +43,8 @@
 
   {% do persist_docs(target_relation, model) %}
 
+  {% do persist_constraints(target_relation, model) %}
+
   {{ run_hooks(post_hooks) }}
 
   {{ return({'relations': [target_relation]}) }}

dbt/include/databricks/macros/materializations/snapshot.sql

@@ -96,6 +96,8 @@
 
   {% do persist_docs(target_relation, model) %}
 
+  {% do persist_constraints(target_relation, model) %}
+
   {{ run_hooks(post_hooks, inside_transaction=True) }}
 
   {{ adapter.commit() }}

dbt/include/databricks/macros/materializations/table.sql

@@ -24,6 +24,8 @@
 
   {% do persist_docs(target_relation, model) %}
 
+  {% do persist_constraints(target_relation, model) %}
+
   {{ run_hooks(post_hooks) }}
 
   {{ return({'relations': [target_relation]})}}

tests/integration/persist_constraints/insert_invalid_id.sql

@@ -0,0 +1 @@
+insert into {schema}.seed values (0, 'Cathy', '2022-03-01');

tests/integration/persist_constraints/insert_invalid_name.sql

@@ -0,0 +1 @@
+insert into {schema}.seed values (3, null, '2022-03-01');

tests/integration/persist_constraints/models/expected/expected_incremental_model.sql

@@ -0,0 +1,7 @@
+{{ config(materialized='table') }}
+
+select * from values
+  (1, 'Alice', '2022-01-01'),
+  (2, 'Bob', '2022-02-01'),
+  (3, 'Cathy', '2022-03-01')
+t(id, name, date);

tests/integration/persist_constraints/models/expected/expected_model.sql

@@ -0,0 +1,6 @@
+{{ config(materialized='table') }}
+
+select * from values
+  (1, 'Alice', '2022-01-01'),
+  (2, 'Bob', '2022-02-01')
+t(id, name, date);

tests/integration/persist_constraints/models/expected/expected_model_with_invalid_name.sql

@@ -0,0 +1,7 @@
+{{ config(materialized='table') }}
+
+select * from values
+  (1, 'Alice', '2022-01-01'),
+  (2, 'Bob', '2022-02-01'),
+  (3, null, '2022-03-01')
+t(id, name, date);

tests/integration/persist_constraints/models/incremental_model.sql

@@ -0,0 +1,7 @@
+{{config(materialized='incremental')}}
+
+select * from {{ ref('seed') }}
+
+{% if is_incremental() %}
+  where date > (select max(date) from {{ this }})
+{% endif %}

tests/integration/persist_constraints/models/invalid_check_constraint.sql

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

tests/integration/persist_constraints/models/invalid_column_constraint.sql

@@ -0,0 +1,4 @@
+{{config(materialized='table')}}
+
+select * from {{ ref('seed') }}
+

tests/integration/persist_constraints/models/schema.yml

@@ -0,0 +1,50 @@
+version: 2
+
+models:
+  - name: table_model
+    meta:
+      constraints:
+        - name: id_greater_than_zero
+          condition: id > 0
+    columns:
+      - name: id
+      - name: name
+        meta:
+          constraint: not_null
+      - name: date
+
+  - name: incremental_model
+    meta:
+      constraints:
+        - name: id_greater_than_zero
+          condition: id > 0
+    columns:
+      - name: id
+      - name: name
+        meta:
+          constraint: not_null
+      - name: date
+
+  - name: invalid_check_constraint
+    meta:
+      constraints:
+        - name: invalid_constraint
+          condition:
+
+  - name: invalid_column_constraint
+    columns:
+      - name: id
+        meta:
+          constraint: invalid
+
+  - name: table_model_disable_constraints
+    meta:
+      constraints:
+        - name: id_greater_than_zero
+          condition: id > 0
+    columns:
+      - name: id
+      - name: name
+        meta:
+          constraint: not_null
+      - name: date

tests/integration/persist_constraints/models/table_model.sql

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

tests/integration/persist_constraints/models/table_model_disable_constraints.sql

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

tests/integration/persist_constraints/seeds/seed.csv

@@ -0,0 +1,3 @@
+id,name,date
+1,Alice,2022-01-01
+2,Bob,2022-02-01

tests/integration/persist_constraints/seeds/seed.yml

@@ -0,0 +1,9 @@
+version: 2
+
+seeds:
+  - name: seed
+    config:
+      column_types:
+        id: int
+        name: string
+        date: string

tests/integration/persist_constraints/snapshots/snapshot.sql

@@ -0,0 +1,15 @@
+{% snapshot my_snapshot %}
+
+    {{
+        config(
+          check_cols=["name", "date"],
+          unique_key="id",
+          strategy="check",
+          target_schema=schema
+        )
+
+    }}
+
+    select * from {{ ref('seed') }}
+
+{% endsnapshot %}

tests/integration/persist_constraints/snapshots/snapshot.yml

@@ -0,0 +1,12 @@
+version: 2
+
+snapshots:
+  - name: my_snapshot
+    meta:
+      constraints:
+        - name: id_greater_than_zero
+          condition: id > 0
+    columns:
+      - name: name
+        meta:
+          constraint: not_null