model contracts + constraints with nested fields

[MichelleArk]

resolves #673

Description

🎩

-- nested_fields.yml
version: 2

models:
  - name: double_nested_fields
    config:
      contract: {enforced: true}
      materialized: table
    columns:
      - name: a
        data_type: string
      - name: b.id
        data_type: integer
        constraints:
          - type: not_null
      - name: b.name
        description: test description
        data_type: string
      - name: b.double_nested.id
        data_type: integer
      - name: b.double_nested.another.again
        data_type: string
      - name: b.double_nested.another.even_more
        data_type: integer
        constraints: 
          - type: not_null

-- double_nested_fields.sql
select
  'string' as a,
  struct(
    1 as id,
    'name' as name,
    struct(2 as id, struct('test' as again, '2' as even_more) as another) as double_nested
  ) as b

❯ dbt run --select double_nested_fields --project-dir ~/basic-dbt
...
21:31:07  
21:31:07  Compilation Error in model double_nested_fields (models/double_nested_fields.sql)
21:31:07    This model has an enforced contract that failed.
21:31:07    Please ensure the name, data_type, and number of columns in your contract match the columns in your model's definition.
21:31:07    
21:31:07    | column_name                       | definition_type | contract_type | mismatch_reason    |
21:31:07    | --------------------------------- | --------------- | ------------- | ------------------ |
21:31:07    | b.double_nested.another.even_more | STRING          | INT64         | data type mismatch |

Fixing the incorrect data type, dbt run passes ✅

Checklist

• I have read the contributing guide and understand what's expected of me
• I have signed the CLA
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have opened an issue to add/update docs, or docs changes are not required/relevant for this PR: Add example of colum-level constraint on a nested column in BigQuery docs.getdbt.com#3454
• I have run changie new to create a changelog entry

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-bigquery contributing guide.

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the dbt-bigquery contributing guide.

[MichelleArk]

Opened a follow-up tech debt issue to adopt this convention + implementation in dbt-core at some point in the future: dbt-labs/dbt-core#7759. Presently, BigQuery's support of nested columns + constraints is most maturely supported and keeping the implementation focused on BigQuery will prevent a large scope increase of this issue.

[gshank]

Code itself looks fine (though I'm not completely familiar). There's a failing functional test which might be related though.

[MichelleArk]

The failing integration test looks related to some recently merged changes for fixes to foreign key rendering that made the base test a little less generic than it previously was. I have a fix in another PR related to constraints but will move it out into its own PR to unblock this work.

[github-actions]

The backport to 1.5.latest failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-1.5.latest 1.5.latest
# Navigate to the new working tree
cd .worktrees/backport-1.5.latest
# Create a new branch
git switch --create backport-738-to-1.5.latest
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 b1e950bf6f8f6c3528b65080e257b746839ef87c
# Push it to GitHub
git push --set-upstream origin backport-738-to-1.5.latest
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.5.latest

Then, create a pull request where the base branch is 1.5.latest and the compare/head branch is backport-738-to-1.5.latest.