New functionality - Retrieve the description for identical column names from upstream models

[b-per]

This is a:

• bug fix PR with no breaking changes — please ensure the base branch is main
• new functionality — please ensure the base branch is the latest dev/ branch
• a breaking change — please ensure the base branch is the latest dev/ branch

Description & motivation

When using the macro generate_model_yaml it can be cumbersome to have to copy/paste the description of the columns from the upstream models, especially when many models are joined together.

The new feature accessible via the flag upstream_descriptions=True (defaulted to False) parses the Jinja graph to retrieve existing descriptions in parent models.

An example of output is the following, when the upstream model has an existing description of description column a:

I am not too sure where I should add the entry in CHANGELOG.md

Checklist

• I have verified that these changes work locally
• I have updated the README.md (if applicable)
• I have added tests & descriptions to my models (and macros if applicable)
• I have added an entry to CHANGELOG.md

[dbeatty10]

Thanks for this awesome enhancement, @b-per! 💪

Integration test and readme looks great.

Two things for you to do:

1. I left feedback on two very small things
2. Example for adding CHANGELOG entry below

Changlog entry

I am not too sure where I should add the entry in CHANGELOG.md

You can follow this pattern for adding to the changelog. Something like this:

# Unreleased
## New features
- Awesome description of fabulous new feature here ([#61](https://github.com/dbt-labs/dbt-utils/pull/61)) 

[dbeatty10]

Looking good!

Could you take a look at the build in CircleCI? Looks like test_generate_model_yaml_upstream_descriptions isn't passing.

Accidentally overlooked CircleCI failure originally

[b-per]

I got quite puzzled about why the test was passing locally but not in CI, before I realized that I needed to add a dbt run to the CI step to get codegen to list the column of the downstream model.

It should be all-good now!

[dbeatty10]

Nice catch, @b-per

👍 Everything looks good.