Add table comments to SCHEMA_DATA.Models

[sanfrecce-osaka]

Motivation / Background

ActiveRecord allows comments on tables as well as columns.

cf. https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-table_comment

However, rails-mermaid_erd currently does not support table comments. I want comments on tables along with ER diagrams in the following cases.

• Discussion of model design
• Explanation to non-engineers
• Explanation to new team members during on-boarding

Detail

We can now output table comments to SCHEMA_DATA. We can get a table comment by using ::ActiveRecord::Base.connection.table_comment.

cf. https://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-table_comment

It was difficult to output them as ER diagram, so I implemented that they are output as mermaid code, it's similar to table names.