Replace column index usage with attnums and Column model id

[silentninja]

Problem

Column index that is being used now is not robust and has few bugs related to its usage. For example db.constraints.operations.select.get_column_constraints will break if columns have been deleted, this comment explains the why attnums are robust identifiers

Proposed solution

PR #658 introduces the Column model which uses attnum, a robust alternate to column index. Hence column model id should be used at the service layer and attnum should be used in the place of column index at the data layer(db module)

We need to make at least the following changes:

• Column selecting operations should use attnum #992
• Column dropping operation should use attnum #993
• Column alteration operations should use attnum #994
• Column creation and copying should use attnum #995
• Remove column_index from MathesarColumn class #996
• Batch updating column using /tables/ api should reference column using id instead of column_index #1167

Additional context

• Blocked by:
  • Set up Column Django model with support for display options #658

[mathemancer]

I think the db layer identifier for the column should be the attnum, and the mathesar service layer should map between the column id used in the API and the attnum used by the database.

[kgodey]

Marking as ready since the prerequisite work has been merged.

[silentninja]

@kgodey Should these be part of the Initial data type milestone or improvements as the broken down issues seem to be part of improvements?

[kgodey]

@silentninja nice catch, I moved the broken down issues to Initial Data Types as well. I think it makes sense there since we're expanding the usage of columns through display options in that milestone.

[kgodey]

This is done.