Use `Schema.Builder#fromSchema` in SchemaUpdate

[wuchong]

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Description

Currently, SchemaUpdate maintains schema members (primary keys, columns, auto-incr fields), which is very error-prone, leading to missing schema members when we evolve the schema structure and resulting in a broken schema after schema evolution.

I suggest to directly maintain Schema.Builder in SchemaUpdate and delegating all schema changes to Schema.Builder. This help us to only maintain one logic of schema building and validation. 降低出问题的可能性。

Besides, the Schema.Builder#fromSchema should also be updated if needed.

Willingness to contribute

• I'm willing to submit a PR!

[Prajwal-banakar]

Hi @wuchong , I'm interested in working on this issue as a contributor. I understand the goal is to delegate schema changes to Schema.Builder. Are there any specific edge cases regarding primary keys or auto-increment fields I should be aware of before I start refactoring SchemaUpdate? If not, I'd love to take this on!

[wuchong]

Hi @Prajwal-banakar , I assigned this issue to you. I don't think there are any edge cases, but we may need some updates so the SchemaBuilder if existing API is not sufficient.

[Prajwal-banakar]

Hi @wuchong ,
I have refactored SchemaUpdate to directly maintain a Schema.Builder and delegate all schema changes to it, as suggested. I've also updated Schema.Builder#fromSchema and added a getColumn helper to the builder to ensure the API is sufficient for this delegation.

Ready for review!