Add if_not_exists in OpWrite to make behavior more clear

[Xuanwo]

Discussed in #5223

^{Originally posted by Xuanwo October 22, 2024}
OpenDAL now supports the use of "*" in if_none_match to perform conditional write operations:

let _ = op.write_with(path, bs).if_none_match("*").await?;

However, it's somewhat difficult to grasp at first glance. Do you think it's a good idea to include if_not_exists?

So we can write code like:

let _ = op.write_with(path, bs).if_not_exists(true).await?;

---

After this change, we will still allow users to use if_none_match("*"), but we will no longer document it, making it a service implementation detail.

[kemingy]

Can I take this?

[Xuanwo]

Can I take this?

Of course. Thank you in advance, have fun!

[swanandx]

why are we passing a boolean to if_not_exists ? what will be behavior when we pass false?

let _ = op.write_with(path, bs).if_not_exists(false).await?;

[Xuanwo]

why are we passing a boolean to if_not_exists ?

Passing a boolean into if_not_exists make it easier to write code like:

async fn users_logic(require_not_exists: bool) {
  op.write_with(path, content).if_not_exists(require_not_exists).await;
}

Instead of:

async fn users_logic(require_not_exists: bool) {
  if require_not_exists {
    op.write_with(path, content).if_not_exists().await;
  } else {
    op.write_with(path, content).await;
  }
}

what will be behavior when we pass false?

This is a condition. While it's set to false, no such condition will be applied to this write operation.