marvinlanhenke commented on issue #264:
URL: https://github.com/apache/iceberg-rust/issues/264#issuecomment-1997524951
@liurenjie1024
...just to make sure I'm on the right track - and to confirm the idea.
Here is what I would (high-level):
- implement `fn project` on Transform
- match Transform & orginal BoundPredicate
- handle each Transform (e.g. Bucket) and Predicate according to Java
Implementation
- return `Option<Predicate>`
In order to implement the `ProjectionEvaluator` later, we can then get the
`PartitionSpec` from the manifest, iterate over `fields: Vec<PartitionField>`
and call `fn project(...)` on each field's transform...
some pseudo-implementation to illustrate:
```rust
impl Transform {
// ...
pub fn project(&self, name: String, pred: &BoundPredicate) ->
Option<Predicate> {
match self {
Transform::Bucket(_) => match pred {
BoundPredicate::Unary(expr) =>
Some(Predicate::Unary(UnaryExpression::new(
expr.op(),
Reference::new(name),
))),
_ => unimplemented!(),
},
_ => unimplemented!(),
}
}
}
```
```rust
#[test]
fn test_bucket_project() {
let trans = Transform::Bucket(8);
let name = "projected_name".to_string();
let field = NestedField::required(1, "a",
Type::Primitive(PrimitiveType::Int));
let pred = BoundPredicate::Unary(UnaryExpression::new(
PredicateOperator::IsNull,
BoundReference::new("original_name", Arc::new(field)),
));
let result = trans.project(name, &pred).unwrap();
assert_eq!(format!("{result}"), "projected_name IS NULL");
}
```
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