alamb commented on issue #13753:
URL: https://github.com/apache/datafusion/issues/13753#issuecomment-2541366688
> I would said we made it public in datafusion-sql (or upstream to
sql-parser) but not moved to datafusion-common. I think we should eliminate
dependency to sql-parser in datafusion-common, we need to move those functions
or structs that have dependency to sql-parser out of datafusion-common to
datafusion-sql
I agree that making the builders / etc public in datafusion-sql is better
than dumping more stuff in datafusion-common
Another potential thought might be to move the unparsing code into its own
crate now given its non trivial complexity now. For example
`datafusion-unparser`
Another potential approach that would avoid adding a dependency on
`UserDefinedLogicalNode`(which is in `datafusion-expr`) on the unparser /
sqlparser might be:
1. Create a new `Unparseable` trait
2. Have the unparser try and downcast the `UserDefinedLogicalNode`
So something like
```rust
pub trait Unparseable {
/// User-defined nodes can override this method to provide a custom
/// implementation for the unparser.
fn unparse(
&self,
unparser: &Unparser,
query: &mut Option<QueryBuilder>,
select: &mut Option<SelectBuilder>,
relation: &mut Option<RelationBuilder>,
table_with_joins: &mut Option<TableWithJoinsBuilder>,
) -> Result<()> {
not_impl_err!("custom unparsing not implemented")
}
}
```
And then the unparser could do something like:
```rust
let user_defined_local_node: dyn &UserDefinedLogicalNode = ...;
// is the user defined node unparseable?
let Some(unparseable) = user_defined_local_node
.as_any()
.downcast_ref::<Unparseable>() else {
return plan_err!("Node type {} does not implement Unparseable",
user_defined_local_node.name())
}
let sql_nodes = unparseable.unparse(unparser, ....)
```
🤔
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