Re: [PR] Add support for `Dictionary` to AST datatype in unparser [datafusion]

[via GitHub]

phillipleblanc commented on code in PR #14783:
URL: https://github.com/apache/datafusion/pull/14783#discussion_r1967078010


##########
datafusion/sql/src/unparser/expr.rs:
##########
@@ -1624,9 +1624,7 @@ impl Unparser<'_> {
             DataType::Union(_, _) => {
                 not_impl_err!("Unsupported DataType: conversion: 
{data_type:?}")
             }
-            DataType::Dictionary(_, _) => {
-                not_impl_err!("Unsupported DataType: conversion: 
{data_type:?}")
-            }
+            DataType::Dictionary(_, val) => self.arrow_dtype_to_ast_dtype(val),

Review Comment:
   Let's add a test for this new type, see this example for supporting the 
Utf8View type:
   
   ```rust
       #[test]
       fn test_utf8_view_to_sql() -> Result<()> {
           let dialect = CustomDialectBuilder::new()
               .with_utf8_cast_dtype(ast::DataType::Char(None))
               .build();
           let unparser = Unparser::new(&dialect);
   
           let ast_dtype = 
unparser.arrow_dtype_to_ast_dtype(&DataType::Utf8View)?;
   
           assert_eq!(ast_dtype, ast::DataType::Char(None));
   
           let expr = cast(col("a"), DataType::Utf8View);
           let ast = unparser.expr_to_sql(&expr)?;
   
           let actual = format!("{}", ast);
           let expected = r#"CAST(a AS CHAR)"#.to_string();
   
           assert_eq!(actual, expected);
   
           let expr = 
col("a").eq(lit(ScalarValue::Utf8View(Some("hello".to_string()))));
           let ast = unparser.expr_to_sql(&expr)?;
   
           let actual = format!("{}", ast);
           let expected = r#"(a = 'hello')"#.to_string();
   
           assert_eq!(actual, expected);
   
           let expr = col("a").is_not_null();
   
           let ast = unparser.expr_to_sql(&expr)?;
           let actual = format!("{}", ast);
           let expected = r#"a IS NOT NULL"#.to_string();
   
           assert_eq!(actual, expected);
   
           let expr = col("a").is_null();
   
           let ast = unparser.expr_to_sql(&expr)?;
           let actual = format!("{}", ast);
           let expected = r#"a IS NULL"#.to_string();
   
           assert_eq!(actual, expected);
   
           Ok(())
       }
   ```



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