cj-zhukov commented on code in PR #18862:
URL: https://github.com/apache/datafusion/pull/18862#discussion_r2552263952
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datafusion-examples/examples/dataframe/default_column_values.rs:
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@@ -52,25 +54,23 @@ use object_store::{ObjectStore, PutPayload};
// Metadata key for storing default values in field metadata
const DEFAULT_VALUE_METADATA_KEY: &str = "example.default_value";
-// Example showing how to implement custom default value handling for missing
columns
-// using field metadata and PhysicalExprAdapter.
-//
-// This example demonstrates how to:
-// 1. Store default values in field metadata using a constant key
-// 2. Create a custom PhysicalExprAdapter that reads these defaults
-// 3. Inject default values for missing columns in filter predicates
-// 4. Use the DefaultPhysicalExprAdapter as a fallback for standard schema
adaptation
-// 5. Wrap string default values in cast expressions for proper type conversion
-//
-// Important: PhysicalExprAdapter is specifically designed for rewriting
filter predicates
-// that get pushed down to file scans. For handling missing columns in
projections,
-// other mechanisms in DataFusion are used (like SchemaAdapter).
-//
-// The metadata-based approach provides a flexible way to store default values
as strings
-// and cast them to the appropriate types at query time.
-
-#[tokio::main]
-async fn main() -> Result<()> {
+/// Example showing how to implement custom default value handling for missing
columns
+/// using field metadata and PhysicalExprAdapter.
+///
+/// This example demonstrates how to:
+/// 1. Store default values in field metadata using a constant key
+/// 2. Create a custom PhysicalExprAdapter that reads these defaults
+/// 3. Inject default values for missing columns in filter predicates
+/// 4. Use the DefaultPhysicalExprAdapter as a fallback for standard schema
adaptation
+/// 5. Wrap string default values in cast expressions for proper type
conversion
+///
+/// Important: PhysicalExprAdapter is specifically designed for rewriting
filter predicates
+/// that get pushed down to file scans. For handling missing columns in
projections,
+/// other mechanisms in DataFusion are used (like SchemaAdapter).
+///
+/// The metadata-based approach provides a flexible way to store default
values as strings
+/// and cast them to the appropriate types at query time.
+pub async fn default_column_values() -> Result<()> {
Review Comment:
Agree with you, let's move the example
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