alamb commented on code in PR #13063:
URL: https://github.com/apache/datafusion/pull/13063#discussion_r1811275590
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datafusion/core/src/datasource/schema_adapter.rs:
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@@ -99,8 +107,86 @@ pub trait SchemaMapper: Debug + Send + Sync {
) -> datafusion_common::Result<RecordBatch>;
}
-/// Implementation of [`SchemaAdapterFactory`] that maps columns by name
-/// and casts columns to the expected type.
+/// Default [`SchemaAdapterFactory`] for mapping schemas.
+///
+/// This can be used to adapt file-level record batches to a table schema and
+/// implement schema evolution.
+///
+/// Given an input file schema and a table schema, this factor can make
+/// [`SchemaMapper`]s that:
+///
+/// 1. Reorder columns
+/// 2. Cast columns to the correct type
+/// 3. Fill missing columns with nulls
Review Comment:
It errors -- I will add a test / improve the docs
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