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new 4a41587bdf Make `custom_file_casts` example schema nullable to allow
null `id` values during casting (#20486)
4a41587bdf is described below
commit 4a41587bdfa43e9a012daa4405a1bdee43240623
Author: kosiew <[email protected]>
AuthorDate: Tue Feb 24 20:24:42 2026 +0800
Make `custom_file_casts` example schema nullable to allow null `id` values
during casting (#20486)
## Which issue does this PR close?
*
[Comment](https://github.com/apache/datafusion/pull/20202#discussion_r2804841561)
on #20202
---
## Rationale for this change
The `custom_file_casts` example defines a *logical/table* schema that
uses `id: Int32` as the target type. In practice, casting and projection
paths in DataFusion can produce **nulls** (e.g. failed casts, missing
values, or intermediate expressions), and examples should avoid implying
that nulls are impossible when demonstrating casting behavior.
Marking the `id` field as **nullable** makes the example more realistic
and prevents confusion when users follow or adapt the example to
scenarios where nulls may appear.
---
## What changes are included in this PR?
* Update the logical/table schema in `custom_file_casts.rs` to define
`id` as **nullable** (`Field::new("id", DataType::Int32, true)`).
* Adjust the inline comment to reflect the nullable schema.
---
## Are these changes tested?
No new tests were added.
This is a documentation/example-only change that updates a schema
definition and comment. The example continues to compile and can be
exercised by running the `custom_file_casts` example as before.
---
## Are there any user-facing changes?
Yes (example behavior/expectations):
* The `custom_file_casts` example now documents `id` as nullable,
aligning the example schema with situations where cast/projection may
yield null values.
* No public APIs are changed and no breaking behavior is introduced.
---
datafusion-examples/examples/custom_data_source/custom_file_casts.rs | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git
a/datafusion-examples/examples/custom_data_source/custom_file_casts.rs
b/datafusion-examples/examples/custom_data_source/custom_file_casts.rs
index 36cc936332..69826a59c9 100644
--- a/datafusion-examples/examples/custom_data_source/custom_file_casts.rs
+++ b/datafusion-examples/examples/custom_data_source/custom_file_casts.rs
@@ -49,9 +49,9 @@ use object_store::{ObjectStore, PutPayload};
pub async fn custom_file_casts() -> Result<()> {
println!("=== Creating example data ===");
- // Create a logical / table schema with an Int32 column
+ // Create a logical / table schema with an Int32 column (nullable)
let logical_schema =
- Arc::new(Schema::new(vec![Field::new("id", DataType::Int32, false)]));
+ Arc::new(Schema::new(vec![Field::new("id", DataType::Int32, true)]));
// Create some data that can be cast (Int16 -> Int32 is widening) and some
that cannot (Int64 -> Int32 is narrowing)
let store = Arc::new(InMemory::new()) as Arc<dyn ObjectStore>;
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