kosiew
4a41587bdf
## 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.
Apache DataFusion
DataFusion is an extensible query engine written in Rust that uses Apache Arrow as its in-memory format.
This crate provides libraries and binaries for developers building fast and feature-rich database and analytic systems, customized for particular workloads. See use cases for examples. The following related subprojects target end users:
- DataFusion Python offers a Python interface for SQL and DataFrame queries.
- DataFusion Comet is an accelerator for Apache Spark based on DataFusion.
"Out of the box," DataFusion offers SQL and DataFrame APIs, excellent performance, built-in support for CSV, Parquet, JSON, and Avro, extensive customization, and a great community.
DataFusion features a full query planner, a columnar, streaming, multi-threaded, vectorized execution engine, and partitioned data sources. You can customize DataFusion at almost all points including additional data sources, query languages, functions, custom operators and more. See the Architecture section for more details.
Here are links to important resources:
- Project Site
- Installation
- Rust Getting Started
- Rust DataFrame API
- Rust API docs
- Rust Examples
- Python DataFrame API
- Architecture
What can you do with this crate?
DataFusion is great for building projects such as domain-specific query engines, new database platforms and data pipelines, query languages and more. It lets you start quickly from a fully working engine, and then customize those features specific to your needs. See the list of known users.
Contributing to DataFusion
Please see the contributor guide and communication pages for more information.
Crate features
This crate has several features which can be specified in your Cargo.toml.
Default features:
nested_expressions: functions for working with nested types such asarray_to_stringcompression: reading files compressed withxz2,bzip2,flate2, andzstdcrypto_expressions: cryptographic functions such asmd5andsha256datetime_expressions: date and time functions such asto_timestampencoding_expressions:encodeanddecodefunctionsparquet: support for reading the Apache Parquet formatsql: support for SQL parsing and planningregex_expressions: regular expression functions, such asregexp_matchunicode_expressions: include Unicode-aware functions such ascharacter_lengthunparser: enables support to reverse LogicalPlans back into SQLrecursive_protection: uses recursive for stack overflow protection.
Optional features:
avro: support for reading the Apache Avro formatbacktrace: include backtrace information in error messagesparquet_encryption: support for using Parquet Modular Encryptionserde: enable arrow-schema'sserdefeature
DataFusion API Evolution and Deprecation Guidelines
Public methods in Apache DataFusion evolve over time: while we try to maintain a stable API, we also improve the API over time. As a result, we typically deprecate methods before removing them, according to the deprecation guidelines.
Dependencies and Cargo.lock
Following the guidance on committing Cargo.lock files, this project commits
its Cargo.lock file.
CI uses the committed Cargo.lock file, and dependencies are updated regularly
using Dependabot PRs.