SchemaMeta

typed_arrow::schema

Trait SchemaMeta 

Source 
pub trait SchemaMeta: Record {
    // Required method
    fn fields() -> Vec<Field>;

    // Provided methods
    fn metadata() -> HashMap<String, String> { ... }
    fn schema() -> Arc<Schema> { ... }
}
Expand description

Arrow runtime schema metadata for a top-level Record.

Required Methods§

Source

fn fields() -> Vec<Field>

Top-level fields: (name, data_type, nullable) represented as Fields.

Provided Methods§

Source

fn metadata() -> HashMap<String, String>

Optional top-level schema key/value metadata.

Source

fn schema() -> Arc<Schema>

Construct an Arc<arrow_schema::Schema> from fields().

Examples found in repository?
examples/08_record_batch.rs (line 45)
19fn main() {
20    let rows = vec![
21        PersonRB {
22            id: 1,
23            address: Some(AddressRB {
24                city: "NYC".into(),
25                zip: None,
26            }),
27            email: Some("a@example.com".into()),
28        },
29        PersonRB {
30            id: 2,
31            address: None,
32            email: None,
33        },
34        PersonRB {
35            id: 3,
36            address: Some(AddressRB {
37                city: "SF".into(),
38                zip: Some(94111),
39            }),
40            email: Some("c@example.com".into()),
41        },
42    ];
43
44    // Schema from type
45    let schema = <PersonRB as SchemaMeta>::schema();
46    println!("fields={}", schema.fields().len());
47
48    // Build arrays from rows and into RecordBatch
49    let mut b = <PersonRB as BuildRows>::new_builders(rows.len());
50    b.append_rows(rows);
51    let arrays = b.finish();
52    let batch: RecordBatch = arrays.into_record_batch();
53    println!(
54        "batch_rows={}, field0={}, field1={}, field2={}",
55        batch.num_rows(),
56        batch.schema().field(0).name(),
57        batch.schema().field(1).name(),
58        batch.schema().field(2).name()
59    );
60
61    // A quick peek at nested values
62    let city = as_string_array(arrow_array::cast::as_struct_array(batch.column(1)).column(0));
63    println!("first_city={}, third_city={}", city.value(0), city.value(2));
64}

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors§