Method new

src/repr/src/row/encode.rs:1313–1348

Creates a [`RowColumnarDecoder`] that decodes from the provided [`StructArray`]. Returns an error if the schema of the [`StructArray`] does not match the provided [`RelationDesc`].

(col: StructArray, desc: &RelationDesc)

    /// Returns an error if the schema of the [`StructArray`] does not match
    /// the provided [`RelationDesc`].
    pub fn new(col: StructArray, desc: &RelationDesc) -> Result<Self, anyhow::Error> {
        let inner_columns = col.columns();
        let desc_columns = desc.typ().columns();

        if desc_columns.len() > inner_columns.len() {
            anyhow::bail!(
                "provided array has too few columns! {desc_columns:?} > {inner_columns:?}"
            );
        }

        // For performance reasons we downcast just a single time.
        let mut decoders = Vec::with_capacity(desc_columns.len());

        let null_mask = col.nulls();

        // The columns of the `StructArray` are named with their column index.
        for (col_idx, col_name, col_type) in desc.iter_all() {
            let field_name = col_idx.to_stable_name();
            let column = col.column_by_name(&field_name).ok_or_else(|| {
                anyhow::anyhow!(
                    "StructArray did not contain column name {field_name}, found {:?}",
                    col.column_names()
                )
            })?;
            let column = mask_nulls(column, null_mask);
            let null_count = col_type.nullable.then(|| column.null_count());
            let decoder = array_to_decoder(&column, &col_type.scalar_type)?;
            decoders.push((col_name.as_str().into(), null_count, decoder));
        }

        Ok(RowColumnarDecoder {
            len: col.len(),
            decoders,
            nullability: col.logical_nulls(),
        })
    }

    // Returns the number of null entries in this array of Row structs. This
    // will be 0 when `Row` is encoded directly, but could be non-zero when it's