Function generate_column_casts

src/sql/src/pure/postgres.rs:553–640

(
    scx: &StatementContext,
    table: &PostgresTableDesc,
    text_columns: &Vec<Ident>,
)

}

pub(crate) fn generate_column_casts(
    scx: &StatementContext,
    table: &PostgresTableDesc,
    text_columns: &Vec<Ident>,
) -> Result<Vec<(CastType, StorageScalarExpr)>, PlanError> {
    // Generate the cast expressions required to convert the text encoded columns into
    // the appropriate target types, creating a Vec<StorageScalarExpr>.
    // The postgres source reader will then eval each of those on the incoming rows.

    let text_columns = BTreeSet::from_iter(text_columns.iter().map(Ident::as_str));

    let mut table_cast = vec![];
    for (i, column) in table.columns.iter().enumerate() {
        let (cast_type, ty) = if text_columns.contains(column.name.as_str()) {
            // Treat the column as text if it was referenced in
            // `TEXT COLUMNS`. This is the only place we need to
            // perform this logic; even if the type is unsupported,
            // we'll be able to ingest its values as text in
            // storage.
            (CastType::Text, mz_pgrepr::Type::Text)
        } else {
            match mz_pgrepr::Type::from_oid_and_typmod(column.type_oid, column.type_mod) {
                Ok(t) => (CastType::Natural, t),
                // If this reference survived purification, we
                // do not expect it to be from a table that the
                // user will consume., i.e. expect this table to
                // be filtered out of table casts.
                Err(_) => {
                    table_cast.push((
                        CastType::Natural,
                        StorageScalarExpr::ErrorIfNull(
                            Box::new(StorageScalarExpr::Literal(
                                Row::pack_slice(&[Datum::Null]),
                                ReprColumnType {
                                    nullable: true,
                                    scalar_type: ReprScalarType::String,
                                },
                            )),
                            format!("Unsupported type with OID {}", column.type_oid),
                        ),
                    ));
                    continue;
                }
            }
        };

        let cast_expr = match pg_type_to_cast_func(scx, &ty) {
            Ok(None) => {
                // No cast needed (e.g. Text → String identity).
                StorageScalarExpr::Column(i)
            }
            Ok(Some(cast_func)) => {
                StorageScalarExpr::CallUnary(cast_func, Box::new(StorageScalarExpr::Column(i)))
            }
            Err(PlanError::TableContainsUningestableTypes { type_, .. }) => {
                // We expect only reg* types and similar to encounter
                // this. Users can ingest the data as text if they need
                // to. This is acceptable because we don't expect the