Documentation Index
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DuckDB LIST and MAP scalar functions as typed Diesel DSL: array_length/len, list_reverse/sort/distinct/concat, array_to_string, and cardinality/map_keys/map_values.
LIST and MAP types, exposed as free functions in
better_duck_diesel::dsl::*. List arguments and results are typed DuckList; map arguments are typed
DuckMap.
use diesel::prelude::*;
use better_duck_diesel::dsl::*;
| Function | Signature | Returns |
|---|---|---|
array_length(list) | DuckList | BigInt |
len(list) | DuckList | BigInt |
list_reverse(list) | DuckList | DuckList |
list_sort(list) | DuckList | DuckList |
list_distinct(list) | DuckList | DuckList |
list_concat(a, b) | DuckList, DuckList | DuckList |
array_to_string(list, sep) | DuckList, Text | Text |
let joined: Vec<String> = readings::table
.select(array_to_string(readings::tags, ","))
.load(&mut conn)?;
| Function | Signature | Returns |
|---|---|---|
cardinality(map) | DuckMap | DuckUBigInt |
map_keys(map) | DuckMap | DuckList |
map_values(map) | DuckMap | DuckList |
DuckList (or DuckUBigInt) cannot be loaded through the typed
select builder — the Duck* SQL types have no Queryable blanket impl. To read such a result, route the
query through diesel::sql_query(...) with a QueryableByName struct whose field carries
#[diesel(sql_type = DuckList)]. Functions that reduce a list to a standard type — array_length,
len, array_to_string — load normally. See
Type mapping.DuckList / DuckMap and how to read them.array_agg builds a DuckList.