convert Postgres rows to arrow array

src/arrow_parquet.rs

@@ -1 +1,3 @@
+pub(crate) mod arrow_utils;
+pub(crate) mod pg_to_arrow;
 pub(crate) mod schema_visitor;

src/arrow_parquet/arrow_utils.rs

@@ -0,0 +1,47 @@
+use arrow::buffer::{NullBuffer, OffsetBuffer, ScalarBuffer};
+
+use crate::type_compat::map::CrunchyMap;
+
+pub(crate) fn arrow_map_offsets(maps: &Vec<Option<CrunchyMap>>) -> (OffsetBuffer<i32>, NullBuffer) {
+    let mut offsets = vec![0];
+    let mut nulls = vec![];
+
+    for map in maps {
+        if let Some(map) = map {
+            let len = map.entries.len() as i32;
+            offsets.push(offsets.last().expect("failed to get last map offset") + len);
+            nulls.push(true);
+        } else {
+            offsets.push(*offsets.last().expect("failed to get last map offset"));
+            nulls.push(false);
+        }
+    }
+
+    let offsets = OffsetBuffer::new(ScalarBuffer::from(offsets));
+    let nulls = NullBuffer::from(nulls);
+
+    (offsets, nulls)
+}
+
+pub(crate) fn arrow_array_offsets<T>(
+    pg_array: &Vec<Option<Vec<Option<T>>>>,
+) -> (OffsetBuffer<i32>, NullBuffer) {
+    let mut nulls = vec![];
+    let mut offsets = vec![0];
+
+    for pg_array in pg_array {
+        if let Some(pg_array) = pg_array {
+            let len = pg_array.len() as i32;
+            offsets.push(offsets.last().expect("failed to get last array offset") + len);
+            nulls.push(true);
+        } else {
+            offsets.push(*offsets.last().expect("failed to get last array offset"));
+            nulls.push(false);
+        }
+    }
+
+    let offsets = arrow::buffer::OffsetBuffer::new(arrow::buffer::ScalarBuffer::from(offsets));
+    let nulls = arrow::buffer::NullBuffer::from(nulls);
+
+    (offsets, nulls)
+}