Make it possible to force a column type and intricate bugfix.

columnar/src/column/mod.rs

@@ -35,7 +35,7 @@ impl<T: PartialOrd> Column<T> {
     }
 }
 
-impl<T: PartialOrd> Column<T> {
+impl<T: PartialOrd + Copy + Send + Sync + 'static> Column<T> {
     pub fn first(&self, row_id: RowId) -> Option<T> {
         self.values(row_id).next()
     }
@@ -44,6 +44,13 @@ impl<T: PartialOrd> Column<T> {
         self.value_row_ids(row_id)
             .map(|value_row_id: RowId| self.values.get_val(value_row_id))
     }
+
+    pub fn first_or_default_col(self, default_value: T) -> Arc<dyn ColumnValues<T>> {
+        Arc::new(FirstValueWithDefault {
+            column: self,
+            default_value,
+        })
+    }
 }
 
 impl<T> Deref for Column<T> {
@@ -65,3 +72,31 @@ impl BinarySerializable for Cardinality {
         Ok(cardinality)
     }
 }
+
+// TODO simplify or optimize
+struct FirstValueWithDefault<T: Copy> {
+    column: Column<T>,
+    default_value: T,
+}
+
+impl<T: PartialOrd + Send + Sync + Copy + 'static> ColumnValues<T> for FirstValueWithDefault<T> {
+    fn get_val(&self, idx: u32) -> T {
+        self.column.first(idx).unwrap_or(self.default_value)
+    }
+
+    fn min_value(&self) -> T {
+        self.column.values.min_value()
+    }
+
+    fn max_value(&self) -> T {
+        self.column.values.max_value()
+    }
+
+    fn num_vals(&self) -> u32 {
+        match &self.column.idx {
+            ColumnIndex::Full => self.column.values.num_vals(),
+            ColumnIndex::Optional(optional_idx) => optional_idx.num_rows(),
+            ColumnIndex::Multivalued(_) => todo!(),
+        }
+    }
+}

columnar/src/column_values/monotonic_mapping.rs

@@ -194,6 +194,20 @@ impl MonotonicallyMappableToU64 for i64 {
     }
 }
 
+impl MonotonicallyMappableToU64 for crate::DateTime {
+    #[inline(always)]
+    fn to_u64(self) -> u64 {
+        common::i64_to_u64(self.timestamp_micros)
+    }
+
+    #[inline(always)]
+    fn from_u64(val: u64) -> Self {
+        crate::DateTime {
+            timestamp_micros: common::u64_to_i64(val),
+        }
+    }
+}
+
 impl MonotonicallyMappableToU64 for bool {
     #[inline(always)]
     fn to_u64(self) -> u64 {

columnar/src/columnar/column_type.rs

@@ -1,3 +1,5 @@
+use std::net::Ipv6Addr;
+
 use crate::value::NumericalType;
 use crate::InvalidData;
 
@@ -11,10 +13,44 @@ pub enum ColumnType {
     I64 = 0u8,
     U64 = 1u8,
     F64 = 2u8,
-    Bytes = 3u8,
-    Str = 4u8,
-    Bool = 5u8,
-    IpAddr = 6u8,
+    Bytes = 10u8,
+    Str = 14u8,
+    Bool = 18u8,
+    IpAddr = 22u8,
+    DateTime = 26u8,
+}
+
+#[cfg(test)]
+const COLUMN_TYPES: [ColumnType; 8] = [
+    ColumnType::I64,
+    ColumnType::U64,
+    ColumnType::F64,
+    ColumnType::Bytes,
+    ColumnType::Str,
+    ColumnType::Bool,
+    ColumnType::IpAddr,
+    ColumnType::DateTime,
+];
+
+impl ColumnType {
+    pub fn to_code(self) -> u8 {
+        self as u8
+    }
+
+    pub(crate) fn try_from_code(code: u8) -> Result<ColumnType, InvalidData> {
+        use ColumnType::*;
+        match code {
+            0u8 => Ok(I64),
+            1u8 => Ok(U64),
+            2u8 => Ok(F64),
+            10u8 => Ok(Bytes),
+            14u8 => Ok(Str),
+            18u8 => Ok(Bool),
+            22u8 => Ok(IpAddr),
+            26u8 => Ok(Self::DateTime),
+            _ => Err(InvalidData),
+        }
+    }
 }
 
 impl From<NumericalType> for ColumnType {
@@ -33,26 +69,108 @@ impl ColumnType {
             ColumnType::I64 => Some(NumericalType::I64),
             ColumnType::U64 => Some(NumericalType::U64),
             ColumnType::F64 => Some(NumericalType::F64),
-            ColumnType::Bytes | ColumnType::Str | ColumnType::Bool | ColumnType::IpAddr => None,
+            ColumnType::Bytes
+            | ColumnType::Str
+            | ColumnType::Bool
+            | ColumnType::IpAddr
+            | ColumnType::DateTime => None,
         }
     }
+}
 
-    /// Encoded over 6 bits.
-    pub(crate) fn to_code(self) -> u8 {
-        self as u8
+// TODO remove if possible
+pub trait HasAssociatedColumnType: 'static + Send + Sync + Copy + PartialOrd {
+    fn column_type() -> ColumnType;
+    fn default_value() -> Self;
+}
+
+impl HasAssociatedColumnType for u64 {
+    fn column_type() -> ColumnType {
+        ColumnType::U64
     }
 
-    pub(crate) fn try_from_code(code: u8) -> Result<ColumnType, InvalidData> {
-        use ColumnType::*;
-        match code {
-            0u8 => Ok(I64),
-            1u8 => Ok(U64),
-            2u8 => Ok(F64),
-            3u8 => Ok(Bytes),
-            4u8 => Ok(Str),
-            5u8 => Ok(Bool),
-            6u8 => Ok(IpAddr),
-            _ => Err(InvalidData),
+    fn default_value() -> Self {
+        0u64
+    }
+}
+
+impl HasAssociatedColumnType for i64 {
+    fn column_type() -> ColumnType {
+        ColumnType::I64
+    }
+
+    fn default_value() -> Self {
+        0i64
+    }
+}
+
+impl HasAssociatedColumnType for f64 {
+    fn column_type() -> ColumnType {
+        ColumnType::F64
+    }
+
+    fn default_value() -> Self {
+        Default::default()
+    }
+}
+
+impl HasAssociatedColumnType for bool {
+    fn column_type() -> ColumnType {
+        ColumnType::Bool
+    }
+    fn default_value() -> Self {
+        Default::default()
+    }
+}
+
+impl HasAssociatedColumnType for crate::DateTime {
+    fn column_type() -> ColumnType {
+        ColumnType::DateTime
+    }
+    fn default_value() -> Self {
+        Default::default()
+    }
+}
+
+impl HasAssociatedColumnType for Ipv6Addr {
+    fn column_type() -> ColumnType {
+        ColumnType::IpAddr
+    }
+
+    fn default_value() -> Self {
+        Ipv6Addr::from([0u8; 16])
+    }
+}
+
+/// Column types are grouped into different categories that
+/// corresponds to the different types of `JsonValue` types.
+///
+/// The columnar writer will apply coercion rules to make sure that
+/// at most one column exist per `ColumnTypeCategory`.
+///
+/// See also [README.md].
+#[derive(Copy, Clone, Ord, PartialOrd, Eq, PartialEq, Debug)]
+#[repr(u8)]
+pub(crate) enum ColumnTypeCategory {
+    Bool,
+    Str,
+    Numerical,
+    DateTime,
+    Bytes,
+    IpAddr,
+}
+
+impl From<ColumnType> for ColumnTypeCategory {
+    fn from(column_type: ColumnType) -> Self {
+        match column_type {
+            ColumnType::I64 => ColumnTypeCategory::Numerical,
+            ColumnType::U64 => ColumnTypeCategory::Numerical,
+            ColumnType::F64 => ColumnTypeCategory::Numerical,
+            ColumnType::Bytes => ColumnTypeCategory::Bytes,
+            ColumnType::Str => ColumnTypeCategory::Str,
+            ColumnType::Bool => ColumnTypeCategory::Bool,
+            ColumnType::IpAddr => ColumnTypeCategory::IpAddr,
+            ColumnType::DateTime => ColumnTypeCategory::DateTime,
         }
     }
 }
@@ -73,7 +191,22 @@ mod tests {
                 assert!(column_type_set.insert(column_type));
             }
         }
-        assert_eq!(column_type_set.len(), 7);
+        assert_eq!(column_type_set.len(), super::COLUMN_TYPES.len());
+    }
+
+    #[test]
+    fn test_column_category_sort_consistent_with_column_type_sort() {
+        // This is a very important property because we
+        // we need to serialize colunmn in the right order.
+        let mut column_types: Vec<ColumnType> = super::COLUMN_TYPES.iter().copied().collect();
+        column_types.sort_by_key(|col| col.to_code());
+        let column_categories: Vec<ColumnTypeCategory> = column_types
+            .into_iter()
+            .map(ColumnTypeCategory::from)
+            .collect();
+        for (prev, next) in column_categories.iter().zip(column_categories.iter()) {
+            assert!(prev <= next);
+        }
     }
 
     #[test]

columnar/src/columnar/mod.rs

@@ -4,7 +4,7 @@ mod merge;
 mod reader;
 mod writer;
 
-pub use column_type::ColumnType;
+pub use column_type::{ColumnType, HasAssociatedColumnType};
 pub use merge::{merge_columnar, MergeDocOrder};
 pub use reader::ColumnarReader;
 pub use writer::ColumnarWriter;

columnar/src/columnar/reader/mod.rs

@@ -44,7 +44,7 @@ impl ColumnarReader {
         })
     }
 
-    // TODO fix ugly API
+    // TODO Add unit tests
     pub fn list_columns(&self) -> io::Result<Vec<(String, DynamicColumnHandle)>> {
         let mut stream = self.column_dictionary.stream()?;
         let mut results = Vec::new();
@@ -55,7 +55,8 @@ impl ColumnarReader {
                 .map_err(|_| io_invalid_data(format!("Unknown column code `{column_code}`")))?;
             let range = stream.value().clone();
             let column_name =
-                String::from_utf8_lossy(&key_bytes[..key_bytes.len() - 1]).to_string();
+                // The last two bytes are respectively the 0u8 separator and the column_type.
+                String::from_utf8_lossy(&key_bytes[..key_bytes.len() - 2]).to_string();
             let file_slice = self
                 .column_data
                 .slice(range.start as usize..range.end as usize);