Variant data type support

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 <!-- next-header -->
 
 ## [Unreleased] - ReleaseDate
+### Added
+- [Variant data type](https://clickhouse.com/docs/en/sql-reference/data-types/variant) support ([#170]).
+
+[#170]: https://github.com/ClickHouse/clickhouse-rs/pull/170
 
 ## [0.13.1] - 2024-10-21
 ### Added

Cargo.toml

@@ -49,6 +49,10 @@ required-features = ["rustls-tls"]
 name = "data_types_derive_simple"
 required-features = ["time", "uuid"]
 
+[[example]]
+name = "data_types_variant"
+required-features = ["time"]
+
 [profile.release]
 debug = true
 

README.md

@@ -438,13 +438,36 @@ How to choose between all these features? Here are some considerations:
     }
     ```
     </details>
+* `Variant` data type is supported as a Rust enum. As the inner Variant types are _always_ sorted alphabetically, Rust enum variants should be defined in the _exactly_ same order as it is in the data type; their names are irrelevant, only the order of the types matters. This following example has a column defined as `Variant(Array(UInt16), Bool, Date, String, UInt32)`:
+    <details>
+    <summary>Example</summary>
+
+    ```rust,ignore
+    #[derive(Serialize, Deserialize)]
+    enum MyRowVariant {
+        Array(Vec<i16>),
+        Boolean(bool),
+        #[serde(with = "clickhouse::serde::time::date")]
+        Date(time::Date),
+        String(String),
+        UInt32(u32),
+    }
+
+    #[derive(Row, Serialize, Deserialize)]
+    struct MyRow {
+        id: u64,
+        var: MyRowVariant,
+    }
+    ```
+    </details>
 * [New `JSON` data type](https://clickhouse.com/docs/en/sql-reference/data-types/newjson) is currently supported as a string when using ClickHouse 24.10+. See [this example](examples/data_types_new_json.rs) for more details.
-* `Variant`, `Dynamic` types are not supported for now.
+* `Dynamic` data type is not supported for now.
 
 See also the additional examples:
 
 * [Simpler ClickHouse data types](examples/data_types_derive_simple.rs)
 * [Container-like ClickHouse data types](examples/data_types_derive_containers.rs)
+* [Variant data type](examples/data_types_variant.rs)
 
 ## Mocking
 The crate provides utils for mocking CH server and testing DDL, `SELECT`, `INSERT` and `WATCH` queries.

examples/README.md

@@ -18,6 +18,7 @@ If something is missing, or you found a mistake in one of these examples, please
 
 - [data_types_derive_simple.rs](data_types_derive_simple.rs) - deriving simpler ClickHouse data types in a struct. Required cargo features: `time`, `uuid`.
 - [data_types_derive_containers.rs](data_types_derive_containers.rs) - deriving container-like (Array, Tuple, Map, Nested, Geo) ClickHouse data types in a struct.
+- [data_types_variant.rs](data_types_variant.rs) - working with the [Variant data type](https://clickhouse.com/docs/en/sql-reference/data-types/variant).
 - [data_types_new_json.rs](data_types_new_json.rs) - working with the [new JSON data type](https://clickhouse.com/docs/en/sql-reference/data-types/newjson) as a String.
 
 ### Special cases

examples/data_types_variant.rs

@@ -0,0 +1,169 @@
+use clickhouse_derive::Row;
+use serde::{Deserialize, Serialize};
+
+use clickhouse::sql::Identifier;
+use clickhouse::{error::Result, Client};
+
+// See also: https://clickhouse.com/docs/en/sql-reference/data-types/variant
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    let table_name = "chrs_data_types_variant";
+    let client = Client::default().with_url("http://localhost:8123");
+
+    // No matter the order of the definition on the Variant types in the DDL, this particular Variant will always be sorted as follows:
+    // Variant(Array(UInt16), Bool, FixedString(6), Float32, Float64, Int128, Int16, Int32, Int64, Int8, String, UInt128, UInt16, UInt32, UInt64, UInt8)
+    client
+        .query(
+            "
+            CREATE OR REPLACE TABLE ?
+            (
+                `id`  UInt64,
+                `var` Variant(
+                          Array(UInt16),
+                          Bool,
+                          Date,
+                          FixedString(6),
+                          Float32, Float64,
+                          Int128, Int16, Int32, Int64, Int8,
+                          String,
+                          UInt128, UInt16, UInt32, UInt64, UInt8
+                      )
+            )
+            ENGINE = MergeTree
+            ORDER BY id",
+        )
+        .bind(Identifier(table_name))
+        .with_option("allow_experimental_variant_type", "1")
+        // This is required only if we are mixing similar types in the Variant definition
+        // In this case, this is various Int/UInt types, Float32/Float64, and String/FixedString
+        // Omit this option if there are no similar types in the definition
+        .with_option("allow_suspicious_variant_types", "1")
+        .execute()
+        .await?;
+
+    let mut insert = client.insert(table_name)?;
+    let rows_to_insert = get_rows();
+    for row in rows_to_insert {
+        insert.write(&row).await?;
+    }
+    insert.end().await?;
+
+    let rows = client
+        .query("SELECT ?fields FROM ?")
+        .bind(Identifier(table_name))
+        .fetch_all::<MyRow>()
+        .await?;
+
+    println!("{rows:#?}");
+    Ok(())
+}
+
+fn get_rows() -> Vec<MyRow> {
+    vec![
+        MyRow {
+            id: 1,
+            var: MyRowVariant::Array(vec![1, 2]),
+        },
+        MyRow {
+            id: 2,
+            var: MyRowVariant::Boolean(true),
+        },
+        MyRow {
+            id: 3,
+            var: MyRowVariant::Date(
+                time::Date::from_calendar_date(2021, time::Month::January, 1).unwrap(),
+            ),
+        },
+        MyRow {
+            id: 4,
+            var: MyRowVariant::FixedString(*b"foobar"),
+        },
+        MyRow {
+            id: 5,
+            var: MyRowVariant::Float32(100.5),
+        },
+        MyRow {
+            id: 6,
+            var: MyRowVariant::Float64(200.1),
+        },
+        MyRow {
+            id: 7,
+            var: MyRowVariant::Int8(2),
+        },
+        MyRow {
+            id: 8,
+            var: MyRowVariant::Int16(3),
+        },
+        MyRow {
+            id: 9,
+            var: MyRowVariant::Int32(4),
+        },
+        MyRow {
+            id: 10,
+            var: MyRowVariant::Int64(5),
+        },
+        MyRow {
+            id: 11,
+            var: MyRowVariant::Int128(6),
+        },
+        MyRow {
+            id: 12,
+            var: MyRowVariant::String("my_string".to_string()),
+        },
+        MyRow {
+            id: 13,
+            var: MyRowVariant::UInt8(7),
+        },
+        MyRow {
+            id: 14,
+            var: MyRowVariant::UInt16(8),
+        },
+        MyRow {
+            id: 15,
+            var: MyRowVariant::UInt32(9),
+        },
+        MyRow {
+            id: 16,
+            var: MyRowVariant::UInt64(10),
+        },
+        MyRow {
+            id: 17,
+            var: MyRowVariant::UInt128(11),
+        },
+    ]
+}
+
+// As the inner Variant types are _always_ sorted alphabetically,
+// Rust enum variants should be defined in the _exactly_ same order as it is in the data type;
+// their names are irrelevant, only the order of the types matters.
+// This enum represents Variant(Array(UInt16), Bool, Date, FixedString(6), Float32, Float64, Int128, Int16, Int32, Int64, Int8, String, UInt128, UInt16, UInt32, UInt64, UInt8)
+#[derive(Debug, PartialEq, Serialize, Deserialize)]
+enum MyRowVariant {
+    Array(Vec<i16>),
+    Boolean(bool),
+    // attributes should work in this case, too
+    #[serde(with = "clickhouse::serde::time::date")]
+    Date(time::Date),
+    // NB: by default, fetched as raw bytes
+    FixedString([u8; 6]),
+    Float32(f32),
+    Float64(f64),
+    Int128(i128),
+    Int16(i16),
+    Int32(i32),
+    Int64(i64),
+    Int8(i8),
+    String(String),
+    UInt128(u128),
+    UInt16(i16),
+    UInt32(u32),
+    UInt64(u64),
+    UInt8(i8),
+}
+
+#[derive(Debug, PartialEq, Row, Serialize, Deserialize)]
+struct MyRow {
+    id: u64,
+    var: MyRowVariant,
+}

src/error.rs

@@ -32,12 +32,16 @@ pub enum Error {
     InvalidUtf8Encoding(#[from] Utf8Error),
     #[error("tag for enum is not valid")]
     InvalidTagEncoding(usize),
+    #[error("max number of types in the Variant data type is 255, got {0}")]
+    VariantDiscriminatorIsOutOfBound(usize),
     #[error("a custom error message from serde: {0}")]
     Custom(String),
     #[error("bad response: {0}")]
     BadResponse(String),
     #[error("timeout expired")]
     TimedOut,
+    #[error("unsupported: {0}")]
+    Unsupported(String),
 }
 
 assert_impl_all!(Error: StdError, Send, Sync);

src/rowbinary/de.rs

@@ -1,13 +1,13 @@
 use std::{convert::TryFrom, mem, str};
 
+use crate::error::{Error, Result};
 use bytes::Buf;
+use serde::de::{EnumAccess, VariantAccess};
 use serde::{
     de::{DeserializeSeed, Deserializer, SeqAccess, Visitor},
     Deserialize,
 };
 
-use crate::error::{Error, Result};
-
 /// Deserializes a value from `input` with a row encoded in `RowBinary`.
 ///
 /// It accepts _a reference to_ a byte slice because it somehow leads to a more
@@ -146,14 +146,73 @@ impl<'cursor, 'data> Deserializer<'data> for &mut RowBinaryDeserializer<'cursor,
         visitor.visit_byte_buf(self.read_vec(size)?)
     }
 
+    #[inline]
+    fn deserialize_identifier<V: Visitor<'data>>(self, visitor: V) -> Result<V::Value> {
+        self.deserialize_u8(visitor)
+    }
+
     #[inline]
     fn deserialize_enum<V: Visitor<'data>>(
         self,
-        name: &'static str,
+        _name: &'static str,
         _variants: &'static [&'static str],
-        _visitor: V,
+        visitor: V,
     ) -> Result<V::Value> {
-        panic!("enums are unsupported: `{name}`");
+        struct Access<'de, 'cursor, 'data> {
+            deserializer: &'de mut RowBinaryDeserializer<'cursor, 'data>,
+        }
+        struct VariantDeserializer<'de, 'cursor, 'data> {
+            deserializer: &'de mut RowBinaryDeserializer<'cursor, 'data>,
+        }
+        impl<'data> VariantAccess<'data> for VariantDeserializer<'_, '_, 'data> {
+            type Error = Error;
+
+            fn unit_variant(self) -> Result<()> {
+                Err(Error::Unsupported("unit variants".to_string()))
+            }
+
+            fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value>
+            where
+                T: DeserializeSeed<'data>,
+            {
+                DeserializeSeed::deserialize(seed, &mut *self.deserializer)
+            }
+
+            fn tuple_variant<V>(self, len: usize, visitor: V) -> Result<V::Value>
+            where
+                V: Visitor<'data>,
+            {
+                self.deserializer.deserialize_tuple(len, visitor)
+            }
+
+            fn struct_variant<V>(
+                self,
+                fields: &'static [&'static str],
+                visitor: V,
+            ) -> Result<V::Value>
+            where
+                V: Visitor<'data>,
+            {
+                self.deserializer.deserialize_tuple(fields.len(), visitor)
+            }
+        }
+
+        impl<'de, 'cursor, 'data> EnumAccess<'data> for Access<'de, 'cursor, 'data> {
+            type Error = Error;
+            type Variant = VariantDeserializer<'de, 'cursor, 'data>;
+
+            fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant), Self::Error>
+            where
+                T: DeserializeSeed<'data>,
+            {
+                let value = seed.deserialize(&mut *self.deserializer)?;
+                let deserializer = VariantDeserializer {
+                    deserializer: self.deserializer,
+                };
+                Ok((value, deserializer))
+            }
+        }
+        visitor.visit_enum(Access { deserializer: self })
     }
 
     #[inline]
@@ -222,11 +281,6 @@ impl<'cursor, 'data> Deserializer<'data> for &mut RowBinaryDeserializer<'cursor,
         self.deserialize_tuple(fields.len(), visitor)
     }
 
-    #[inline]
-    fn deserialize_identifier<V: Visitor<'data>>(self, _visitor: V) -> Result<V::Value> {
-        panic!("identifiers are unsupported");
-    }
-
     #[inline]
     fn deserialize_newtype_struct<V: Visitor<'data>>(
         self,

src/rowbinary/ser.rs

@@ -134,12 +134,26 @@ impl<'a, B: BufMut> Serializer for &'a mut RowBinarySerializer<B> {
     #[inline]
     fn serialize_newtype_variant<T: Serialize + ?Sized>(
         self,
-        name: &'static str,
-        _variant_index: u32,
-        variant: &'static str,
-        _value: &T,
+        _name: &'static str,
+        variant_index: u32,
+        _variant: &'static str,
+        value: &T,
     ) -> Result<()> {
-        panic!("newtype variant types are unsupported: `{name}::{variant}`");
+        // TODO:
+        //  - Now this code implicitly allows using enums at the top level.
+        //    However, instead of a more descriptive panic, it ends with a "not enough data." error.
+        //  - Also, it produces an unclear message for a forgotten `serde_repr` (Enum8 and Enum16).
+        //  See https://github.com/ClickHouse/clickhouse-rs/pull/170#discussion_r1848549636
+
+        // Max number of types in the Variant data type is 255
+        // See also: https://github.com/ClickHouse/ClickHouse/issues/54864
+        if variant_index > 255 {
+            return Err(Error::VariantDiscriminatorIsOutOfBound(
+                variant_index as usize,
+            ));
+        }
+        self.buffer.put_u8(variant_index as u8);
+        value.serialize(self)
     }
 
     #[inline]

tests/it/main.rs

@@ -66,6 +66,7 @@ mod query;
 mod time;
 mod user_agent;
 mod uuid;
+mod variant;
 mod watch;
 
 const HOST: &str = "localhost:8123";