Trait DrizzleMySQLColumn

Source

pub trait DrizzleMySQLColumn: Sized {
    type SQLType: MySQLColumnType;

    const SQL_TYPE: &'static str;

    // Required methods
    fn decode(value: MySQLValue<'_>) -> Result<Self, DrizzleError>;
    fn encode(&self) -> MySQLValue<'_>;

    // Provided method
    fn encode_owned(self) -> OwnedMySQLValue { ... }
}

Expand description

A Rust type that can be stored in a MySQL column.

Implement it to use your own type as a field of a #[MySQLTable]. SQLType sets which expressions the column can be used in, SQL_TYPE is written into the DDL, and decode / encode convert values. Implementing it also gives From<T> for MySQLValue, which goes through encode_owned.

§Examples

A u32 stored as four big-endian bytes:

use drizzle_core::error::DrizzleError;
use drizzle_mysql::traits::DrizzleMySQLColumn;
use drizzle_mysql::types::Binary;
use drizzle_mysql::values::MySQLValue;
use std::borrow::Cow;

struct U32Be(u32);

impl DrizzleMySQLColumn for U32Be {
    type SQLType = Binary;
    const SQL_TYPE: &'static str = "BINARY(4)";

    fn decode(value: MySQLValue<'_>) -> Result<Self, DrizzleError> {
        let MySQLValue::Bytes(bytes) = value else {
            return Err(DrizzleError::ConversionError("expected bytes".into()));
        };
        let bytes: [u8; 4] = bytes
            .as_ref()
            .try_into()
            .map_err(|_| DrizzleError::ConversionError("expected 4 bytes".into()))?;
        Ok(Self(u32::from_be_bytes(bytes)))
    }

    fn encode(&self) -> MySQLValue<'_> {
        MySQLValue::Bytes(Cow::Owned(self.0.to_be_bytes().to_vec()))
    }
}

let value = MySQLValue::from(U32Be(7));
assert_eq!(value, MySQLValue::Bytes(Cow::Borrowed(&[0, 0, 0, 7][..])));
assert_eq!(U32Be::decode(value).unwrap().0, 7);
assert!(U32Be::decode(MySQLValue::Int(7)).is_err());