Trait DrizzleSQLiteColumn

Source

pub trait DrizzleSQLiteColumn: Sized {
    type SQLType: SQLiteAffinity;

    const SQL_TYPE: &'static str = <Self::SQLType as SQLiteAffinity>::SQL_TYPE;

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

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

Expand description

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

#[derive(SQLiteEnum)] implements this for enums. Implement it by hand to use your own type as a field of a #[SQLiteTable]: SQLType picks the column’s affinity, decode reads a cell, and encode writes one. Implementing it also gives the type FromSQLiteValue and From<T> for SQLiteValue.

From<T> for SQLiteValue goes through encode_owned, because insert and update models keep their values after the source is dropped. Override encode_owned when the type can hand over its buffer without copying.

§Examples

A u32 stored as four big-endian bytes:

use drizzle_core::error::DrizzleError;
use drizzle_sqlite::traits::{DrizzleSQLiteColumn, FromSQLiteValue};
use drizzle_sqlite::types::Blob;
use drizzle_sqlite::values::{SQLiteValue, SQLiteValueRef};
use std::borrow::Cow;

struct U32Be(u32);

impl DrizzleSQLiteColumn for U32Be {
    type SQLType = Blob;

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

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

let value = SQLiteValue::from(U32Be(7));
assert_eq!(value, SQLiteValue::Blob(Cow::Borrowed(&[0, 0, 0, 7][..])));
assert_eq!(U32Be::from_sqlite_blob(&[0, 0, 1, 0]).unwrap().0, 256);
assert!(U32Be::from_sqlite_text("7").is_err());