Trait QueryableByName 

pub trait QueryableByName<DB>
where
    Self: Sized,
    DB: Backend,
{
    // Required method
    fn build<'a>(row: &impl NamedRow<'a, DB>) -> Result<Self>;
}

Deserializes the result of a query constructed with sql_query.

This trait can be derived

Examples

If we just want to map a query to our struct, we can use derive.

#[derive(QueryableByName, PartialEq, Debug)]
struct User {
    id: i32,
    name: String,
}

let first_user = sql_query("SELECT * FROM users ORDER BY id LIMIT 1").get_result(connection)?;
let expected = User {
    id: 1,
    name: "Sean".into(),
};
assert_eq!(expected, first_user);

If we want to do additional work during deserialization, we can use deserialize_as to use a different implementation.

struct LowercaseString(String);

impl Into<String> for LowercaseString {
    fn into(self) -> String {
        self.0
    }
}

impl<DB, ST> FromSql<ST, DB> for LowercaseString
where
    DB: Backend,
    String: FromSql<ST, DB>,
{
    fn from_sql(bytes: DB::RawValue<'_>) -> deserialize::Result<Self> {
        String::from_sql(bytes).map(|s| LowercaseString(s.to_lowercase()))
    }
}

#[derive(QueryableByName, PartialEq, Debug)]
struct User {
    id: i32,
    #[diesel(deserialize_as = LowercaseString)]
    name: String,
}

let first_user = sql_query("SELECT * FROM users ORDER BY id LIMIT 1").get_result(connection)?;
let expected = User {
    id: 1,
    name: "sean".into(),
};
assert_eq!(expected, first_user);

Required Methods

fn build<'a>(row: &impl NamedRow<'a, DB>) -> Result<Self>

Construct an instance of Self from the database row

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementations on Foreign Types

impl<T, DB> QueryableByName<DB> for Option<T>

where DB: Backend, T: QueryableByName<DB>,

fn build<'a>(row: &impl NamedRow<'a, DB>) -> Result<Self>

impl<T, __DB> QueryableByName<__DB> for (T₁, T₂, …, Tₙ)

where __DB: Backend, T: QueryableByName<__DB>,

fn build<'a>(row: &impl NamedRow<'a, __DB>) -> Result<Self>

Implementors