pub trait QueryableByName<DB> where
    Self: Sized,
    DB: Backend
{ fn build<R: NamedRow<DB>>(row: &R) -> Result<Self>; }
Expand description

Deserializes the result of a query constructed with sql_query.

Deriving

To derive this trait, Diesel needs to know the SQL type of each field. You can do this by either annotating your struct with #[table_name = "some_table"] (in which case the SQL type will be diesel::dsl::SqlTypeOf<table_name::column_name>), or by annotating each field with #[sql_type = "SomeType"].

If you are using #[table_name], the module for that table must be in scope. For example, to derive this for a struct called User, you will likely need a line such as use schema::users;

If the name of a field on your struct is different than the column in your table! declaration, or if you are deriving this trait on a tuple struct, you can annotate the field with #[column_name = "some_column"]. For tuple structs, all fields must have this annotation.

If a field is another struct which implements QueryableByName, instead of a column, you can annotate that struct with #[diesel(embed)]

To provide custom deserialization behavior for a field, you can use #[diesel(deserialize_as = "Type")]. If this attribute is present, Diesel will deserialize into that type, rather than the type on your struct and call .into to convert it. This can be used to add custom behavior for a single field, or use types that are otherwise unsupported by Diesel.

Examples

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

#[derive(QueryableByName, PartialEq, Debug)]
#[table_name = "users"]
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: Option<&DB::RawValue>) -> deserialize::Result<Self> {
        String::from_sql(bytes)
            .map(|s| LowercaseString(s.to_lowercase()))
    }
}

#[derive(QueryableByName, PartialEq, Debug)]
#[table_name = "users"]
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

Construct an instance of Self from the database row

Implementations on Foreign Types

Implementors