Trait diesel::deserialize::QueryableByName
source · [−]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);