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//! Types and traits related to deserializing values from the database
use std::error::Error;
use std::result;
use crate::backend::{self, Backend};
use crate::expression::select_by::SelectBy;
use crate::row::{NamedRow, Row};
use crate::sql_types::{SingleValue, SqlType, Untyped};
use crate::Selectable;
/// A specialized result type representing the result of deserializing
/// a value from the database.
pub type Result<T> = result::Result<T, Box<dyn Error + Send + Sync>>;
/// Trait indicating that a record can be queried from the database.
///
/// Types which implement `Queryable` represent the result of a SQL query. This
/// does not necessarily mean they represent a single database table.
///
/// Diesel represents the return type of a query as a tuple. The purpose of this
/// trait is to convert from a tuple of Rust values that have been deserialized
/// into your struct.
///
/// This trait can be [derived](derive@Queryable)
///
/// ## Interaction with `NULL`/`Option`
/// [`Nullable`][crate::sql_types::Nullable] types can be queried into `Option`.
/// This is valid for single fields, tuples, and structures with `Queryable`.
///
/// With tuples and structs, the process for deserializing an `Option<(A,B,C)>` is
/// to attempt to deserialize `A`, `B` and `C`, and if either of these return an
/// [`UnexpectedNullError`](crate::result::UnexpectedNullError), the `Option` will be
/// deserialized as `None`.
/// If all succeed, the `Option` will be deserialized as `Some((a,b,c))`.
///
/// # Examples
///
/// ## Simple mapping from query to struct
///
/// If we just want to map a query to our struct, we can use `derive`.
///
/// ```rust
/// # include!("doctest_setup.rs");
/// #
/// #[derive(Queryable, PartialEq, Debug)]
/// struct User {
/// id: i32,
/// name: String,
/// }
///
/// # fn main() {
/// # run_test();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # use schema::users::dsl::*;
/// # let connection = &mut establish_connection();
/// let first_user = users.order_by(id).first(connection)?;
/// let expected = User { id: 1, name: "Sean".into() };
/// assert_eq!(expected, first_user);
/// # Ok(())
/// # }
/// ```
///
/// ## Interaction with `NULL`/`Option`
///
/// ### Single field
/// ```rust
/// # include!("doctest_setup.rs");
/// # use diesel::sql_types::*;
/// #
/// table! {
/// animals {
/// id -> Integer,
/// species -> VarChar,
/// legs -> Integer,
/// name -> Nullable<VarChar>,
/// }
/// }
/// #
/// #[derive(Queryable, PartialEq, Debug)]
/// struct Animal {
/// id: i32,
/// name: Option<String>,
/// }
///
/// # fn main() {
/// # run_test();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # use schema::animals::dsl::*;
/// # let connection = &mut establish_connection();
/// let all_animals = animals.select((id, name)).order_by(id).load(connection)?;
/// let expected = vec![Animal { id: 1, name: Some("Jack".to_owned()) }, Animal { id: 2, name: None }];
/// assert_eq!(expected, all_animals);
/// # Ok(())
/// # }
/// ```
///
/// ### Multiple fields
/// ```rust
/// # include!("doctest_setup.rs");
/// #
/// #[derive(Queryable, PartialEq, Debug)]
/// struct UserWithPost {
/// id: i32,
/// post: Option<Post>,
/// }
/// #[derive(Queryable, PartialEq, Debug)]
/// struct Post {
/// id: i32,
/// title: String,
/// }
///
/// # fn main() {
/// # run_test();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # use schema::{posts, users};
/// # let connection = &mut establish_connection();
/// # diesel::insert_into(users::table)
/// # .values(users::name.eq("Ruby"))
/// # .execute(connection)?;
/// let all_posts = users::table
/// .left_join(posts::table)
/// .select((
/// users::id,
/// (posts::id, posts::title).nullable()
/// ))
/// .order_by((users::id, posts::id))
/// .load(connection)?;
/// let expected = vec![
/// UserWithPost { id: 1, post: Some(Post { id: 1, title: "My first post".to_owned() }) },
/// UserWithPost { id: 1, post: Some(Post { id: 2, title: "About Rust".to_owned() }) },
/// UserWithPost { id: 2, post: Some(Post { id: 3, title: "My first post too".to_owned() }) },
/// UserWithPost { id: 3, post: None },
/// ];
/// assert_eq!(expected, all_posts);
/// # Ok(())
/// # }
/// ```
///
/// ## `deserialize_as` attribute
///
/// If we want to do additional work during deserialization, we can use
/// `deserialize_as` to use a different implementation.
///
/// ```rust
/// # include!("doctest_setup.rs");
/// #
/// # use schema::users;
/// # use diesel::backend::{self, Backend};
/// # use diesel::deserialize::{self, Queryable, FromSql};
/// # use diesel::sql_types::Text;
/// #
/// struct LowercaseString(String);
///
/// impl Into<String> for LowercaseString {
/// fn into(self) -> String {
/// self.0
/// }
/// }
///
/// impl<DB> Queryable<Text, DB> for LowercaseString
/// where
/// DB: Backend,
/// String: FromSql<Text, DB>,
/// {
/// type Row = String;
///
/// fn build(s: String) -> deserialize::Result<Self> {
/// Ok(LowercaseString(s.to_lowercase()))
/// }
/// }
///
/// #[derive(Queryable, PartialEq, Debug)]
/// struct User {
/// id: i32,
/// #[diesel(deserialize_as = LowercaseString)]
/// name: String,
/// }
///
/// # fn main() {
/// # run_test();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # use schema::users::dsl::*;
/// # let connection = &mut establish_connection();
/// let first_user = users.first(connection)?;
/// let expected = User { id: 1, name: "sean".into() };
/// assert_eq!(expected, first_user);
/// # Ok(())
/// # }
/// ```
///
/// ## Manual implementation
///
/// Alternatively, we can implement the trait for our struct manually.
///
/// ```rust
/// # include!("doctest_setup.rs");
/// #
/// use schema::users;
/// use diesel::deserialize::{self, Queryable};
///
/// # /*
/// type DB = diesel::sqlite::Sqlite;
/// # */
///
/// #[derive(PartialEq, Debug)]
/// struct User {
/// id: i32,
/// name: String,
/// }
///
/// impl Queryable<users::SqlType, DB> for User {
/// type Row = (i32, String);
///
/// fn build(row: Self::Row) -> deserialize::Result<Self> {
/// Ok(User {
/// id: row.0,
/// name: row.1.to_lowercase(),
/// })
/// }
/// }
///
/// # fn main() {
/// # run_test();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # use schema::users::dsl::*;
/// # let connection = &mut establish_connection();
/// let first_user = users.first(connection)?;
/// let expected = User { id: 1, name: "sean".into() };
/// assert_eq!(expected, first_user);
/// # Ok(())
/// # }
/// ```
pub trait Queryable<ST, DB>: Sized
where
DB: Backend,
{
/// The Rust type you'd like to map from.
///
/// This is typically a tuple of all of your struct's fields.
type Row: FromStaticSqlRow<ST, DB>;
/// Construct an instance of this type
fn build(row: Self::Row) -> Result<Self>;
}
#[doc(inline)]
pub use diesel_derives::Queryable;
/// Deserializes the result of a query constructed with [`sql_query`].
///
/// This trait can be [derived](derive@QueryableByName)
///
/// [`sql_query`]: crate::sql_query()
///
/// # Examples
///
/// If we just want to map a query to our struct, we can use `derive`.
///
/// ```rust
/// # include!("doctest_setup.rs");
/// # use schema::users;
/// # use diesel::sql_query;
/// #
/// #[derive(QueryableByName, PartialEq, Debug)]
/// #[diesel(table_name = users)]
/// struct User {
/// id: i32,
/// name: String,
/// }
///
/// # fn main() {
/// # run_test();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # let connection = &mut establish_connection();
/// 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);
/// # Ok(())
/// # }
/// ```
///
/// If we want to do additional work during deserialization, we can use
/// `deserialize_as` to use a different implementation.
///
/// ```rust
/// # include!("doctest_setup.rs");
/// # use diesel::sql_query;
/// # use schema::users;
/// # use diesel::backend::{self, Backend};
/// # use diesel::deserialize::{self, FromSql};
/// #
/// 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: backend::RawValue<DB>) -> deserialize::Result<Self> {
/// String::from_sql(bytes)
/// .map(|s| LowercaseString(s.to_lowercase()))
/// }
/// }
///
/// #[derive(QueryableByName, PartialEq, Debug)]
/// #[diesel(table_name = users)]
/// struct User {
/// id: i32,
/// #[diesel(deserialize_as = LowercaseString)]
/// name: String,
/// }
///
/// # fn main() {
/// # run_test();
/// # }
/// #
/// # fn run_test() -> QueryResult<()> {
/// # let connection = &mut establish_connection();
/// 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);
/// # Ok(())
/// # }
/// ```
pub trait QueryableByName<DB>
where
Self: Sized,
DB: Backend,
{
/// Construct an instance of `Self` from the database row
fn build<'a>(row: &impl NamedRow<'a, DB>) -> Result<Self>;
}
#[doc(inline)]
pub use diesel_derives::QueryableByName;
/// Deserialize a single field of a given SQL type.
///
/// When possible, implementations of this trait should prefer to use an
/// existing implementation, rather than reading from `bytes`. (For example, if
/// you are implementing this for an enum which is represented as an integer in
/// the database, prefer `i32::from_sql(bytes)` (or the explicit form
/// `<i32 as FromSql<Integer, DB>>::from_sql(bytes)`) over reading from `bytes`
/// directly)
///
/// Types which implement this trait should also have `#[derive(FromSqlRow)]`
///
/// ### Backend specific details
///
/// - For PostgreSQL, the bytes will be sent using the binary protocol, not text.
/// - For SQLite, the actual type of `DB::RawValue` is private API. All
/// implementations of this trait must be written in terms of an existing
/// primitive.
/// - For MySQL, the value of `bytes` will depend on the return value of
/// `type_metadata` for the given SQL type. See [`MysqlType`] for details.
/// - For third party backends, consult that backend's documentation.
///
/// [`MysqlType`]: ../mysql/enum.MysqlType.html
///
/// ### Examples
///
/// Most implementations of this trait will be defined in terms of an existing
/// implementation.
///
/// ```rust
/// # use diesel::backend::{self, Backend};
/// # use diesel::sql_types::*;
/// # use diesel::deserialize::{self, FromSql, FromSqlRow};
/// #
/// #[repr(i32)]
/// #[derive(Debug, Clone, Copy, FromSqlRow)]
/// pub enum MyEnum {
/// A = 1,
/// B = 2,
/// }
///
/// impl<DB> FromSql<Integer, DB> for MyEnum
/// where
/// DB: Backend,
/// i32: FromSql<Integer, DB>,
/// {
/// fn from_sql(bytes: backend::RawValue<DB>) -> deserialize::Result<Self> {
/// match i32::from_sql(bytes)? {
/// 1 => Ok(MyEnum::A),
/// 2 => Ok(MyEnum::B),
/// x => Err(format!("Unrecognized variant {}", x).into()),
/// }
/// }
/// }
/// ```
pub trait FromSql<A, DB: Backend>: Sized {
/// See the trait documentation.
fn from_sql(bytes: backend::RawValue<'_, DB>) -> Result<Self>;
/// A specialized variant of `from_sql` for handling null values.
///
/// The default implementation returns an `UnexpectedNullError` for
/// an encountered null value and calls `Self::from_sql` otherwise
///
/// If your custom type supports null values you need to provide a
/// custom implementation.
#[inline(always)]
fn from_nullable_sql(bytes: Option<backend::RawValue<'_, DB>>) -> Result<Self> {
match bytes {
Some(bytes) => Self::from_sql(bytes),
None => Err(Box::new(crate::result::UnexpectedNullError)),
}
}
}
/// Deserialize a database row into a rust data structure
///
/// Diesel provides wild card implementations of this trait for all types
/// that implement one of the following traits:
/// * [`Queryable`]
/// * [`QueryableByName`]
#[cfg_attr(
feature = "nightly-error-messages",
rustc_on_unimplemented(on(
ST = "diesel::sql_types::Untyped",
note = "`diesel::sql_query` requires the loading target to column names for loading values.\n\
You need to provide a type that explicitly derives `diesel::deserialize::QueryableByName`",
))
)]
pub trait FromSqlRow<ST, DB: Backend>: Sized {
/// See the trait documentation.
fn build_from_row<'a>(row: &impl Row<'a, DB>) -> Result<Self>;
}
#[doc(inline)]
pub use diesel_derives::FromSqlRow;
/// A marker trait indicating that the corresponding type consumes a static at
/// compile time known number of field
///
/// There is normally no need to implement this trait. Diesel provides
/// wild card impls for all types that implement `FromSql<ST, DB>` or `Queryable<ST, DB>`
/// where the size of `ST` is known
pub trait StaticallySizedRow<ST, DB: Backend>: FromSqlRow<ST, DB> {
/// The number of fields that this type will consume.
const FIELD_COUNT: usize;
}
impl<DB, T> FromSqlRow<Untyped, DB> for T
where
DB: Backend,
T: QueryableByName<DB>,
{
fn build_from_row<'a>(row: &impl Row<'a, DB>) -> Result<Self> {
T::build(row)
}
}
/// A helper trait to deserialize a statically sized row into an tuple
///
/// **If you see an error message mentioning this trait you likely
/// trying to map the result of an query to an struct with mismatching
/// field types. Recheck your field order and the concrete field types**
///
/// You should not need to implement this trait directly.
/// Diesel provides wild card implementations for any supported tuple size
/// and for any type that implements `FromSql<ST, DB>`.
///
// This is a distinct trait from `FromSqlRow` because otherwise we
// are getting conflicting implementation errors for our `FromSqlRow`
// implementation for tuples and our wild card impl for all types
// implementing `Queryable`
pub trait FromStaticSqlRow<ST, DB: Backend>: Sized {
/// See the trait documentation
fn build_from_row<'a>(row: &impl Row<'a, DB>) -> Result<Self>;
}
#[doc(hidden)]
pub trait SqlTypeOrSelectable {}
impl<ST> SqlTypeOrSelectable for ST where ST: SqlType + SingleValue {}
impl<U, DB> SqlTypeOrSelectable for SelectBy<U, DB>
where
U: Selectable<DB>,
DB: Backend,
{
}
impl<T, ST, DB> FromSqlRow<ST, DB> for T
where
T: Queryable<ST, DB>,
ST: SqlTypeOrSelectable,
DB: Backend,
T::Row: FromStaticSqlRow<ST, DB>,
{
// This inline(always) attribute is here as benchmarks have shown
// a up to 5% reduction in instruction count of having it here
//
// A plain inline attribute does not show similar improvements
#[inline(always)]
fn build_from_row<'a>(row: &impl Row<'a, DB>) -> Result<Self> {
let row = <T::Row as FromStaticSqlRow<ST, DB>>::build_from_row(row)?;
T::build(row)
}
}
impl<T, ST, DB> FromStaticSqlRow<ST, DB> for T
where
DB: Backend,
T: FromSql<ST, DB>,
ST: SingleValue,
{
fn build_from_row<'a>(row: &impl Row<'a, DB>) -> Result<Self> {
use crate::row::Field;
let field = row.get(0).ok_or(crate::result::UnexpectedEndOfRow)?;
T::from_nullable_sql(field.value())
}
}
// We cannot have this impl because rustc
// then complains in third party crates that
// diesel may implement `SingleValue` for tuples
// in the future. While that is theoretically true,
// that will likely not happen in practice.
// If we get negative trait impls at some point in time
// it should be possible to make this work.
/*impl<T, ST, DB> Queryable<ST, DB> for T
where
DB: Backend,
T: FromStaticSqlRow<ST, DB>,
ST: SingleValue,
{
type Row = Self;
fn build(row: Self::Row) -> Self {
row
}
}*/
impl<T, ST, DB> StaticallySizedRow<ST, DB> for T
where
ST: SqlTypeOrSelectable + crate::util::TupleSize,
T: Queryable<ST, DB>,
DB: Backend,
{
const FIELD_COUNT: usize = <ST as crate::util::TupleSize>::SIZE;
}