Trait Type

pub trait Type<DB>where
    DB: Database,{
    // Required method
    fn type_info() -> <DB as Database>::TypeInfo;

    // Provided method
    fn compatible(ty: &<DB as Database>::TypeInfo) -> bool { ... }
}

Expand description

Indicates that a SQL type is supported for a database.

§Compile-time verification

Type definitions are not verified against the database at compile-time. The query!() macros have no implicit knowledge of user-defined types.

When using custom types in query parameters or output columns with query!(), the use of type overrides is required.

struct MyUser { id: UserId, name: String }

// fetch all properties from user and override the type in Rust for `id`
let user = query_as!(MyUser, r#"SELECT users.*, id as "id: UserId" FROM users"#)
    .fetch_one(&pool).await?;

§Derivable

This trait can be derived by SQLx to support Rust-only wrapper types, enumerations, and (for postgres) structured records. Additionally, an implementation of Encode and Decode is generated.

§Transparent

Rust-only domain wrappers around SQL types. The generated implementations directly delegate to the implementation of the inner type.

#[derive(sqlx::Type)]
#[sqlx(transparent)]
struct UserId(i64);

§Note: `PgHasArrayType`

If you have the postgres feature enabled, this derive also generates a PgHasArrayType impl so that you may use it with Vec and other types that decode from an array in Postgres:

let user_ids: Vec<UserId> = sqlx::query_scalar("select '{ 123, 456 }'::int8[]")
   .fetch(&mut pg_connection)
   .await?;

However, if you are wrapping a type that does not implement PgHasArrayType (e.g. Vec itself, because we don’t currently support multidimensional arrays), you may receive an error:

#[derive(sqlx::Type)] // ERROR: `Vec<i64>` does not implement `PgHasArrayType`
#[sqlx(transparent)]
struct UserIds(Vec<i64>);

To remedy this, add #[sqlx(no_pg_array)], which disables the generation of the PgHasArrayType impl:

#[derive(sqlx::Type)]
#[sqlx(transparent, no_pg_array)]
struct UserIds(Vec<i64>);

§Attributes

#[sqlx(type_name = "<SQL type name>")] on struct definition: instead of inferring the SQL type name from the inner field (in the above case, BIGINT), explicitly set it to <SQL type name> instead. May trigger errors or unexpected behavior if the encoding of the given type is different than that of the inferred type (e.g. if you rename the above to VARCHAR). Affects Postgres only.
#[sqlx(rename_all = "<strategy>")] on struct definition: See derive docs in FromRow
#[sqlx(no_pg_array)]: do not emit a PgHasArrayType impl (see above).

§Enumeration

Enumerations may be defined in Rust and can match SQL by integer discriminant or variant name.

With #[repr(_)] the integer representation is used when converting from/to SQL and expects that SQL type (e.g., INT). Without, the names of the variants are used instead and expects a textual SQL type (e.g., VARCHAR, TEXT).

#[derive(sqlx::Type)]
#[repr(i32)]
enum Color { Red = 1, Green = 2, Blue = 3 }

#[derive(sqlx::Type)]
#[sqlx(type_name = "color")] // only for PostgreSQL to match a type definition
#[sqlx(rename_all = "lowercase")]
enum Color { Red, Green, Blue }

§Records

User-defined composite types are supported through deriving a struct.

This is only supported for PostgreSQL.

#[derive(sqlx::Type)]
#[sqlx(type_name = "interface_type")]
struct InterfaceType {
    name: String,
    supplier_id: i32,
    price: f64
}

Required Methods§

fn type_info() -> <DB as Database>::TypeInfo

Returns the canonical SQL type for this Rust type.

When binding arguments, this is used to tell the database what is about to be sent; which, the database then uses to guide query plans. This can be overridden by Encode::produces.

A map of SQL types to Rust types is populated with this and used to determine the type that is returned from the anonymous struct type from query!.