Crate xxai_postgres_types

Conversions to and from Postgres types.

This crate is used by the tokio-postgres and postgres crates. You normally don’t need to depend directly on it unless you want to define your own ToSql or FromSql definitions.

Derive

If the derive cargo feature is enabled, you can derive ToSql and FromSql implementations for custom Postgres types. Explicitly, modify your Cargo.toml file to include the following:

[dependencies]
postgres-types = { version = "0.X.X", features = ["derive"] }

Enums

Postgres enums correspond to C-like enums in Rust:

CREATE TYPE "Mood" AS ENUM (
    'Sad',
    'Ok',
    'Happy'
);

use postgres_types::{ToSql, FromSql};

#[derive(Debug, ToSql, FromSql)]
enum Mood {
    Sad,
    Ok,
    Happy,
}

Domains

Postgres domains correspond to tuple structs with one member in Rust:

CREATE DOMAIN "SessionId" AS BYTEA CHECK(octet_length(VALUE) = 16);

use postgres_types::{ToSql, FromSql};

#[derive(Debug, ToSql, FromSql)]
struct SessionId(Vec<u8>);

Newtypes

The #[postgres(transparent)] attribute can be used on a single-field tuple struct to create a Rust-only wrapper type that will use the ToSql & FromSql implementation of the inner value :

use postgres_types::{ToSql, FromSql};

#[derive(Debug, ToSql, FromSql)]
#[postgres(transparent)]
struct UserId(i32);

Composites

Postgres composite types correspond to structs in Rust:

CREATE TYPE "InventoryItem" AS (
    name TEXT,
    supplier_id INT,
    price DOUBLE PRECISION
);

use postgres_types::{ToSql, FromSql};

#[derive(Debug, ToSql, FromSql)]
struct InventoryItem {
    name: String,
    supplier_id: i32,
    price: Option<f64>,
}

Naming

The derived implementations will enforce exact matches of type, field, and variant names between the Rust and Postgres types. The #[postgres(name = "...")] attribute can be used to adjust the name on a type, variant, or field:

CREATE TYPE mood AS ENUM (
    'sad',
    'ok',
    'happy'
);

use postgres_types::{ToSql, FromSql};

#[derive(Debug, ToSql, FromSql)]
#[postgres(name = "mood")]
enum Mood {
    #[postgres(name = "sad")]
    Sad,
    #[postgres(name = "ok")]
    Ok,
    #[postgres(name = "happy")]
    Happy,
}

Alternatively, the #[postgres(rename_all = "...")] attribute can be used to rename all fields or variants with the chosen casing convention. This will not affect the struct or enum’s type name. Note that #[postgres(name = "...")] takes precendence when used in conjunction with #[postgres(rename_all = "...")]:

use postgres_types::{ToSql, FromSql};

#[derive(Debug, ToSql, FromSql)]
#[postgres(name = "mood", rename_all = "snake_case")]
enum Mood {
    #[postgres(name = "ok")]
    Ok,             // ok
    VeryHappy,      // very_happy
}

The following case conventions are supported:

• "lowercase"
• "UPPERCASE"
• "PascalCase"
• "camelCase"
• "snake_case"
• "SCREAMING_SNAKE_CASE"
• "kebab-case"
• "SCREAMING-KEBAB-CASE"
• "Train-Case"

Allowing Enum Mismatches

By default the generated implementation of ToSql & FromSql for enums will require an exact match of the enum variants between the Rust and Postgres types. To allow mismatches, the #[postgres(allow_mismatch)] attribute can be used on the enum definition:

CREATE TYPE mood AS ENUM (
  'Sad',
  'Ok',
  'Happy'
);

#[postgres(allow_mismatch)] enum Mood { Happy, Meh, }

Macros

• accepts
  Generates a simple implementation of ToSql::accepts which accepts the types passed to it.
• to_sql_checked
  Generates an implementation of ToSql::to_sql_checked.

Structs

• Field
  Information about a field of a composite type.
• PgLsn
  Postgres PG_LSN type.
• Type
  A Postgres type.
• WasNull
  An error indicating that a NULL Postgres value was passed to a FromSql implementation that does not support NULL values.
• WrongType
  An error indicating that a conversion was attempted between incompatible Rust and Postgres types.

Enums

• Date
  A wrapper that can be used to represent infinity with Type::Date types.
• Format
  Supported Postgres message format types
• IsNull
  An enum representing the nullability of a Postgres value.
• Kind
  Represents the kind of a Postgres type.
• Timestamp
  A wrapper that can be used to represent infinity with Type::Timestamp and Type::Timestamptz types.

Traits

• BorrowToSql
  A trait used by clients to abstract over &dyn ToSql and T: ToSql.
• FromSql
  A trait for types that can be created from a Postgres value.
• FromSqlOwned
  A trait for types which can be created from a Postgres value without borrowing any data.
• ToSql
  A trait for types that can be converted into Postgres values.

Type Definitions

• Oid
  A Postgres OID.