Module dynamic_value 

This module provides a container that allows to receive a dynamically specified number of fields from the database.

    let users = diesel_dynamic_schema::table("users");
    let id = users.column::<Untyped, _>("id");
    let name = users.column::<Untyped, _>("name");

    let mut select = DynamicSelectClause::new();

    select.add_field(id);
    select.add_field(name);

    let actual_data: Vec<DynamicRow<NamedField<MyDynamicValue>>> =
        users.select(select).load(conn)?;

    assert_eq!(
        actual_data[0]["name"],
        MyDynamicValue::String("Sean".into())
    );
    assert_eq!(
        actual_data[0][1],
        NamedField {
            name: "name".into(),
            value: MyDynamicValue::String("Sean".into())
        }
    );

It is required to provide your own inner type to hold the actual database value.

#[derive(PartialEq, Debug)]
enum MyDynamicValue {
    String(String),
    Integer(i32),
}

impl FromSql<Any, diesel::pg::Pg> for MyDynamicValue {
    fn from_sql(value: diesel::pg::PgValue) -> deserialize::Result<Self> {
        use diesel::pg::Pg;
        use std::num::NonZeroU32;

        const VARCHAR_OID: NonZeroU32 = unsafe { NonZeroU32::new_unchecked(1043) };
        const TEXT_OID: NonZeroU32 = unsafe { NonZeroU32::new_unchecked(25) };
        const INTEGER_OID: NonZeroU32 = unsafe { NonZeroU32::new_unchecked(23) };

        match value.get_oid() {
            VARCHAR_OID | TEXT_OID => {
                <String as FromSql<diesel::sql_types::Text, Pg>>::from_sql(value)
                    .map(MyDynamicValue::String)
            }
            INTEGER_OID => <i32 as FromSql<diesel::sql_types::Integer, Pg>>::from_sql(value)
                .map(MyDynamicValue::Integer),
            e => Err(format!("Unknown type: {}", e).into()),
        }
    }
}

Structs

Any

A marker type used to indicate that the provided FromSql impl does handle any passed database value, independently from the actual value kind

DynamicRow

A dynamically sized container that allows to receive a not at compile time known number of columns from the database

NamedField

A helper struct used as field type in DynamicRow to also return the name of the field along with the value