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use crate::database::Database;
use either::Either;
use std::convert::identity;
/// Provides extended information on a statement.
///
/// Returned from [`Executor::describe`].
///
/// The query macros (e.g., `query!`, `query_as!`, etc.) use the information here to validate
/// output and parameter types; and, generate an anonymous record.
#[derive(Debug,serde::Serialize, serde::Deserialize)]
#[serde(bound(
serialize = "DB::TypeInfo: serde::Serialize, DB::Column: serde::Serialize",
deserialize = "DB::TypeInfo: serde::de::DeserializeOwned, DB::Column: serde::de::DeserializeOwned",
))]
#[doc(hidden)]
pub struct Describe<DB: Database> {
pub columns: Vec<DB::Column>,
pub parameters: Option<Either<Vec<DB::TypeInfo>, usize>>,
pub nullable: Vec<Option<bool>>,
}
impl<DB: Database> Describe<DB> {
/// Gets all columns in this statement.
pub fn columns(&self) -> &[DB::Column] {
&self.columns
}
/// Gets the column information at `index`.
///
/// Panics if `index` is out of bounds.
pub fn column(&self, index: usize) -> &DB::Column {
&self.columns[index]
}
/// Gets the available information for parameters in this statement.
///
/// Some drivers may return more or less than others. As an example, **PostgreSQL** will
/// return `Some(Either::Left(_))` with a full list of type information for each parameter.
/// However, **MSSQL** will return `None` as there is no information available.
pub fn parameters(&self) -> Option<Either<&[DB::TypeInfo], usize>> {
self.parameters.as_ref().map(|p| match p {
Either::Left(params) => Either::Left(&**params),
Either::Right(count) => Either::Right(*count),
})
}
/// Gets whether a column may be `NULL`, if this information is available.
pub fn nullable(&self, column: usize) -> Option<bool> {
self.nullable.get(column).copied().and_then(identity)
}
}