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Implement SqliteStatement::query_and_then()

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Allows for more ergonomic unification of error types
This commit is contained in:
Patrick Fernie 2015-08-27 13:43:43 -04:00
parent e1532f5edf
commit 29072e585b
1 changed files with 224 additions and 2 deletions
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224
src/lib.rs
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@ -55,6 +55,7 @@ extern crate libsqlite3_sys as ffi;
#[macro_use] extern crate bitflags;
use std::default::Default;
use std::convert;
use std::mem;
use std::ptr;
use std::fmt;
@ -90,7 +91,7 @@ unsafe fn errmsg_to_string(errmsg: *const c_char) -> String {
}
/// Encompasses an error result from a call to the SQLite C API.
#[derive(Debug)]
#[derive(Debug, PartialEq)]
pub struct SqliteError {
/// The error code returned by a SQLite C API call. See [SQLite Result
/// Codes](http://www.sqlite.org/rescode.html) for details.
@ -680,6 +681,25 @@ impl<'conn> SqliteStatement<'conn> {
})
}
/// Executes the prepared statement and maps a function over the resulting
/// rows, where the function returns a `Result` with `Error` type implementing
/// `std::convert::From<SqliteError>` (so errors can be unified).
///
/// Unlike the iterator produced by `query`, the returned iterator does not expose the possibility
/// for accessing stale rows.
pub fn query_and_then<'a, T, E, F>(&'a mut self, params: &[&ToSql], f: F)
-> SqliteResult<AndThenRows<'a, F>>
where T: 'static,
E: convert::From<SqliteError>,
F: FnMut(SqliteRow) -> Result<T, E> {
let row_iter = try!(self.query(params));
Ok(AndThenRows{
rows: row_iter,
map: f,
})
}
/// Consumes the statement.
///
/// Functionally equivalent to the `Drop` implementation, but allows callers to see any errors
@ -746,6 +766,28 @@ impl<'stmt, T, F> Iterator for MappedRows<'stmt, F>
}
}
/// An iterator over the mapped resulting rows of a query, with an Error type
/// unifying with SqliteError.
pub struct AndThenRows<'stmt, F> {
rows: SqliteRows<'stmt>,
map: F,
}
impl<'stmt, T, E, F> Iterator for AndThenRows<'stmt, F>
where T: 'static,
E: convert::From<SqliteError>,
F: FnMut(SqliteRow) -> Result<T, E> {
type Item = Result<T, E>;
// Through the magic of FromIterator, if F returns a Result<T, E>,
// you can collect that to a Result<Vec<T>, E>
fn next(&mut self) -> Option<Self::Item> {
self.rows.next().map(|row_result| row_result
.map_err(E::from)
.and_then(|row| (self.map)(row)))
}
}
/// An iterator over the resulting rows of a query.
///
/// ## Warning
@ -920,6 +962,8 @@ mod test {
extern crate tempdir;
use super::*;
use self::tempdir::TempDir;
use std::error::Error as StdError;
use std::fmt;
// this function is never called, but is still type checked; in
// particular, calls with specific instantiations will require
@ -1081,6 +1125,184 @@ mod test {
assert_eq!(results.unwrap().concat(), "hello, world!");
}
#[test]
fn test_query_and_then() {
let db = checked_memory_handle();
let sql = "BEGIN;
CREATE TABLE foo(x INTEGER, y TEXT);
INSERT INTO foo VALUES(4, \"hello\");
INSERT INTO foo VALUES(3, \", \");
INSERT INTO foo VALUES(2, \"world\");
INSERT INTO foo VALUES(1, \"!\");
END;";
db.execute_batch(sql).unwrap();
let mut query = db.prepare("SELECT x, y FROM foo ORDER BY x DESC").unwrap();
let results: SqliteResult<Vec<String>> = query
.query_and_then(&[], |row| row.get_checked(1))
.unwrap()
.collect();
assert_eq!(results.unwrap().concat(), "hello, world!");
}
#[test]
fn test_query_and_then_fails() {
let db = checked_memory_handle();
let sql = "BEGIN;
CREATE TABLE foo(x INTEGER, y TEXT);
INSERT INTO foo VALUES(4, \"hello\");
INSERT INTO foo VALUES(3, \", \");
INSERT INTO foo VALUES(2, \"world\");
INSERT INTO foo VALUES(1, \"!\");
END;";
db.execute_batch(sql).unwrap();
let mut query = db.prepare("SELECT x, y FROM foo ORDER BY x DESC").unwrap();
let bad_type: SqliteResult<Vec<f64>> = query
.query_and_then(&[], |row| row.get_checked(1))
.unwrap()
.collect();
assert_eq!(bad_type, Err(SqliteError{
code: ffi::SQLITE_MISMATCH,
message: "Invalid column type".to_owned(),
}));
let bad_idx: SqliteResult<Vec<String>> = query
.query_and_then(&[], |row| row.get_checked(3))
.unwrap()
.collect();
assert_eq!(bad_idx, Err(SqliteError{
code: ffi::SQLITE_MISUSE,
message: "Invalid column index".to_owned(),
}));
}
#[test]
fn test_query_and_then_custom_error() {
#[derive(Debug)]
enum CustomError {
Sqlite(SqliteError),
};
impl fmt::Display for CustomError {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match *self {
CustomError::Sqlite(ref se) => write!(f, "{}: {}", self.description(), se),
}
}
}
impl StdError for CustomError {
fn description(&self) -> &str { "my custom error" }
fn cause(&self) -> Option<&StdError> {
match *self {
CustomError::Sqlite(ref se) => Some(se),
}
}
}
impl From<SqliteError> for CustomError {
fn from(se: SqliteError) -> CustomError {
CustomError::Sqlite(se)
}
}
type CustomResult<T> = Result<T, CustomError>;
let db = checked_memory_handle();
let sql = "BEGIN;
CREATE TABLE foo(x INTEGER, y TEXT);
INSERT INTO foo VALUES(4, \"hello\");
INSERT INTO foo VALUES(3, \", \");
INSERT INTO foo VALUES(2, \"world\");
INSERT INTO foo VALUES(1, \"!\");
END;";
db.execute_batch(sql).unwrap();
let mut query = db.prepare("SELECT x, y FROM foo ORDER BY x DESC").unwrap();
let results: CustomResult<Vec<String>> = query
.query_and_then(&[], |row| row.get_checked(1).map_err(CustomError::Sqlite))
.unwrap()
.collect();
assert_eq!(results.unwrap().concat(), "hello, world!");
}
#[test]
fn test_query_and_then_custom_error_fails() {
#[derive(Debug, PartialEq)]
enum CustomError {
SomeError,
Sqlite(SqliteError),
};
impl fmt::Display for CustomError {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match *self {
CustomError::SomeError => write!(f, "{}", self.description()),
CustomError::Sqlite(ref se) => write!(f, "{}: {}", self.description(), se),
}
}
}
impl StdError for CustomError {
fn description(&self) -> &str { "my custom error" }
fn cause(&self) -> Option<&StdError> {
match *self {
CustomError::SomeError => None,
CustomError::Sqlite(ref se) => Some(se),
}
}
}
impl From<SqliteError> for CustomError {
fn from(se: SqliteError) -> CustomError {
CustomError::Sqlite(se)
}
}
type CustomResult<T> = Result<T, CustomError>;
let db = checked_memory_handle();
let sql = "BEGIN;
CREATE TABLE foo(x INTEGER, y TEXT);
INSERT INTO foo VALUES(4, \"hello\");
INSERT INTO foo VALUES(3, \", \");
INSERT INTO foo VALUES(2, \"world\");
INSERT INTO foo VALUES(1, \"!\");
END;";
db.execute_batch(sql).unwrap();
let mut query = db.prepare("SELECT x, y FROM foo ORDER BY x DESC").unwrap();
let bad_type: CustomResult<Vec<f64>> = query
.query_and_then(&[], |row| row.get_checked(1).map_err(CustomError::Sqlite))
.unwrap()
.collect();
assert_eq!(bad_type, Err(CustomError::Sqlite(SqliteError{
code: ffi::SQLITE_MISMATCH,
message: "Invalid column type".to_owned(),
})));
let bad_idx: CustomResult<Vec<String>> = query
.query_and_then(&[], |row| row.get_checked(3).map_err(CustomError::Sqlite))
.unwrap()
.collect();
assert_eq!(bad_idx, Err(CustomError::Sqlite(SqliteError{
code: ffi::SQLITE_MISUSE,
message: "Invalid column index".to_owned(),
})));
let non_sqlite_err: CustomResult<Vec<String>> = query
.query_and_then(&[], |_| Err(CustomError::SomeError))
.unwrap()
.collect();
assert_eq!(non_sqlite_err, Err(CustomError::SomeError));
}
#[test]
fn test_query_row() {
let db = checked_memory_handle();