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Modify Rows::next to tie its lifetime to the returned Row.

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This means Rows no longer implements Iterator, but it is no longer
possible to misuse it by accessing a stale Row handle.
This commit is contained in:
John Gallagher
2016-05-18 11:33:58 -05:00
parent e695ed8f03
commit 30733a3688
4 changed files with 64 additions and 135 deletions
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162
src/lib.rs
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@@ -63,12 +63,12 @@ extern crate lazy_static;
use std::default::Default;
use std::convert;
use std::marker::PhantomData;
use std::mem;
use std::ptr;
use std::fmt;
use std::path::{Path, PathBuf};
use std::rc::Rc;
use std::cell::{RefCell, Cell};
use std::cell::RefCell;
use std::ffi::{CStr, CString};
use std::result;
use std::str;
@@ -800,7 +800,11 @@ impl<'conn> Statement<'conn> {
}
}
/// Execute the prepared statement, returning an iterator over the resulting rows.
/// Execute the prepared statement, returning a handle to the resulting rows.
///
/// Due to lifetime restricts, the rows handle returned by `query` does not
/// implement the `Iterator` trait. Consider using `query_map` or `query_and_then`
/// instead, which do.
///
/// ## Example
///
@@ -811,7 +815,7 @@ impl<'conn> Statement<'conn> {
/// let mut rows = try!(stmt.query(&[]));
///
/// let mut names = Vec::new();
/// for result_row in rows {
/// while let Some(result_row) = rows.next() {
/// let row = try!(result_row);
/// names.push(row.get(0));
/// }
@@ -831,11 +835,8 @@ impl<'conn> Statement<'conn> {
Ok(Rows::new(self))
}
/// Executes the prepared statement and maps a function over the resulting
/// rows.
///
/// Unlike the iterator produced by `query`, the returned iterator does not expose the possibility
/// for accessing stale rows.
/// Executes the prepared statement and maps a function over the resulting rows, returning
/// an iterator over the mapped function results.
///
/// # Failure
///
@@ -855,9 +856,6 @@ impl<'conn> Statement<'conn> {
/// rows, where the function returns a `Result` with `Error` type implementing
/// `std::convert::From<Error>` (so errors can be unified).
///
/// Unlike the iterator produced by `query`, the returned iterator does not expose the possibility
/// for accessing stale rows.
///
/// # Failure
///
/// Will return `Err` if binding parameters fails.
@@ -941,7 +939,8 @@ impl<'stmt, T, F> Iterator for MappedRows<'stmt, F>
type Item = Result<T>;
fn next(&mut self) -> Option<Result<T>> {
self.rows.next().map(|row_result| row_result.map(|row| (self.map)(&row)))
let map = &mut self.map;
self.rows.next().map(|row_result| row_result.map(|row| (map)(&row)))
}
}
@@ -959,9 +958,10 @@ impl<'stmt, T, E, F> Iterator for AndThenRows<'stmt, F>
type Item = result::Result<T, E>;
fn next(&mut self) -> Option<Self::Item> {
let map = &mut self.map;
self.rows.next().map(|row_result| {
row_result.map_err(E::from)
.and_then(|row| (self.map)(&row))
.and_then(|row| (map)(&row))
})
}
}
@@ -969,52 +969,19 @@ impl<'stmt, T, E, F> Iterator for AndThenRows<'stmt, F>
/// Old name for `Rows`. `SqliteRows` is deprecated.
pub type SqliteRows<'stmt> = Rows<'stmt>;
/// An iterator over the resulting rows of a query.
///
/// ## Warning
///
/// Strongly consider using `query_map` or `query_and_then` instead of `query`; the former do not
/// suffer from the following problem.
///
/// Due to the way SQLite returns result rows of a query, it is not safe to attempt to get values
/// from a row after it has become stale (i.e., `next()` has been called again on the `Rows`
/// iterator). For example:
///
/// ```rust,no_run
/// # use rusqlite::{Connection, Result};
/// fn bad_function_will_panic(conn: &Connection) -> Result<i64> {
/// let mut stmt = try!(conn.prepare("SELECT id FROM my_table"));
/// let mut rows = try!(stmt.query(&[]));
///
/// let row0 = try!(rows.next().unwrap());
/// // row 0 is valid for now...
///
/// let row1 = try!(rows.next().unwrap());
/// // row 0 is now STALE, and row 1 is valid
///
/// let my_id = row0.get(0); // WILL PANIC because row 0 is stale
/// Ok(my_id)
/// }
/// ```
///
/// Please note that this means some of the methods on `Iterator` are not useful, such as `collect`
/// (which would result in a collection of rows, only the last of which can safely be used) and
/// `min`/`max` (which could return a stale row unless the last row happened to be the min or max,
/// respectively).
/// An handle for the resulting rows of a query.
pub struct Rows<'stmt> {
stmt: Option<&'stmt Statement<'stmt>>,
current_row: Rc<Cell<c_int>>,
}
impl<'stmt> Rows<'stmt> {
fn new(stmt: &'stmt Statement<'stmt>) -> Rows<'stmt> {
Rows {
stmt: Some(stmt),
current_row: Rc::new(Cell::new(0)),
}
}
fn get_expected_row(&mut self) -> Result<Row<'stmt>> {
fn get_expected_row<'a>(&'a mut self) -> Result<Row<'a, 'stmt>> {
match self.next() {
Some(row) => row,
None => Err(Error::QueryReturnedNoRows),
@@ -1028,21 +995,24 @@ impl<'stmt> Rows<'stmt> {
}
}
}
}
impl<'stmt> Iterator for Rows<'stmt> {
type Item = Result<Row<'stmt>>;
fn next(&mut self) -> Option<Result<Row<'stmt>>> {
/// Attempt to get the next row from the query. Returns `Some(Ok(Row))` if there
/// is another row, `Some(Err(...))` if there was an error getting the next
/// row, and `None` if all rows have been retrieved.
///
/// ## Note
///
/// This interface is not compatible with Rust's `Iterator` trait, because the
/// lifetime of the returned row is tied to the lifetime of `self`. This is a
/// "streaming iterator". For a more natural interface, consider using `query_map`
/// or `query_and_then` instead, which return types that implement `Iterator`.
pub fn next<'a>(&'a mut self) -> Option<Result<Row<'a, 'stmt>>> {
self.stmt.and_then(|stmt| {
match unsafe { ffi::sqlite3_step(stmt.stmt) } {
ffi::SQLITE_ROW => {
let current_row = self.current_row.get() + 1;
self.current_row.set(current_row);
Some(Ok(Row {
stmt: stmt,
current_row: self.current_row.clone(),
row_idx: current_row,
phantom: PhantomData,
}))
}
ffi::SQLITE_DONE => {
@@ -1065,46 +1035,22 @@ impl<'stmt> Drop for Rows<'stmt> {
}
/// Old name for `Row`. `SqliteRow` is deprecated.
pub type SqliteRow<'stmt> = Row<'stmt>;
pub type SqliteRow<'a, 'stmt> = Row<'a, 'stmt>;
/// A single result row of a query.
pub struct Row<'stmt> {
pub struct Row<'a, 'stmt> {
stmt: &'stmt Statement<'stmt>,
current_row: Rc<Cell<c_int>>,
row_idx: c_int,
phantom: PhantomData<&'a ()>,
}
impl<'stmt> Row<'stmt> {
impl<'a, 'stmt> Row<'a, 'stmt> {
/// Get the value of a particular column of the result row.
///
/// Note that `Row` can panic at runtime if you use it incorrectly. When you are
/// retrieving the rows of a query, a row becomes stale once you have requested the next row,
/// and the values can no longer be retrieved. In general (when using looping over the rows,
/// for example) this isn't an issue, but it means you cannot do something like this:
///
/// ```rust,no_run
/// # use rusqlite::{Connection, Result};
/// fn bad_function_will_panic(conn: &Connection) -> Result<i64> {
/// let mut stmt = try!(conn.prepare("SELECT id FROM my_table"));
/// let mut rows = try!(stmt.query(&[]));
///
/// let row0 = try!(rows.next().unwrap());
/// // row 0 is value now...
///
/// let row1 = try!(rows.next().unwrap());
/// // row 0 is now STALE, and row 1 is valid
///
/// let my_id = row0.get(0); // WILL PANIC because row 0 is stale
/// Ok(my_id)
/// }
/// ```
///
/// ## Failure
///
/// Panics if the underlying SQLite column type is not a valid type as a source for `T`.
///
/// Panics if `idx` is outside the range of columns in the returned query or if this row
/// is stale.
/// Panics if `idx` is outside the range of columns in the returned query.
pub fn get<I: RowIndex, T: FromSql>(&self, idx: I) -> T {
self.get_checked(idx).unwrap()
}
@@ -1121,12 +1067,7 @@ impl<'stmt> Row<'stmt> {
///
/// Returns an `Error::InvalidColumnName` if `idx` is not a valid column name
/// for this row.
///
/// Returns an `Error::GetFromStaleRow` if this row is stale.
pub fn get_checked<I: RowIndex, T: FromSql>(&self, idx: I) -> Result<T> {
if self.row_idx != self.current_row.get() {
return Err(Error::GetFromStaleRow);
}
unsafe {
let idx = try!(idx.idx(self.stmt));
@@ -1317,15 +1258,24 @@ mod test {
let mut query = db.prepare("SELECT x FROM foo WHERE x < ? ORDER BY x DESC").unwrap();
{
let rows = query.query(&[&4i32]).unwrap();
let v: Vec<i32> = rows.map(|r| r.unwrap().get(0)).collect();
let mut rows = query.query(&[&4i32]).unwrap();
let mut v = Vec::<i32>::new();
while let Some(row) = rows.next() {
v.push(row.unwrap().get(0));
}
assert_eq!(v, [3i32, 2, 1]);
}
{
let rows = query.query(&[&3i32]).unwrap();
let v: Vec<i32> = rows.map(|r| r.unwrap().get(0)).collect();
let mut rows = query.query(&[&3i32]).unwrap();
let mut v = Vec::<i32>::new();
while let Some(row) = rows.next() {
v.push(row.unwrap().get(0));
}
assert_eq!(v, [2i32, 1]);
}
}
@@ -1388,26 +1338,6 @@ mod test {
assert!(format!("{}", err).contains("does_not_exist"));
}
#[test]
fn test_row_expiration() {
let db = checked_memory_handle();
db.execute_batch("CREATE TABLE foo(x INTEGER)").unwrap();
db.execute_batch("INSERT INTO foo(x) VALUES(1)").unwrap();
db.execute_batch("INSERT INTO foo(x) VALUES(2)").unwrap();
let mut stmt = db.prepare("SELECT x FROM foo ORDER BY x").unwrap();
let mut rows = stmt.query(&[]).unwrap();
let first = rows.next().unwrap().unwrap();
let second = rows.next().unwrap().unwrap();
assert_eq!(2i32, second.get(0));
match first.get_checked::<i32, i32>(0).unwrap_err() {
Error::GetFromStaleRow => (),
err => panic!("Unexpected error {}", err),
}
}
#[test]
fn test_last_insert_rowid() {
let db = checked_memory_handle();