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Change how Aggregate works when called on no rows.

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Before this commit, if the aggregate function was called on 0 rows, it
would always return NULL (and never call Aggregate::init() or
finalize()). Now, init() and finalize() are always called to get the
result of the function, even if step() is never called.
This commit is contained in:
John Gallagher 2016-01-07 12:33:32 -05:00
parent e4819b6adc
commit b189f6ba66
1 changed files with 83 additions and 38 deletions
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121
src/functions.rs
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@ -155,14 +155,6 @@ impl ToResult for Null {
}
}
// sqlite3_result_error_code, c_int
// sqlite3_result_error_nomem
// sqlite3_result_error_toobig
// sqlite3_result_error, *const c_char, c_int
// sqlite3_result_zeroblob
// sqlite3_result_value
/// A trait for types that can be created from a SQLite function parameter value.
pub trait FromValue: Sized {
unsafe fn parameter_value(v: *mut sqlite3_value) -> Result<Self>;
@ -337,15 +329,19 @@ impl<'a> Context<'a> {
/// `A` is the type of the aggregation context and `T` is the type of the final result.
/// Implementations should be stateless.
pub trait Aggregate<A, T> where T: ToResult {
/// Initializes the aggregation context.
/// Initializes the aggregation context. Will be called exactly once for each
/// invocation of the function.
fn init(&self) -> A;
/// "step" function called once for each row in an aggregate group.
/// "step" function called once for each row in an aggregate group. May be called
/// 0 times if there are no rows.
fn step(&self, &mut Context, &mut A) -> Result<()>;
/// Computes and returns the final result.
/// Computes and returns the final result. Will be called exactly once for each
/// invocation of the function.
fn finalize(&self, A) -> Result<T>;
}
impl Connection {
/// Attach a user-defined scalar function to this database connection.
///
@ -489,9 +485,26 @@ impl InnerConnection {
where D: Aggregate<A, T>,
T: ToResult
{
unsafe extern "C" fn call_boxed_closure<A, D, T>(ctx: *mut sqlite3_context,
argc: c_int,
argv: *mut *mut sqlite3_value)
// Get our aggregation context from the sqlite3_context.
unsafe fn aggregate_context<A, D, T>(agg: &D, ctx: *mut sqlite3_context) -> Result<*mut A>
where D: Aggregate<A, T>,
T: ToResult
{
let pac = ffi::sqlite3_aggregate_context(ctx, ::std::mem::size_of::<*mut A>() as c_int)
as *mut *mut A;
if pac.is_null() {
return Err(Error::SqliteFailure(ffi::Error::new(ffi::SQLITE_NOMEM), None));
}
if (*pac).is_null() {
let a = agg.init();
*pac = Box::into_raw(Box::new(a));
}
Ok(*pac)
}
unsafe extern "C" fn call_boxed_step<A, D, T>(ctx: *mut sqlite3_context,
argc: c_int,
argv: *mut *mut sqlite3_value)
where D: Aggregate<A, T>,
T: ToResult
{
@ -499,18 +512,12 @@ impl InnerConnection {
assert!(!boxed_aggr.is_null(),
"Internal error - null aggregate pointer");
// TODO Validate: double indirection: `pac` allocated/freed by SQLite and `ac` allocated/freed by Rust.
let pac = ffi::sqlite3_aggregate_context(ctx, ::std::mem::size_of::<*mut A>() as c_int) as *mut *mut A;
if pac.is_null() {
ffi::sqlite3_result_error_nomem(ctx);
return;
}
let ac: *mut A = if (*pac).is_null() {
let a = (*boxed_aggr).init();
*pac = Box::into_raw(Box::new(a));
*pac
} else {
*pac
let agg_ctx = match aggregate_context(&*boxed_aggr, ctx) {
Ok(agg_ctx) => agg_ctx,
Err(_) => {
ffi::sqlite3_result_error_nomem(ctx);
return;
}
};
let mut ctx = Context {
@ -518,7 +525,7 @@ impl InnerConnection {
args: slice::from_raw_parts(argv, argc as usize),
};
match (*boxed_aggr).step(&mut ctx, &mut *ac) {
match (*boxed_aggr).step(&mut ctx, &mut *agg_ctx) {
Ok(_) => {}
Err(Error::SqliteFailure(err, s)) => {
ffi::sqlite3_result_error_code(ctx.ctx, err.extended_code);
@ -534,6 +541,7 @@ impl InnerConnection {
}
};
}
unsafe extern "C" fn call_boxed_final<A, D, T>(ctx: *mut sqlite3_context)
where D: Aggregate<A, T>,
T: ToResult
@ -542,12 +550,15 @@ impl InnerConnection {
assert!(!boxed_aggr.is_null(),
"Internal error - null aggregate pointer");
let pac = ffi::sqlite3_aggregate_context(ctx, 0) as *mut *mut A;
if pac.is_null() || (*pac).is_null() {
return;
}
let ac: *mut A = *pac;
let a = Box::from_raw(mem::transmute(ac)); // to be freed
let agg_ctx = match aggregate_context(&*boxed_aggr, ctx) {
Ok(agg_ctx) => agg_ctx,
Err(_) => {
ffi::sqlite3_result_error_nomem(ctx);
return;
}
};
let a = Box::from_raw(agg_ctx); // to be freed
match (*boxed_aggr).finalize(*a) {
Ok(r) => r.set_result(ctx),
@ -579,7 +590,7 @@ impl InnerConnection {
flags,
mem::transmute(boxed_aggr),
None,
Some(call_boxed_closure::<A, D, T>),
Some(call_boxed_step::<A, D, T>),
Some(call_boxed_final::<A, D, T>),
Some(mem::transmute(free_boxed_value::<D>)))
};
@ -772,14 +783,30 @@ mod test {
}
struct Sum;
struct Count;
impl Aggregate<i64, i64> for Sum {
impl Aggregate<Option<i64>, Option<i64>> for Sum {
fn init(&self) -> Option<i64> {
None
}
fn step(&self, ctx: &mut Context, sum: &mut Option<i64>) -> Result<()> {
*sum = Some(sum.unwrap_or(0) + try!(ctx.get::<i64>(0)));
Ok(())
}
fn finalize(&self, sum: Option<i64>) -> Result<Option<i64>> {
Ok(sum)
}
}
impl Aggregate<i64, i64> for Count {
fn init(&self) -> i64 {
0
}
fn step(&self, ctx: &mut Context, sum: &mut i64) -> Result<()> {
*sum = *sum + try!(ctx.get::<i64>(0));
fn step(&self, _ctx: &mut Context, sum: &mut i64) -> Result<()> {
*sum += 1;
Ok(())
}
@ -792,6 +819,8 @@ mod test {
fn test_sum() {
let db = Connection::open_in_memory().unwrap();
db.create_aggregate_function("my_sum", 1, true, Sum).unwrap();
// sum should return NULL when given no columns (contrast with count below)
let no_result = "SELECT my_sum(i) FROM (SELECT 2 AS i WHERE 1 <> 1)";
let result: Option<i64> = db.query_row(no_result, &[], |r| r.get(0))
.unwrap();
@ -808,4 +837,20 @@ mod test {
.unwrap();
assert_eq!((4, 2), result);
}
#[test]
fn test_count() {
let db = Connection::open_in_memory().unwrap();
db.create_aggregate_function("my_count", -1, true, Count).unwrap();
// count should return 0 when given no columns (contrast with sum above)
let no_result = "SELECT my_count(i) FROM (SELECT 2 AS i WHERE 1 <> 1)";
let result: i64 = db.query_row(no_result, &[], |r| r.get(0)).unwrap();
assert_eq!(result, 0);
let single_sum = "SELECT my_count(i) FROM (SELECT 2 AS i UNION ALL SELECT 2)";
let result: i64 = db.query_row(single_sum, &[], |r| r.get(0))
.unwrap();
assert_eq!(2, result);
}
}