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Avoid iterating joined columns on every row

This commit is contained in:
Simon Binder 2024-02-12 22:30:08 +01:00
parent 30f30ba313
commit 2d00149cb9
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GPG Key ID: 7891917E4147B8C0
1 changed files with 33 additions and 5 deletions
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38
drift/lib/src/runtime/query_builder/statements/select/select_with_join.dart
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@ -277,11 +277,32 @@ class JoinedSelectStatement<FirstT extends HasResultSet, FirstD>
});
}
/// Precomputes information used to parse results in [_mapWithStructure].
///
/// As the column names are the same for each row, we can pre-compute some
/// information (like the column aliases for [_LazyExpressionMap]) once and
/// then apply them to every row.
_ResultStructure _computeResultStructure() {
return _ResultStructure(
columnAliases: {
for (final (expr, alias) in _expandedColumns) expr: alias,
},
queriedTables: _queriedTables(true).toList(),
);
}
@override
Future<TypedResult> _mapRow(Map<String, Object?> row) async {
return await _mapWithStructure(_computeResultStructure(), row);
}
/// Reads a raw database [row] into a [TypedResult] by using information that
/// doesn't change between rows, such as the expected columns or tables.
Future<TypedResult> _mapWithStructure(
_ResultStructure structure, Map<String, Object?> row) async {
final readTables = <ResultSetImplementation, dynamic>{};
for (final table in _queriedTables(true)) {
for (final table in structure.queriedTables) {
final prefix = '${table.aliasedName}.';
// if all columns of this table are null, skip the table
if (table.$columns.any((c) => row[prefix + c.$name] != null)) {
@ -295,16 +316,16 @@ class JoinedSelectStatement<FirstT extends HasResultSet, FirstD>
readTables,
driftRow,
_LazyExpressionMap(
{
for (final (expr, alias) in _expandedColumns) expr: alias,
},
structure.columnAliases,
driftRow,
),
);
}
Future<List<TypedResult>> _mapResponse(List<Map<String, Object?>> rows) {
return Future.wait(rows.map(_mapRow));
final structure = _computeResultStructure();
return Future.wait(rows.map((row) => _mapWithStructure(structure, row)));
}
Never _warnAboutDuplicate(
@ -356,3 +377,10 @@ class _LazyExpressionMap extends UnmodifiableMapBase<Expression, Object?> {
@override
bool containsKey(Object? key) => _columnAliases.containsKey(key);
}
class _ResultStructure {
final Map<Expression, String> columnAliases;
final List<ResultSetImplementation> queriedTables;
_ResultStructure({required this.columnAliases, required this.queriedTables});
}