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Mark Statement::execute() and the fetch family [[nodiscard]] (#59) #60

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Mark Statement::execute() and the fetch family [[nodiscard]] (#59) #60

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6 changes: 6 additions & 0 deletions README.md
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Expand Up @@ -77,6 +77,12 @@ if (statement.execute(transaction))
transaction.commit();
```

Note that `execute()` already fetches a SELECT's first row — that is why the loop above is
`if (execute()) do ... while (fetchNext());` and not `execute(); while (fetchNext()) ...`,
which would silently skip the first row. `execute()` is marked `[[nodiscard]]` so the
compiler warns about the latter shape; cast to `void` to deliberately discard the result
(e.g. for DDL/DML, or when a row is known to exist).

## Using with vcpkg

This library is present in [firebird-vcpkg-registry](https://github.com/asfernandes/firebird-vcpkg-registry).
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18 changes: 18 additions & 0 deletions src/fb-cpp/Statement.h
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Expand Up @@ -309,9 +309,15 @@ namespace fbcpp

///
/// @brief Executes a prepared statement using the supplied transaction.
///
/// For a SELECT, this opens the cursor and already fetches the first row - a subsequent
/// `fetchNext()` positions on the second row. Cast to `void` to deliberately discard the
/// result (e.g. for DDL/DML, or when a row is known to exist).
///
/// @param transaction Transaction that will own the execution context.
/// @return `true` when execution yields a record.
///
[[nodiscard("execute() already fetches a SELECT's first row; looping on fetchNext() alone skips it")]]

@asfernandes asfernandes Jul 21, 2026

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As you see, this is not needed for DDL and I do not want that (void) thing everywhere.

bool execute(Transaction& transaction);

///
Expand All @@ -320,32 +326,44 @@ namespace fbcpp

///
/// @brief Fetches the next row in the current result set.
/// @return `true` when a row was fetched.
///
[[nodiscard("without checking the result, the cursor may be past the end")]]
bool fetchNext();

///
/// @brief Fetches the previous row in the current result set.
/// @return `true` when a row was fetched.
///
[[nodiscard("without checking the result, the cursor may be before the start")]]
bool fetchPrior();

///
/// @brief Positions the cursor on the first row.
/// @return `true` when a row was fetched.
///
[[nodiscard("without checking the result, the cursor position is unknown")]]
bool fetchFirst();

///
/// @brief Positions the cursor on the last row.
/// @return `true` when a row was fetched.
///
[[nodiscard("without checking the result, the cursor position is unknown")]]
bool fetchLast();

///
/// @brief Positions the cursor on the given absolute row number.
/// @return `true` when a row was fetched.
///
[[nodiscard("without checking the result, the cursor position is unknown")]]
bool fetchAbsolute(unsigned position);

///
/// @brief Moves the cursor by the requested relative offset.
/// @return `true` when a row was fetched.
///
[[nodiscard("without checking the result, the cursor position is unknown")]]
bool fetchRelative(int offset);

///
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14 changes: 7 additions & 7 deletions src/test/BackupManager.cpp
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Expand Up @@ -169,11 +169,11 @@ BOOST_DATA_TEST_CASE(backupAndRestoreRoundTrip, data::make(BACKUP_RESTORE_VERBOS

Statement create{
attachment, transaction, "create table test(id integer not null primary key, name varchar(20))"};
create.execute(transaction);
(void) create.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into test(id, name) values (1, 'backup')"};
insert.execute(transaction);
(void) insert.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -225,11 +225,11 @@ BOOST_AUTO_TEST_CASE(restoreReplace)
Transaction transaction{attachment};

Statement create{attachment, transaction, "create table test(id integer not null primary key)"};
create.execute(transaction);
(void) create.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into test(id) values (7)"};
insert.execute(transaction);
(void) insert.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -270,20 +270,20 @@ BOOST_AUTO_TEST_CASE(multiFileDatabaseAndBackupRoundTrip)

Statement create{
attachment, transaction, "create table test(id integer not null primary key, name varchar(50))"};
create.execute(transaction);
(void) create.execute(transaction);
transaction.commitRetaining();

Statement addFile{
attachment, transaction, "alter database add file '" + sourceSecondaryPath + "' starting at page 241"};
addFile.execute(transaction);
(void) addFile.execute(transaction);
transaction.commitRetaining();

for (int i = 1; i <= 200; ++i)
{
Statement insert{attachment, transaction, "insert into test(id, name) values (?, ?)"};
insert.setInt32(0, i);
insert.setString(1, "row-" + std::to_string(i) + std::string(40, 'x'));
insert.execute(transaction);
(void) insert.execute(transaction);
}
transaction.commitRetaining();

Expand Down
18 changes: 9 additions & 9 deletions src/test/Batch.cpp
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Expand Up @@ -45,7 +45,7 @@ BOOST_AUTO_TEST_CASE(constructorFromStatementAndExecute)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null, name varchar(50))"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -111,7 +111,7 @@ BOOST_AUTO_TEST_CASE(constructorFromAttachmentAndExecute)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null, val integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -184,7 +184,7 @@ BOOST_AUTO_TEST_CASE(moveConstructorTransfersOwnership)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -220,7 +220,7 @@ BOOST_AUTO_TEST_CASE(executeReportsNoInfoWhenRecordCountsDisabled)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -253,7 +253,7 @@ BOOST_AUTO_TEST_CASE(executeWithBadDataReportsExecuteFailed)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null primary key)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -312,7 +312,7 @@ BOOST_AUTO_TEST_CASE(cancelDiscardsMessages)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -352,7 +352,7 @@ BOOST_AUTO_TEST_CASE(blobWithIdEngine)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null, data blob)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -410,7 +410,7 @@ BOOST_AUTO_TEST_CASE(registerExistingBlob)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null, data blob)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

Expand Down Expand Up @@ -473,7 +473,7 @@ BOOST_AUTO_TEST_CASE(closeReleasesHandle)
{ // scope
Transaction transaction{attachment};
Statement ddl{attachment, transaction, "recreate table batch_test (id integer not null)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commit();
}

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2 changes: 1 addition & 1 deletion src/test/DatabaseManager.cpp
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Expand Up @@ -118,7 +118,7 @@ BOOST_AUTO_TEST_CASE(restoreWithReplicaMode)
CLIENT, sourceDatabaseUri, AttachmentOptions().setCreateDatabase(true).setConnectionCharSet("UTF8")};
Transaction transaction{attachment};
Statement create{attachment, transaction, "create table test(id integer)"};
create.execute(transaction);
(void) create.execute(transaction);
transaction.commit();
}

Expand Down
24 changes: 12 additions & 12 deletions src/test/RowSet.cpp
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Expand Up @@ -40,14 +40,14 @@ BOOST_AUTO_TEST_CASE(fetchRowsIntoRowSet)
Transaction transaction{attachment};

Statement ddl{attachment, transaction, "create table t (col integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into t (col) values (?)"};
for (int i = 1; i <= 5; ++i)
{
insert.setInt32(0, i);
insert.execute(transaction);
(void) insert.execute(transaction);
}

Statement select{attachment, transaction, "select col from t order by col"};
Expand Down Expand Up @@ -79,14 +79,14 @@ BOOST_AUTO_TEST_CASE(fetchFewerRowsThanMaxRows)
Transaction transaction{attachment};

Statement ddl{attachment, transaction, "create table t (col integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into t (col) values (?)"};
for (int i = 1; i <= 3; ++i)
{
insert.setInt32(0, i);
insert.execute(transaction);
(void) insert.execute(transaction);
}

Statement select{attachment, transaction, "select col from t order by col"};
Expand All @@ -110,14 +110,14 @@ BOOST_AUTO_TEST_CASE(rowSetIsDisconnectedFromStatement)
Transaction transaction{attachment};

Statement ddl{attachment, transaction, "create table t (col integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into t (col) values (?)"};
for (int i = 1; i <= 3; ++i)
{
insert.setInt32(0, i);
insert.execute(transaction);
(void) insert.execute(transaction);
}

Statement select{attachment, transaction, "select col from t order by col"};
Expand Down Expand Up @@ -147,14 +147,14 @@ BOOST_AUTO_TEST_CASE(moveConstructor)
Transaction transaction{attachment};

Statement ddl{attachment, transaction, "create table t (col integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into t (col) values (?)"};
for (int i = 1; i <= 3; ++i)
{
insert.setInt32(0, i);
insert.execute(transaction);
(void) insert.execute(transaction);
}

Statement select{attachment, transaction, "select col from t order by col"};
Expand Down Expand Up @@ -182,14 +182,14 @@ BOOST_AUTO_TEST_CASE(moveAssignment)
Transaction transaction{attachment};

Statement ddl{attachment, transaction, "create table t (col integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into t (col) values (?)"};
for (int i = 1; i <= 5; ++i)
{
insert.setInt32(0, i);
insert.execute(transaction);
(void) insert.execute(transaction);
}

Statement select{attachment, transaction, "select col from t order by col"};
Expand Down Expand Up @@ -223,14 +223,14 @@ BOOST_AUTO_TEST_CASE(fetchMultipleBatchesFromSameStatement)
Transaction transaction{attachment};

Statement ddl{attachment, transaction, "create table t (col integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into t (col) values (?)"};
for (int i = 1; i <= 10; ++i)
{
insert.setInt32(0, i);
insert.execute(transaction);
(void) insert.execute(transaction);
}

Statement select{attachment, transaction, "select col from t order by col"};
Expand Down
4 changes: 2 additions & 2 deletions src/test/ScrollableCursor.cpp
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Expand Up @@ -45,14 +45,14 @@ BOOST_AUTO_TEST_CASE(scrollableCursorSupportsFetchMethods)
Transaction transaction{attachment};

Statement ddl{attachment, transaction, "create table t (col integer)"};
ddl.execute(transaction);
(void) ddl.execute(transaction);
transaction.commitRetaining();

Statement insert{attachment, transaction, "insert into t (col) values (?)"};
for (int i = 1; i <= 5; ++i)
{
insert.setInt32(0, i);
insert.execute(transaction);
(void) insert.execute(transaction);
}

Statement select{attachment, transaction, "select col from t order by col",
Expand Down
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