QPSQL: Add support for multiple result sets

This change adds support for multiple result sets in PostgreSQL.

[Important Behavior Changes] The QPSQL driver now supports multiple
result sets. Since QPSQL previously did not support multiple result
sets, there may be some compatibility issues with the existing code
that executed several queries as one and were expecting to get
the results of the last one. In this case use QSqlQuery::nextResult()
to move to the last result set.

[ChangeLog][QtSql][QPSQL] Added support for multiple result sets

Change-Id: I2bfc91f512c4dac83116f3aa42833839a6da084c
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

1 files changed, 48 insertions, 1 deletions

diff --git a/src/plugins/sqldrivers/psql/qsql_psql.cpp b/src/plugins/sqldrivers/psql/qsql_psql.cpp
index 6de7797c19..dfca183ff0 100644
--- a/src/plugins/sqldrivers/psql/qsql_psql.cpp
+++ b/src/plugins/sqldrivers/psql/qsql_psql.cpp
@@ -152,6 +152,7 @@ protected:
     bool fetchFirst() override;
     bool fetchLast() override;
     bool fetchNext() override;
+    bool nextResult() override;
     QVariant data(int i) override;
     bool isNull(int field) override;
     bool reset (const QString &query) override;
@@ -325,6 +326,7 @@ public:
     void deallocatePreparedStmt();
 
     PGresult *result;
+    QList<PGresult*> nextResultSets;
     int currentSize;
     bool canFetchMoreRows;
     StatementId stmtId;
@@ -479,6 +481,8 @@ void QPSQLResult::cleanup()
     if (d->result)
         PQclear(d->result);
     d->result = nullptr;
+    while (!d->nextResultSets.isEmpty())
+        PQclear(d->nextResultSets.takeFirst());
     if (d->stmtId != InvalidStatementId)
         d->drv_d_func()->finishQuery(d->stmtId);
     d->stmtId = InvalidStatementId;
@@ -608,6 +612,39 @@ bool QPSQLResult::fetchNext()
     return true;
 }
 
+bool QPSQLResult::nextResult()
+{
+    Q_D(QPSQLResult);
+    if (!isActive())
+        return false;
+
+    setAt(QSql::BeforeFirstRow);
+
+    if (isForwardOnly()) {
+        if (d->canFetchMoreRows) {
+            // Skip all rows from current result set
+            while (d->result && PQresultStatus(d->result) == PGRES_SINGLE_TUPLE) {
+                PQclear(d->result);
+                d->result = d->drv_d_func()->getResult(d->stmtId);
+            }
+            d->canFetchMoreRows = false;
+            // Check for unexpected errors
+            if (d->result && PQresultStatus(d->result) == PGRES_FATAL_ERROR)
+                return d->processResults();
+        }
+        // Fetch first result from next result set
+        if (d->result)
+            PQclear(d->result);
+        d->result = d->drv_d_func()->getResult(d->stmtId);
+        return d->processResults();
+    }
+
+    if (d->result)
+        PQclear(d->result);
+    d->result = d->nextResultSets.isEmpty() ? nullptr : d->nextResultSets.takeFirst();
+    return d->processResults();
+}
+
 QVariant QPSQLResult::data(int i)
 {
     Q_D(const QPSQLResult);
@@ -729,6 +766,11 @@ bool QPSQLResult::reset (const QString& query)
         setForwardOnly(d->drv_d_func()->setSingleRowMode());
 
     d->result = d->drv_d_func()->getResult(d->stmtId);
+    if (!isForwardOnly()) {
+        // Fetch all result sets right away
+        while (PGresult *nextResultSet = d->drv_d_func()->getResult(d->stmtId))
+            d->nextResultSets.append(nextResultSet);
+    }
     return d->processResults();
 }
 
@@ -914,6 +956,11 @@ bool QPSQLResult::exec()
         setForwardOnly(d->drv_d_func()->setSingleRowMode());
 
     d->result = d->drv_d_func()->getResult(d->stmtId);
+    if (!isForwardOnly()) {
+        // Fetch all result sets right away
+        while (PGresult *nextResultSet = d->drv_d_func()->getResult(d->stmtId))
+            d->nextResultSets.append(nextResultSet);
+    }
     return d->processResults();
 }
 
@@ -1132,6 +1179,7 @@ bool QPSQLDriver::hasFeature(DriverFeature f) const
     case LastInsertId:
     case LowPrecisionNumbers:
     case EventNotifications:
+    case MultipleResultSets:
     case BLOB:
         return true;
     case PreparedQueries:
@@ -1141,7 +1189,6 @@ bool QPSQLDriver::hasFeature(DriverFeature f) const
     case NamedPlaceholders:
     case SimpleLocking:
     case FinishQuery:
-    case MultipleResultSets:
     case CancelQuery:
         return false;
     case Unicode: