QSqlQueryModel with Open Cypher query issue

Alex Mirgorodskiy

Hi all!
I implemented simple model-view program which work with AgensGraph (fork of the PostgreSQL) base .
View part work on QML code. Model implemented on C++.
It is class inherited from QSqlQueryModel . Code was written by Qt Docs Example with one difference - query use OpenCypher instead SQL.
It's pretty well work with Qt 5.5.1 but not work with Qt 5.11.2

code for query:

 const char* ProjectBaseModel::SQL_SELECT =
"SET graph_path = prod; "
" match (n:task) return properties(n) AS n, n.task_type as t ;";

Application connectedto the base but query not executed. It seems like empty query.
As you can see below it implemented in a refresh() method

void ProjectBaseModel::refresh()
{
    this->setQuery(SQL_SELECT);
}

The OpenCypher code is work in console connected with base and even in the Pgadmin.
Result of the query is:

n                           |  t
----------------------------+-------------
{"task_type": "Modeling"}   | "Modeling"
{"task_type": "Texturing"}  | "Texturing"
{"task_type": "Rig"}        | "Rig"
{"task_type": "Shading"}    | "Shading"

I want to note also : the application work if I use SQL query to the tables from my base.
Have somebody same issues?

Thanks,
Alex

SGaist

Hi and welcome to devnet,

Did you check if you get any errors from the query and it's execution ?

Alex Mirgorodskiy

Hi SGaist.
My application don't generate any errors.
I had insert qDebug() calls for catch some states of some elements of the program
When I am compile it in the Qt5.5.1 application work and show my ListView with model data. I attached pic bellow.

And application output is:

--Data Base Info after connection------------------------
db.tables() =  ("testTable", "world", "projects", "prod.ag_edge", "prod.ag_vertex", "prod.task", "prod.dependency", "pg_catalog.ag_graph", "pg_catalog.ag_label")
db.databaseName() =  "atmosphere_db"
db.connectionName() =  "qt_sql_default_connection"
db.driverName() =  "QPSQL"
--End Data Base Info ------------------------- 

--- Start roleNames() ---------
------------
roleName idx =  0 "n"
------------
roleName idx =  1 "t"
--- End roleNames() ---------
this->roleNames() =  QHash((258, "t")(257, "n"))
this->rowCount() =  4
QueryText =  SET graph_path = prod;  match (n:task) return properties(n) AS n, n.task_type as t ;
query.lastError() =  QSqlError("", "", "")
this->rowCount() =  4
--- Start roleNames() ---------
------------
roleName idx =  0 "n"
------------
roleName idx =  1 "t"
--- End roleNames() ---------
QModelIndex modelIndex =  QModelIndex(0,0,0x0,ProjectBaseModel(0x7fff3a984130))
QModelIndex modelIndex =  QModelIndex(0,1,0x0,ProjectBaseModel(0x7fff3a984130))
QModelIndex modelIndex =  QModelIndex(1,0,0x0,ProjectBaseModel(0x7fff3a984130))
QModelIndex modelIndex =  QModelIndex(1,1,0x0,ProjectBaseModel(0x7fff3a984130))
QModelIndex modelIndex =  QModelIndex(2,0,0x0,ProjectBaseModel(0x7fff3a984130))
QModelIndex modelIndex =  QModelIndex(2,1,0x0,ProjectBaseModel(0x7fff3a984130))
QModelIndex modelIndex =  QModelIndex(3,0,0x0,ProjectBaseModel(0x7fff3a984130))
QModelIndex modelIndex =  QModelIndex(3,1,0x0,ProjectBaseModel(0x7fff3a984130))

When I compile the application in the Qt5.11.2 output is:

--Data Base Info after connection------------------------
db.tables() =  ("testTable", "world", "projects", "prod.ag_edge", "prod.ag_vertex", "prod.task", "prod.dependency", "pg_catalog.ag_graph", "pg_catalog.ag_label")
db.databaseName() =  "atmosphere_db"
db.connectionName() =  "qt_sql_default_connection"
db.driverName() =  "QPSQL"
--End Data Base Info ------------------------- 

--- Start roleNames() ---------
------------
roleName idx =  0 "n"
------------
roleName idx =  1 "t"
--- End roleNames() ---------
this->roleNames() =  QHash((257, "n")(258, "t"))
this->rowCount() =  0
QueryText =  SET graph_path = prod;  match (n:task) return properties(n) AS n, n.task_type as t ;
query.lastError() =  QSqlError("", "", "")
this->rowCount() =  0

Alex

SGaist

Would it be possible for you to provide a minimal compilable example that creates a dummy database to reproduce this behaviour ?

Alex Mirgorodskiy

@SGaist Are you mean exapmle of OpenCypher commands for creating database or my Qt code for reading from base? I can share both.

Alex Mirgorodskiy

This is my OpenSypher code for creation the graph:

atmosphere_db=# CREATE GRAPH prod;
CREATE GRAPH
atmosphere_db=# 
SET graph_path = prod;
CREATE VLABEL task;
CREATE ELABEL dependency;
CREATE (:task {task_type: 'Modeling'})-[:dependency {dep_type:'FS'}]->(:task {task_type: 'Texturing'});
CREATE (:task {task_type: 'Rig'})-[:dependency {dep_type:'FS'}]->(:task {task_type: 'Shading'});

SGaist

@Alex-Mirgorodskiy said in QSqlQueryModel with Open Cypher query issue:

@SGaist Are you mean exapmle of OpenCypher commands for creating database or my Qt code for reading from base? I can share both.

I meant a minimal application that would create the DB and do the access that are now failing.

Alex Mirgorodskiy

@SGaist Hi. But I created the base from console in Agens app (like psql). It was my first testing of Qt with Agens graph.
I wrote simplest code for catching the source of issue. But not found something yet. It work in the Qt5.5 and nor work in the Qt5.11.2

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QSqlDatabase db = QSqlDatabase::addDatabase("QPSQL");
    //QSqlDatabase db = QSqlDatabase::database();
    db.setDatabaseName("atmosphere_db");
    db.setUserName("atmosphere_user");
    db.setHostName("localhost");
    db.setPassword("atmosphere");
    if (!db.open()) {
        qDebug() << "Cannot open database:";
        return 1;
    }

    qDebug() << "--Data Base Info after connection--------------";
    qDebug() << "db.tables() = " << db.tables();
    qDebug() << "db.databaseName() = " << db.databaseName();
    qDebug() << "db.connectionName() = " << db.connectionName();
    qDebug() << "db.driverName() = " << db.driverName();
    qDebug() << "--End Data Base Info -------------------------" << "\n";

    QSqlQuery q(db);
    qDebug() << q.lastError();
   
   q.exec("SET graph_path = prod; match (n:task) return properties(n) AS n, n.task_type as t ;");
   
   qDebug() << q.lastError();

    while (q.next()) {
            qDebug() <<  q.value(0).toString() << "|" << q.value(1).toString() ;

        }

    return a.exec();
}

Alex Mirgorodskiy

Finally I solved this issue. The queries pretty works if it do through separate "exec" calls. I wrote an example below

query = QSqlQuery(db);
query.exec("SET graph_path = some_graph; ");
query.exec("MATCH some OpenCypher match RETURN some Match variable;");

SGaist

Sorry, I lost track on this one.

Glad you found out and thanks for sharing !

Since you have it working now, please mark the thread as solved using the "Topic Tools" button so that other forum users may know a solution has been found :)