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Thread: MySQL INSERT query fails in Qt

  1. #1
    Join Date
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    Default MySQL INSERT query fails in Qt

    Hello.

    I am writing some code in Qt 4.8 using Qt's MySQL driver for accessing a database for adding or updating some entries on a table. The UPDATE query is working fine but the INSERT query fails without giving any error message (i.e. db.lastError().databaseText() and db.lastError().driverText() are empty strings indicating an undefined error number (-1)).

    After spending several hours I am still unable to detect the problem. Rearranging the INSERT query in a single line or multiple lines doesn't seem to have any effect. Below I have included the definition of the table's entries and a part of the code performing the INSERT and UPDATE query. I hope someone can spot the problem. Thanks!

    Here is the structure of the table:

    MySQL Table Name:
    Qt Code:
    1. teeth
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    MySQL Table columns:
    Qt Code:
    1. [int(11)]idteeth,
    2. [int(11)]patients_idpatient,
    3. [int(11)]location,
    4. [float]screw_start_x,
    5. [float]screw_start_y,
    6. [float]screw_start_z,
    7. [float]screw_end_x,
    8. [float]screw_end_y,
    9. [float]screw_end_z,
    10. [float]center_x,
    11. [float]center_y,
    12. [float]center_z,
    13. [int(11)]screws_idscrews,
    14. [mediumblob]screwPolyTransform,
    15. [int(1)]isEditedByDentist,
    16. [int(1)]isCustomImplant
    To copy to clipboard, switch view to plain text mode 

    And here is the part of the code performing the UPDATE and INSERT queries

    Qt Code:
    1. //database driver set to MySQL
    2. QSqlDatabase db = QSqlDatabase::addDatabase("QMYSQL");
    3.  
    4. QSqlQuery query;
    5.  
    6. //SQL Server details.
    7. db.setHostName(_TARGET_SERVER_SQL_HOST_);
    8. db.setPort(QString(_TARGET_SERVER_SQL_PORT_).toInt());
    9. db.setDatabaseName(_TARGET_SERVER_SQL_DB_);
    10. db.setUserName(_TARGET_SERVER_SQL_USER_);
    11. db.setPassword(_TARGET_SERVER_SQL_PASS_);
    12.  
    13.  
    14. if(db.open())
    15. {
    16. //db opened successfully
    17.  
    18. teeth_count = currentPatientRecord->getImplantsCount();
    19.  
    20. //repeat the UPDATE query for all the patient's implants and while there is no error
    21. while(i < teeth_count && isQuerySuccess)
    22. {
    23. current_tooth = currentPatientRecord->getTeethList()->at(i);
    24.  
    25. //update only the records of implants with complete specifications
    26. if(current_tooth->isScrewTypeSet())
    27. {
    28. //if the implant has no record in the database then create one by issuing an INSERT query
    29. //otherwise simply update the existing record
    30. if(!current_tooth->getHasDatabaseRecord())
    31. {
    32. query.prepare("INSERT INTO teeth "
    33. "(patients_idpatient, location, screw_start_x, screw_start_y, screw_start_z, "
    34. "screw_end_x, screw_end_y, screw_end_z, center_x, center_y, center_z, "
    35. "screws_idscrews, screwPolyTransform, isEditedByDentist, isCustomImplant) "
    36. "VALUES (:id_patient, :dentist_location_id, :screwSx, :screwSy, :screwSz, "
    37. ":screwEx, :screwEy, :screwEz, :screwCx, :screwCy, :screwCz, :screw_type_id, "
    38. ":screwPolyTransformStream, :is_edited_by_dentist, :is_custom)");
    39.  
    40. //bind values which are exclusive to the INSERT query
    41. query.bindValue(":dentist_location_id",(int)current_tooth->getLocationID());
    42. }
    43. else
    44. {
    45. query.prepare("UPDATE teeth SET screw_start_x=:screwSx, screw_start_y=:screwSy, screw_start_z=:screwSz, "
    46. "screw_end_x=:screwEx, screw_end_y=:screwEy, screw_end_z=:screwEz, center_x=:screwCx, "
    47. "center_y=:screwCy, center_z=:screwCz, screws_idscrews=:screw_type_id, "
    48. "screwPolyTransform=:screwPolyTransformStream, isEditedByDentist=:is_edited_by_dentist "
    49. "WHERE idteeth=:tooth_uid_db AND patients_idpatient=:id_patient");
    50.  
    51. //bind values which are exclusive to the UPDATE query
    52. query.bindValue(":tooth_uid_db",current_tooth->getTeethID());
    53. }
    54.  
    55. //bind values which are shared between the INSERT and UPDATE query
    56. query.bindValue(":screwSx",(float)current_tooth->getScrewStart_x_mm());
    57. query.bindValue(":screwSy",(float)current_tooth->getScrewStart_y_mm());
    58. query.bindValue(":screwSz",(float)current_tooth->getScrewStart_z_mm());
    59. query.bindValue(":screwEx",(float)current_tooth->getScrewEnd_x_mm());
    60. query.bindValue(":screwEy",(float)current_tooth->getScrewEnd_y_mm());
    61. query.bindValue(":screwEz",(float)current_tooth->getScrewEnd_z_mm());
    62. query.bindValue(":screwCx",(float)current_tooth->getScrewCenter_x_mm());
    63. query.bindValue(":screwCy",(float)current_tooth->getScrewCenter_y_mm());
    64. query.bindValue(":screwCz",(float)current_tooth->getScrewCenter_z_mm());
    65. query.bindValue(":screw_type_id",(int)current_tooth->getScrewTypeID()>0? current_tooth->getScrewTypeID():0);
    66. query.bindValue(":is_edited_by_dentist",(int)current_tooth->isScrewTypeSet());
    67. query.bindValue(":is_custom",(int)current_tooth->getIsCustomImplant());
    68. query.bindValue(":id_patient",(int)currentPatientRecord->getPatientsID());
    69. query.bindValue(":screwPolyTransformStream",qmatrixBA); //qmatrixBA is a QByteArray
    70.  
    71. if(!query.exec())
    72. {
    73. //query unsuccessful
    74. isQuerySuccess = false;
    75. error_message = "Database Text: " + db.lastError().databaseText()
    76. + ",Driver Text: " + db.lastError().driverText();
    77.  
    78. emit error(error_message);
    79. emit finished(isQuerySuccess);
    80. }
    81.  
    82. //----------------------------------------------------------------------------//
    83. //The following code prints the executed query with the variables replaced by actual values
    84. QString str = query.lastQuery();
    85. QMapIterator<QString, QVariant> it(query.boundValues());
    86. while (it.hasNext())
    87. {
    88. it.next();
    89. str.replace(it.key(), it.value().toString());
    90. }
    91. qDebug()<<str;
    92. //----------------------------------------------------------------------------//
    93. }
    94.  
    95. i++;
    96. }
    97.  
    98. //if we reached this point then all the queries have been executed without error
    99. emit finished(isQuerySuccess);
    100.  
    101. db.close();
    102. }
    103. else
    104. {
    105. //db failed to open
    106. isQuerySuccess = false;
    107. error_message = "Database Text: " + db.lastError().databaseText()
    108. + "Driver Text: " + db.lastError().driverText();
    109.  
    110. emit error(error_message);
    111. emit finished(isQuerySuccess);
    112. }
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  2. #2
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    Default Re: MySQL INSERT query fails in Qt

    Take a look into the server log.

  3. #3
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    Default Re: MySQL INSERT query fails in Qt

    Hello. I have extracted a section of SQL's log file showing the statements being executed. You can see 3 UPDATE queries successfully executed and 1 INSERT query failing. Note that I have split the statements in multiple lines for readability and replaced the contents of the blob with 'myBlob data'.

    Qt Code:
    1. 36 Connect myUsername@myDomainName.com on myDatabase
    2. 36 Init DB myDatabase
    3. 36 Query SET NAMES utf8
    4.  
    5. 36 Prepare UPDATE teeth SET screw_start_x=?, screw_start_y=?,
    6. screw_start_z=?, screw_end_x=?, screw_end_y=?, screw_end_z=?,
    7. center_x=?, center_y=?, center_z=?, screws_idscrews=?,
    8. screwPolyTransform=?, isEditedByDentist=?
    9. WHERE idteeth=? AND patients_idpatient=?
    10. 36 Reset stmt
    11. 36 Execute UPDATE teeth SET screw_start_x='94.4849',
    12. screw_start_y='63.4829', screw_start_z='27.4593',
    13. screw_end_x='94.4849', screw_end_y='63.4829', screw_end_z='17.4593',
    14. center_x='94.4849', center_y='63.4829', center_z='22.4593',
    15. screws_idscrews=13, screwPolyTransform='myBlob data', isEditedByDentist=1
    16. WHERE idteeth=136 AND patients_idpatient=30
    17. 36 Close stmt
    18.  
    19. 36 Prepare UPDATE teeth SET screw_start_x=?, screw_start_y=?,
    20. screw_start_z=?, screw_end_x=?, screw_end_y=?, screw_end_z=?,
    21. center_x=?, center_y=?, center_z=?, screws_idscrews=?,
    22. screwPolyTransform=?, isEditedByDentist=?
    23. WHERE idteeth=? AND patients_idpatient=?
    24. 36 Reset stmt
    25. 36 Execute UPDATE teeth SET screw_start_x='96.5366',
    26. screw_start_y='69.6727', screw_start_z='26.6544',
    27. screw_end_x='96.5366', screw_end_y='69.6727', screw_end_z='15.6544',
    28. center_x='96.5366', center_y='69.6727', center_z='21.1544',
    29. screws_idscrews=20, screwPolyTransform='myBlob data', isEditedByDentist=1
    30. WHERE idteeth=137 AND patients_idpatient=30
    31. 36 Close stmt
    32.  
    33. 36 Prepare UPDATE teeth SET screw_start_x=?, screw_start_y=?,
    34. screw_start_z=?, screw_end_x=?, screw_end_y=?, screw_end_z=?,
    35. center_x=?, center_y=?, center_z=?, screws_idscrews=?,
    36. screwPolyTransform=?, isEditedByDentist=?
    37. WHERE idteeth=? AND patients_idpatient=?
    38. 36 Reset stmt
    39. 36 Execute UPDATE teeth SET screw_start_x='99.6178',
    40. screw_start_y='74.014', screw_start_z='22.1863',
    41. screw_end_x='100.883', screw_end_y='77.8087', screw_end_z='15.2581',
    42. center_x='100.25', center_y='75.9113', center_z='18.7222',
    43. screws_idscrews=7, screwPolyTransform='myBlob data', isEditedByDentist=1
    44. WHERE idteeth=138 AND patients_idpatient=30
    45. 36 Close stmt
    46.  
    47. 36 Prepare INSERT INTO teeth (patients_idpatient, location, screw_start_x,
    48. screw_start_y, screw_start_z, screw_end_x, screw_end_y, screw_end_z,
    49. center_x, center_y, center_z, screws_idscrews, screwPolyTransform,
    50. isEditedByDentist, isCustomImplant)
    51. VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
    52. 36 Reset stmt
    53.  
    54. 36 Quit
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  4. #4
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    Default Re: MySQL INSERT query fails in Qt

    Hi, QSqlQuery:repare, and QSqlQuery::exec return boolean results indicating success or failure. I see that you are only checking the result of the query.exec() call. Try examining the result of the prepare methods to ensure they are all successful.

    Good luck.

    Jeff

  5. #5
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    Default Re: MySQL INSERT query fails in Qt

    Quote Originally Posted by jthomps View Post
    Hi, QSqlQuery:repare, and QSqlQuery::exec return boolean results indicating success or failure. I see that you are only checking the result of the query.exec() call. Try examining the result of the prepare methods to ensure they are all successful.

    Good luck.

    Jeff
    Hello. I have checked the return values of the QSqlQuery:repare as you recommended. The query is prepared successfully i.e. query.prepare() returns true.

  6. #6
    Join Date
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    Default Re: MySQL INSERT query fails in Qt

    After days of struggling I ve managed to solve the issue. It was a stupid mistake I had done in the code shown above and unfortunately quite difficult to detect since I was not getting any kind of error message, except from the INSERT query failing. I am posting the solution below:

    The problem was caused by line 65 of the code:
    Qt Code:
    1. query.bindValue(":screw_type_id",(int)current_tooth->getScrewTypeID()>0? current_tooth->getScrewTypeID():0);
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    and it is related to the column
    Qt Code:
    1. [int(11)]screws_idscrews,
    To copy to clipboard, switch view to plain text mode 
    of the SQL table. This column is a foreign key to another table. Therefore, it is automatically constraint not to take any values that will point to non-existent entries in the other table. As a result, the conditional statement above failed when it returned 0, since the foreign key cannot take the value 0 as it was setup. The correct value that the statement should return is NULL. To do this, line 65 was changed to this:
    Qt Code:
    1. query.bindValue(":screw_type_id",current_tooth->getScrewTypeID()>0? current_tooth->getScrewTypeID():QVariant(QVariant::Int));
    To copy to clipboard, switch view to plain text mode 
    This solved the problem.

    Simply using NULL as the 2nd argument to QSqlQuery::bindValue() does not work. According to the documentation of QSqlQuery::bindValue()
    To bind a NULL value, use a null QVariant
    .
    Here, the column screws_idscrews is of type INT so the following must be used to get a NULL INT:
    Qt Code:
    To copy to clipboard, switch view to plain text mode 

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