Sql session qt cs
- 1. April 20, 2011Qt SQL moduleSAINT adaptations & workaroundsAndré Somers | 1
- 2. André Somers | 2 | SAINT database layer : Design and RationaleDatabase use caseSituation:All data stored in Relational Database, one database foreachstudyOriginallyusingMS AccessMaking database independent; first target MySqlProblem: SQL dialectsDifferent names and limitationsfor data typesSolution: No actual SQL code in codeQuery textsgeneratedby (extended) SQL driverforQt
- 3. André Somers | 3 | SAINT database layer : Design and RationaleQt & DatabasesQt drivers do not support DDL by defaultNo way to generate SQL to manipulate data structuresSolution: custom extension to Qt SQL driver modelQt SQL drivers are pluginsNew drivers subclassed from standard driver (so they can still be used where you’d otherwise use other drivers), but have an extended base to allow for more functionality.
- 4. André Somers | 4 | SAINT database layer : Design and RationaleSAINT extended Qt DB driversStandard QtSAINT extended driversQSqlDriverSqlDriverExtQODBCDriverAccessDriverQMySqlDriverMySqlDriverOther driverFuture other drivers
- 5. André Somers | 5 | SAINT database layer : Design and RationaleSAINT extended Qt DB drivers 2//createtable (simplified)QSqlRecordrecord;foreach (QSqlField field, table->fieldList) {record.append(field);}foreach(QStringrelationName, table->fkRelations) {Relation* rel = m_relations.value(relationName);QSqlFieldfkField(QString("%1_%2") .arg(tableName(rel->tableOne)) .arg(rel->fieldOne), QVariant::UInt);fkField.setLength(30);record.append(fkField);}sql= m_sqlDriver->sqlStatement(SqlDriverExt::CreateTableStatement, table->name, record);QSqlQueryquery(sql, m_db);Construct object-based representation of the desired table structureSqlDriverExt instanceOne of the new sqlStatement typesUse representation to create SQL
- 6. New DDL statement typesCreateTableStatementAlterTableAddFieldStatementAlterTableDropFieldStatementAlterTableModifyFieldStatementDropTableStatementCreateViewStatementDropViewStatementCreateIndexStatementDropDatabaseStatement
- 7. Other added featuresCreate-if-not-existsUse database templatesList databases on a serverRAII class for transactionsReturn information on installed drivers:Human readable nameIconServer or file basedDefault settings for UI (like standard port number)Workarounds for some smaller Qt SQL issues
- 8. Unifying the UIGoals:Unified way to select a database independent of the typeKeep history of recently used databases for easy re-selectingRe-usable components for selection for integration in all toolsTreat all the information on a database as a single unit of informationAvoid special-casing for different types of databases
- 9. Resulting UIAndré Somers | 9 | SAINT database layer: design and rationaleDrop-down box for easy re-selecting recently used databasesAccess to more databasesList is provided by proxy on custom modelIcons representing database typeUnique alias for each used database
- 10. Resulting UI (cont)André Somers | 10 | SAINT database layer: design and rationaleTabs to switch between already used databases and other databasesSortableFilter on alias Human-readable dates and times of last use
- 11. Resulting UI (cont)André Somers | 11 | SAINT database layer: design and rationaleDrop down with discovered database driversFile selector dialogRecently used filesDatabase alias (auto suggested)
- 12. Resulting UI (cont)André Somers | 12 | SAINT database layer: design and rationaleExisting databases on selected server
- 13. DatabaseDescription classPropertiesQString driverNameQString fileNameQString hostQString hostAliasint port QString userQString passwordQString databaseNameQString aliasQDateTime lastAccessMethodsbool exists()bool isValid()State state()QSqlDatabase sqlDatabase(const Qstring&)SqlDriverExt::DriverInfo driverInfo()bool dropDatabase()OperatorsQDataStream& operator<<(QDataStream&, const DatabaseDescription&)QDataStream& operator>>(QDataStream&, DatabaseDescription&)
- 14. TransactionsPerfect candidate for RAIICreating an instance on a QSqlDatabase begins a transactionExplicitly call commit() method to mark successful end of transactionIf goes out of scope before commit is called, it tries a roll-back.André Somers | 14 | SAINT database layer: design and rationale
- 15. Transaction RAII classclassSqltransaction {public:explicitSqlTransaction(QSqlDriver* driver); ~SqlTransaction();QSqlDriver* driver() {return m_driver;}inlineboolinTransaction() {return m_inTransaction;}inlineboolactive() {return m_inTransaction;}boolrollBack();boolcommit();boolcommitOrRollBack();boolsupported();private: //...};André Somers | 15 | SAINT database layer: design and rationale
- 16. Succes?Almost all database-dependent code has been removed from the code that is not part of the database layer presented.Still some pieces of code like this:Separate database template files are still neededAll in all: pretty good, and certainly workableAndré Somers | 16 | SAINT database layer: design and rationale
- 17. Remaining problemsDocumentation in Qt is lacking on thisApproach is quite low-level. Higher level would be niceQuery construction primitives are very basic:No sortingOnly = operator in WHERE statementsNo limitingNot asyncAndré Somers | 17 | SAINT database layer: design and rationale
- 18. ThanksThank you for your attention.Questions & Discussion:What issues remain for you?André Somers | 18 | SAINT database layer: design and rationale
- 19. André Somers | 19 | SAINT database layer: design and rationale
- 20. André Somers | 20 | SAINT database layer: design and rationale
- 21. Bio-energy, 2008-2009, 8414 publications, approx. 187400 links, in Gephi using Force Atlas. Image: E. Horlings.