nim-qt5_qtsql

Nim binding for Qt 5's Qt SQL library that integrates with the features of the Nim language.

Features

• Production-ready
• All of the features that you would expect from Qt SQL
  • Such as a single API for multiple database engines
  • And support for prepared statements
• Utilizes features of the Nim language for easier usage
• Avoids complexity by utilizing C++'s type system
  • For instance, instead of providing full bindings for QVariant, this provides a minimal binding and lets C++'s type system take care of converting to and from QVariant objects automatically.
• Abstracts certain Qt behaviors that are not Nim-like, and presents a Nim-like API.

Qt Type Conversions

Qt uses a system of default values, null properties, and invalid properties to indicate the failure of a type conversion. The objects and values produced by failed conversions often function like regular objects and values, but produce unexpected results when used. This behavior leads to a silent failure situation if the result of a Qt type conversion is not checked properly by the program.

In Nim, most type conversion errors are not possible due to the type system and compiler checks. When it is impossible for a type conversion error to be checked at runtime, the Nim runtime and most Nim procedures will raise exceptions, which prevents silent failure situations.

nim-qt5_qtsql abstracts the Qt behavior and changes it to the Nim behavior. When possible, the binding checks for default values, null properties, and invalid properties after Qt type conversions. If these are present, the binding will throw a QObjectConversionError, which inherits from Nim's ObjectConversionError. Default values, null properties, and invalid properties are only checked for type conversions. Programs can still purposefully create Qt objects with default values, null properties, and invalid properties.

Known Limitations

• Qt SQL does not deep copy QSqlQuery objects, so they must be kept in scope on the stack during usage.
• Automatic conversions from Qt types to Nim types are temporarily disabled in version 1.1.x of the binding.
  • The Nim 0.17.0 compiler produces buggy code for procedures that return C++ objects. This has been worked around, but the work around requires changing converters to procs, which disables automatic conversion. Manual conversion is still possible by calling the conversion procedures in the binding.
    • See nim-lang/Nim#5140 for more details.

Usage

See qt5_qtsql/tests/sqlcat.nim for an example program that reads and writes a SQLite database.

License

This project is licensed under the MIT License. For full license text, see LICENSE.