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View Model

Creating a ViewModel

Let's look at how to create a ViewModel. The code is as follows:

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// PersonModel.h
#pragma once

#include "rdb/model/IRdbViewModelInterface.h"
#include "PersonView.h"
#include "SqliteDb.h"

class PersonModel : public IRdbViewModelInterface<PersonModel, PersonView, SqliteDb>
{
public:
    StudentModel() = default;
};
// PersonModel.cpp
#include "PersonModel.h"

The code is as concise and clear as ever. In the .h file, inherit from IRdbViewModelInterface to create an object, and include the header file in the .cpp file to ensure the object is recognized and compiled by the compiler.

IRdbViewModelInterface

Its implementation is as follows:

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template<typename T, typename View, typename Db, bool enabled = true>
class IRdbViewModelInterface
    : public IRdbEntityModelWare<View, Db>, public ITaskWareUnit<T, IRdbCatagory, enabled>
{
public:
    IRdbViewModelInterface();

public:
    virtual QString createViewSql() const;

protected:
    virtual double $order() const override;
    virtual void $task() final;

protected:
    const IRdbViewInfo& m_viewInfo;
};

This base class is a CRTP base class. The first parameter is the name of the Model subclass, the second parameter is the type of the corresponding View, the third parameter is the Database type, and the fourth parameter indicates whether to initialize and use the $task functionality.

Its inheritance classes are the following two: IRdbEntityModelWare and ITaskWareUnit.

IRdbEntityModelWare

This class was also used in the TableModel. It provides some basic query functions. Its content is as follows:

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template<typename Entity, typename Db>
class IRdbEntityModelWare
{
public:
    IRdbEntityModelWare();

public:
    std::size_t count();
    std::size_t count(const IRdbCondition&);

public:
    IResult<Entity> findOne(const IRdbCondition&);
    QList<Entity> findAll();
    QList<Entity> findAll(const IRdbCondition&);
    QVariantList findColumn(const QString& column);
    QVariantList findColumn(const QString& column, const IRdbCondition& condition);
    QList<QVariantMap> findColumns(const QStringList& columns);
    QList<QVariantMap> findColumns(const QStringList& columns, const IRdbCondition& condition);

public:
    bool exist(const IRdbCondition& condition);

public:
    ISqlQuery createQuery();
    ISqlQuery createQuery(const QString& sql);
    ISqlQuery createQuery(const QString& sql, const QVariantMap& values);

protected:
    IRdbDatabaseWare& m_database;
    const IRdbEntityInfo& m_entityInfo;
    const IRdbDialectWare& m_dialect;
};

As can be seen, it implements the count() for statistics, various find query functions, and the exist() function for checking existence. Specific functional details are not elaborated upon here.

Task

In addition to query functionality, the most important feature of IRdbViewModelInterface is the View table creation functionality, which is implemented in the Task. ITaskWareUnit registers the $task() implemented by the current class to ITaskManage, and ITaskManage executes these $task()s according to certain rules. In our overridden $task(), the following operations are performed:

  • Check if the view exists; if not, attempt to create the View.
  • It first calls the IRdbViewModelInterface::createViewSql() method to return a statement; if the statement is not empty, it executes it.
  • If the above statement is empty, it tries to check if the View provides SQL. The View provides SQL through the $CreateViewSql macro annotation. If the SQL exists, it executes it to create the View.
  • If the View still does not exist, it reports an error, prompting the user to provide a statement or manually create the View in the database.

Example

Here is an example illustrating its specific usage.

```cpp //TODO: