96 lines
4.8 KiB
C++
96 lines
4.8 KiB
C++
#pragma once
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#include "ILog.h"
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// this is pure virtual interface base class between sqlite3, which speaks only C and utf8 char[]
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// and wxWidgets which speaks only C++ and unicode strings.
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// Usage: Call the factory function std::shared_ptr<ISqlite3> sqlite3_open(const char *) to get a shared
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// pointer to the // Sqlite3 database object. Then call the factory function
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// sqlite3_prepare(std::shared_ptr<ISqlite3>, const char *) to get a unique pointer to
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// a compiled SQL statement
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// Its primary purpose is to avoid code that needs both the wxWidgets header files,
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// and the sqlite3.h header file.
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//
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// It speaks only utf8 char[], and needs to be called in wxWidgets code using
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// wxString.utf8_str() and its return values need to be interpreted in wxWidgets code
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// using wxString::FromUTF8().
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//
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// This header file can be included in code that has the sqlite3.h header file
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// and in code that has the wxWidgets header file, for it has no dependencies on either one
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//
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// In code that has wxWidgets headers, we call members of this interface class,
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// rather than directly calling sqlite3 functions.
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//
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// I originally implemented the pimpl idiom, but it turns out that pimpl has become
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// substantially more difficult in C++14, because one is effectively rolling one's own
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// unique pointer.
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//
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// It is therefore easier to implement a pure virtual base class with a virtual destructor and
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// factory function that returns a smart pointer to a member of the derived implementation
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//
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/* This code is at a low level abstraction, because it provides low level C++ interface to inherently low level C
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It is intended to be wrapped in higher level code that does not know about the nuts and bolts of sqlite3, but which supports throwing, templated functions, and all that.*/
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//
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//___________________________________
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// This class wraps a compiled sql statement.
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class Icompiled_sql
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{
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protected:
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Icompiled_sql() = default; // needed for derived constructor
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public:
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virtual ~Icompiled_sql() = default; // needed for derived destructor
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// Bind is used when writing stuff into the database. These objects should continue to exist until the write is finalized or reset.
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virtual void Isqlite3_bind( int, const std::span<const uint8_t>) = 0; // https://sqlite.org/c3ref/bind.html
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virtual void Isqlite3_bind(int, int) = 0;
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virtual void Isqlite3_bind(int, int64_t) = 0;
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virtual void Isqlite3_bind(int) = 0;
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virtual void Isqlite3_bind(int, const char*) = 0;
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enum sql_result { DONE, ROW, BUSY, SQL_ERROR, MISUSE };
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virtual sql_result Isqlite3_step() = 0;
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// when reading, you don't use bind. Sqlite creates a temporary in the memory that it manages. If you want the object to live beyond the next step operation, need to make a copy
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// When writing objects, we reinterpret a pointer to a typed object as a blob pointer, when reading them, we need a typed copy, otherwise calling the destructor could be bad.
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// We don't want Sqlite3 calling destructors on our objects, hence write them as static, and create them from raw bytes on reading.
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virtual std::span<const uint8_t> Isqlite3_column_blob (int) const = 0; // returns the null pointer and zero length if null.
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virtual int Isqlite3_column_int (int) const = 0;
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virtual int64_t Isqlite3_column_int64 (int) const = 0;
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virtual char* Isqlite3_column_text (int) const = 0; // returns pointer to zero length
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// string if null. If we need to distinguish betweem zero length strings and nulls, need the
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// type function.
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// We can store any type in any column, and read any type from any column, but if something
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// unexpected is in a column, it gets coerced to the expected type on being read back.
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// Thus something stored as a number and read back as blob will come back as the decimal character string.
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// It is very rarely valid to store different types in the same column, except that
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// null is permissible. The difference between null and zero matters, but the case of
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// null is usually dealt with by sql code, not C code.
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virtual void Isqlite3_reset() = 0; // https://sqlite.org/c3ref/reset.html
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};
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//___________________________________
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// This class wraps a database. Its derived implementation will hold an old type C pointer
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// to an opened database object, which is destroyed when the class object is destroyed
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class ISqlite3
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{
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protected:
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ISqlite3() = default; // needed for derived constructor
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public:
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virtual ~ISqlite3() = default; // needed for derived destructor
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virtual void exec(const char*) = 0;
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};
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// Factory method to open a database and produce a shared object wrapping the database
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ISqlite3* Sqlite3_open(const char*);
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// Factory method to create a database and produce a shared object wrapping the database
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ISqlite3* Sqlite3_create(const char*);
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// Factory method to prepare a compiled sql statement
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Icompiled_sql* sqlite3_prepare(ISqlite3*, const char *);
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void sqlite3_init();
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extern "C" {
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int sqlite3_shutdown(void);
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}
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