libzdb c语言的数据库连接池支持库 源码分析

libzdb c语言的数据库连接池支持库 源码分析

Standard

整个程序可以支持各种数据库，是通过“接口实现的”。

而C语言并没有接口的概念，它是如何实现的呢？

在ConnectionDelegate.h文件里定义了一个结构体，这个结构体是保存一个数据库连接的所有信息和操作方法，这里的方法都是使用函数指针来定义的。

typedef struct Cop_T { const char *name; // Event handler class methods void (*onstop)(void); // Methods T (*new)(URL_T url, char **error); void (*free)(T *C); void (*setQueryTimeout)(T C, int ms); void (*setMaxRows)(T C, int max); int (*ping)(T C); int (*beginTransaction)(T C); int (*commit)(T C); int (*rollback)(T C); long long int (*lastRowId)(T C); long long int (*rowsChanged)(T C); int (*execute)(T C, const char *sql, va_list ap); ResultSet_T (*executeQuery)(T C, const char *sql, va_list ap); PreparedStatement_T (*prepareStatement)(T C, const char *sql, va_list ap); const char *(*getLastError)(T C); } *Cop_T;

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typedef struct Cop_T {                                                                   const char *name;                                                                 // Event handler class methods                                                   void (*onstop)(void);                                                             // Methods                                                                   T (*new)(URL_T url, char **error);                                               void (*free)(T *C);                                                               void (*setQueryTimeout)(T C, int ms);                                                 void (*setMaxRows)(T C, int max);                                                 int (*ping)(T C);                                                                 int (*beginTransaction)(T C);                                                     int (*commit)(T C);                                                           int (*rollback)(T C);                                                             long long int (*lastRowId)(T C);                                                 long long int (*rowsChanged)(T C);                                               int (*execute)(T C, const char *sql, va_list ap);                                 ResultSet_T (*executeQuery)(T C, const char *sql, va_list ap);                       PreparedStatement_T (*prepareStatement)(T C, const char *sql, va_list ap);         const char *(*getLastError)(T C);                                         } *Cop_T;

而在每种数据库实现时，使用这种结构体定义时，分别赋予了每种数据库对应的函数操作方法，这样就实现了接口的定义。

const struct Cop_T mysqlcops = { "mysql", onstop, MysqlConnection_new, MysqlConnection_free, MysqlConnection_setQueryTimeout, MysqlConnection_setMaxRows, MysqlConnection_ping, MysqlConnection_beginTransaction, MysqlConnection_commit, MysqlConnection_rollback, MysqlConnection_lastRowId, MysqlConnection_rowsChanged, MysqlConnection_execute, MysqlConnection_executeQuery, MysqlConnection_prepareStatement, MysqlConnection_getLastError };

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const struct Cop_T mysqlcops = {                 "mysql",                                 onstop,                                 MysqlConnection_new,                     MysqlConnection_free,                   MysqlConnection_setQueryTimeout,         MysqlConnection_setMaxRows,             MysqlConnection_ping,                   MysqlConnection_beginTransaction,         MysqlConnection_commit,                 MysqlConnection_rollback,               MysqlConnection_lastRowId,               MysqlConnection_rowsChanged,             MysqlConnection_execute,                 MysqlConnection_executeQuery,           MysqlConnection_prepareStatement,         MysqlConnection_getLastError     };

结构体中虽然存储的是数据，但是这个数据如果是指针类型，那么他的作用就不仅仅能够赋值了。这里的“接口”，实质就是对函数指针的灵活运用。

使用方法

// 首先初始化数据库连接池 URL_T url = URL_new("mysql://localhost/test?user=root&password=swordfish"); //设置连接url ConnectionPool_T pool = ConnectionPool_new(url); //新建一个连接池结构体，并分配内存 ConnectionPool_start(pool); //初始化连接池（建立连接），调用fillpool //... Connection_T con = ConnectionPool_getConnection(pool); //从连接池获取一个连接 ResultSet_T result = Connection_executeQuery(con, "select id, name, image from employee where salary>%d", anumber); //使用此连接执行查询数据操作 while (ResultSet_next(result)) { int id = ResultSet_getInt(result, 1); const char *name = ResultSet_getString(result, 2); int blobSize; const void *image = ResultSet_getBlob(result, 3, &blobSize); //... } Connection_close(con); //连接使用完关闭连接 //... ConnectionPool_free(&pool); //关闭连接池 URL_free(&url);

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//首先初始化数据库连接池 URL_T url = URL_new("mysql://localhost/test?user=root&password=swordfish");   //设置连接url ConnectionPool_T pool = ConnectionPool_new(url);   //新建一个连接池结构体，并分配内存 ConnectionPool_start(pool);   //初始化连接池（建立连接），调用fillpool //... Connection_T con = ConnectionPool_getConnection(pool);   //从连接池获取一个连接 ResultSet_T result = Connection_executeQuery(con, "select id, name, image from employee where salary>%d", anumber);   //使用此连接执行查询数据操作 while (ResultSet_next(result)) {       int id = ResultSet_getInt(result, 1);       const char *name = ResultSet_getString(result, 2);       int blobSize;       const void *image = ResultSet_getBlob(result, 3, &blobSize);       //... } Connection_close(con);   //连接使用完关闭连接 //... ConnectionPool_free(&pool);   //关闭连接池 URL_free(&url);