sqlite嵌入式数据库C语言基本操作(2)

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事实上对于操作sqlite的其他语言，写一个统一的数据库操作模型是非常容易的，比如java，c#，这些语言支持垃圾回收，支持异常捕获，支持泛型，写起来就很容易。但是对于C语言，就得另当别论了，就拿查询操作来说，c语言没有泛型，不能返回统一的泛型列表，只能返回数据模型的链表结构。

但是得益于前面讲过的通用链表)结构,我们可以尽可能的像其他语言一样封装一个通用的数据库操作模型。

回顾前面讲到的sqlite操作基本流程，查询流程是
1.打开数据库
2.准备好SQL语句。
3.绑定SQL语句参数
4.执行SQL语句
5.返回结果集，执行串链操作。
6.释放资源
7.关闭数据库句柄.
整体的流程不变，把不一样的部分抽象出来 —— 绑定参数，执行串链的过程抽象出来。

绑定参数，如

int bind_userinfo_t(sqlite3_stmt * stmt,int index, void * arg )

执行查询建链过程，如

int create_userinfo_T(sqlite3_stmt,void * arg)

然后在通用的数据库操作函数中传入函数指针，尽量的精简代码。
下面是的dbhelper.h 和 dbhelper.c 抽象的一般数据库操作函数。

#ifndef _DBHELPER_H_
#define _DBHELPER_H_
#include <sqlite3.h> 

#define DB_SQL_MAX_LEN 1024
//执行没有返回的SQL语句
int db_nonquery_operator(const char *sqlstr,int (*bind)(sqlite3_stmt *,int index,void * arg),void *param);
//执行没有返回的SQL语句的多值传参
int db_nonquery_by_varpara(const char *sql,const char *fmt,...);
//执行没有返回的SQL语句
int db_nonquery_transaction(int (*exec_sqls)(sqlite3 *db,void * arg),void *arg);
//执行多值传参的查询语句
int db_query_by_varpara(const char *sql,int (*create)(sqlite3_stmt *stmt,void *arg),void *arg,const char *fmt,...);
//执行查询并返回查询结果集的条数
int db_query_count_result(const char *sql);
//对sqlite3_column_blob的二次封装
int db_stmt_get_blob(sqlite3_stmt *stmt,int index,unsigned char *out);
//对sqlite3_column_text的二次封装
int db_stmt_get_text(sqlite3_stmt *stmt,int index,char *out);
//对sqlite3_column_int的二次封装
int db_stmt_get_int(sqlite3_stmt *stmt,int index);
//对sqlite3_column_double的二次封装
double db_stmt_get_double(sqlite3_stmt *stmt,int index);

#endif

dbhelper.c:

#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include "na_queue.h"
#include "dbhelper.h"

#define DB_NAME "test.db"

static pthread_mutex_t db_mutex_lock = PTHREAD_MUTEX_INITIALIZER;

static int db_bind_by_var(sqlite3_stmt *stmt,const char *fmt,va_list args)
{
    int len,npara=1;
    int ret = SQLITE_OK;
    if(fmt == NULL){
        return ret;
    }

       for(;*fmt;++fmt){
        if(*fmt != '%')
            continue;
        ++fmt;
        //get length
        len = 0;
        while(isdigit(*fmt)){
            len = len * 10 + (*fmt - '0');
            ++fmt;
        }
        switch(*fmt){
        case 'd':
            ret = sqlite3_bind_int(stmt,npara,va_arg(args,int));
            break;
        case 's':
            {
            char *str = va_arg(args,char *);
            ret = sqlite3_bind_text(stmt,npara,str,strlen(str),NULL);
            }
            break;
        case 'x':
            {
            unsigned char *pdata;
            pdata = va_arg(args,char *);
            ret = sqlite3_bind_blob(stmt,npara,pdata,len,NULL);
        //    printf_phex("blob",pdata,len);
            }
            break;
        default:
            ret = SQLITE_ERROR;
            break;
        }
        ++npara;
        if(ret)
            return ret;
    }
    return ret;
}

/*
 * ===  FUNCTION  ======================================================================
 *         Name:  db_query_by_varpara
 *  Description:  数据库查询操作，可以带变参绑定
 *  @sql       :  sql
 *  @create    :  取得数据并创建节点
 *  @arg       :  用户用于create的参数
 *  @fmt       :  格式字符串，%s string,%d int,%nx 长度为N的二进制串
 *  ...        :  变参
 *  Return     :  查询到数据的条数
 * =====================================================================================
 */
int db_query_by_varpara(const char *sql,int (*create)(sqlite3_stmt *stmt,void *arg),void *arg,const char *fmt,...)
{
    sqlite3 *db = NULL;
    sqlite3_stmt *stmt = NULL;
    if(sql == NULL){
//        return SQLITE_ERROR;
        return 0;
    }
    pthread_mutex_lock(&db_mutex_lock);
    int rc = sqlite3_open(DB_NAME,&db);
    if(rc != SQLITE_OK){
        printf("open database failed,rc=%d",rc);
        pthread_mutex_unlock(&db_mutex_lock);
        return 0;
    }

    rc = sqlite3_prepare(db,sql,-1,&stmt,NULL);
    if(rc != SQLITE_OK){
        printf("database prepare fail,rc=%d",rc);
        goto DB_EXEC_FAIL;
    }

    if(fmt){
        va_list args;
        va_start(args,fmt);
        rc = db_bind_by_var(stmt,fmt,args);
        va_end(args);
        if(rc){
            printf("database bind fail,rc=%d",rc);
            goto DB_EXEC_FAIL;
        }
    }

    if(create){
        rc = (*create)(stmt,arg);
    }else{
        rc = (sqlite3_step(stmt),0);
    }
    sqlite3_finalize(stmt);
    goto DB_EXEC_OK;
DB_EXEC_FAIL:
    printf("db operator failed,rc=%d",rc);
    rc = 0;
DB_EXEC_OK:
    sqlite3_close(db);
    pthread_mutex_unlock(&db_mutex_lock);
    return rc;
}

/*
 * ===  FUNCTION  ======================================================================
 *         Name:  db_exec_noquery
 *  Description:  执行非查询操作
 *  @sqlstr    :  sql,多条语句由';'分开
 *  @bind      :  绑定sql中的未知变量操作
 *  @param     :  绑定中的参数
 *  @bind.index:  sql语句序号
 *  Return     :  0 or error
 * =====================================================================================
 */
int db_nonquery_operator(const char *sqlstr,int (*bind)(sqlite3_stmt *,int index,void * arg),void *param)
{
    sqlite3 *db = NULL;
    sqlite3_stmt *stmt = NULL;
//    char *emsg = NULL;
    if(sqlstr == NULL){
        return SQLITE_ERROR;
    }
    pthread_mutex_lock(&db_mutex_lock);
    int rc = sqlite3_open(DB_NAME,&db);
    if(rc != SQLITE_OK){
        printf("open database failed,rc=%d",rc);
        pthread_mutex_unlock(&db_mutex_lock);
        return rc;
    }
    rc = sqlite3_exec(db,"begin transaction",0,0,NULL);
    if(rc != SQLITE_OK){
        printf("begin transaction:ret=%d",rc);
        goto DB_BEGIN_FAIL;
    }
    char sql[DB_SQL_MAX_LEN];
    int index = 0,offset=0,n=0;
    while(sqlstr[index] != 0){
        offset = 0;
        do{
            if(offset >= DB_SQL_MAX_LEN){
                printf("sql is too long,(%d)",offset);
                rc = SQLITE_ERROR;
                goto DB_EXEC_FAIL;
            }
            if((sqlstr[index] != ';') && (sqlstr[index] != 0)){
                sql[offset++] = sqlstr[index++];
            }else{
                sql[offset] = '\0';
                if(sqlstr[index] == ';') index++;
                n++;
                break;
            }
        }while(1);
        printf("sql:%s",sql);
        rc = sqlite3_prepare(db,sql,-1,&stmt,NULL);
        if(rc != SQLITE_OK){
            printf("prepare,error,%d",rc);
            goto DB_EXEC_FAIL;
        }
        if(bind){
            rc = (*bind)(stmt,n,param);
        }else{
            rc = sqlite3_step(stmt);
        }
        sqlite3_finalize(stmt);
        if((rc != SQLITE_OK) && (rc != SQLITE_DONE)){
            printf("bind");
            goto DB_EXEC_FAIL;
        }
    }
    rc = sqlite3_exec(db,"commit transaction",0,0,NULL);
    if(rc){
        printf("commit transaction:%d",rc);
        goto DB_EXEC_FAIL;
    }
    goto DB_EXEC_OK;
DB_EXEC_FAIL:
    if(sqlite3_exec(db,"rollback transaction",0,0,NULL)){
        printf("rollback transaction error");
    }
DB_BEGIN_FAIL:
//    sqlite3_free(emsg);
    printf("db operator failed,rc=%d",rc);
DB_EXEC_OK:
    sqlite3_close(db);
    pthread_mutex_unlock(&db_mutex_lock);
    return rc;
}

int db_nonquery_by_varpara(const char *sql,const char *fmt,...)
{
    sqlite3 *db = NULL;
    sqlite3_stmt *stmt = NULL;
    if(sql == NULL){
        return SQLITE_ERROR;
    }
    pthread_mutex_lock(&db_mutex_lock);
    int rc = sqlite3_open(DB_NAME,&db);
    if(rc != SQLITE_OK){
        printf("open database failed,rc=%d",rc);
        pthread_mutex_unlock(&db_mutex_lock);
        return rc;
    }
    printf("sql:%s",sql);
    rc = sqlite3_prepare(db,sql,-1,&stmt,NULL);
    if(rc != SQLITE_OK){
        printf("prepare,");
        goto DB_EXEC_FAIL;
    }
    if(fmt){
        va_list args;
        va_start(args,fmt);
        rc = db_bind_by_var(stmt,fmt,args);
        va_end(args);
        if(rc){
            goto DB_EXEC_FAIL;
        }
    }
    rc = sqlite3_step(stmt);
    sqlite3_finalize(stmt);
    if((rc != SQLITE_OK) && (rc != SQLITE_DONE)){
        printf("bind");
        goto DB_EXEC_FAIL;
    }
    rc = 0;
    goto DB_EXEC_OK;
DB_EXEC_FAIL:
DB_BEGIN_FAIL:
    printf("db operator failed,rc=%d",rc);
DB_EXEC_OK:
    sqlite3_close(db);
    pthread_mutex_unlock(&db_mutex_lock);
    return rc;
}

int db_nonquery_transaction(int (*exec_sqls)(sqlite3 *db,void * arg),void *arg)
{
    sqlite3 *db = NULL;
    sqlite3_stmt *stmt = NULL;
//    char *emsg = NULL;
    pthread_mutex_lock(&db_mutex_lock);
    int rc = sqlite3_open(DB_NAME,&db);
    if(rc != SQLITE_OK){
        printf("open database failed,rc=%d",rc);
        pthread_mutex_unlock(&db_mutex_lock);
        return rc;
    }
    rc = sqlite3_exec(db,"begin transaction",0,0,NULL);
    if(rc != SQLITE_OK){
        printf("begin transaction:%d",rc);
        goto DB_BEGIN_FAIL;
    }

    if(exec_sqls){
        rc = (*exec_sqls)(db,arg);
    }else{
        rc = SQLITE_ERROR;
    }
    if((rc != SQLITE_OK) && (rc != SQLITE_DONE)){
        printf("prepare,error,%d",rc);
        goto DB_EXEC_FAIL;
    }

    rc = sqlite3_exec(db,"commit transaction",0,0,NULL);
    if(rc){
        printf("commit transaction:%d",rc);
        goto DB_EXEC_FAIL;
    }
    goto DB_EXEC_OK;
DB_EXEC_FAIL:
    if(sqlite3_exec(db,"rollback transaction",0,0,NULL)){
        printf("rollback transaction:error");
    }
DB_BEGIN_FAIL:
//    sqlite3_free(emsg);
    printf("db operator failed,rc=%d",rc);
DB_EXEC_OK:
    sqlite3_close(db);
    pthread_mutex_unlock(&db_mutex_lock);
    return rc;
}

static int db_get_count(sqlite3_stmt *stmt,void *arg)
{
    int ret,*count=arg;
    ret = sqlite3_step(stmt);
    if(ret != SQLITE_ROW)
        return SQLITE_EMPTY;
    *count = db_stmt_get_int(stmt,0);
    return SQLITE_OK;
}

/*
 * ===  FUNCTION  ======================================================================
 *         Name:  db_query_count_result
 *  Description:  查询计数结果的第一列第一行，其它忽略
 *  @sql       :  查询计数的SQL语句
 *  Return     :  查询到计数返回计数，否则一律返回0
 * =====================================================================================
 */
int db_query_count_result(const char *sql)
{
    int ret,count=0;
    ret = db_query_by_varpara(sql,db_get_count,&count,NULL);
    if(ret == SQLITE_OK)
        return count;
    return 0;
}

int db_stmt_get_blob(sqlite3_stmt *stmt,int index,unsigned char *out)
{
    const char *pdata = sqlite3_column_blob(stmt,index);
    int len = sqlite3_column_bytes(stmt,index);
    if(pdata){
        memcpy(out,pdata,len);
        return len;
    }
    return 0;
}

int db_stmt_get_text(sqlite3_stmt *stmt,int index,char *out)
{
    const unsigned char *pdata = sqlite3_column_text(stmt,index);
    if(pdata){
        int len = strlen(pdata);
        strncpy(out,pdata,len);
        return len;
    }
    return 0;
}

int db_stmt_get_int(sqlite3_stmt *stmt,int index)
{
    return sqlite3_column_int(stmt,index);
}

double db_stmt_get_double(sqlite3_stmt *stmt,int index)
{
    return sqlite3_column_double(stmt,index);
}

对以上的代码做一下说明:
test.db为数据库文件

为了处理多线程，在对数据库进行操作的时候加了锁。

现在按照通用数据库操作方式重写上次的代码，查询和增加操作。

首先重写数据模型：

typedef struct userinfo_s{
    int userid;
    char username[32];
    na_queue_t queue;
}userinfo_t;

释放函数链表函数：

 void free_userinfo_t(na_queue_t *h){
    na_queue_t *head = h,*pos,*n;
    userinfo_t *p = NULL;
    na_queue_for_each_safe(pos,n,head){
        p = na_queue_data(pos,userinfo_t,queue);
        free(p);
    }
    na_queue_init(head);
 }

绑定函数，用于绑定insert的插入函数

int bind_userinfo_t(sqlite3_stmt * stmt,int index,void * arg){
        int rc;
        userinfo_t * param = arg;
        sqlite3_bind_int(stmt,1,param->userid);
        sqlite3_bind_text(stmt,2,param->username,strlen(param->username),NULL);
        rc = sqlite3_step(stmt);
        if (rc != SQLITE_DONE)
                return rc;
        return SQLITE_OK;
}

查询操作需要的串链函数：

int create_userinfo_t(sqlite3_stmt * stmt,void * arg){
        na_queue_t * h = arg;
        na_queue_init(h);
        userinfo_t * u;
        int ret,count = 0;
        ret = sqlite3_step(stmt);
        if(ret != SQLITE_ROW){
                return 0;
        }
        do
        {
                u = calloc(sizeof(userinfo_t),1);
                if(!u){
                        goto CREATE_USERINFO_FAIL;
                }
                u->userid = db_stmt_get_int(stmt,0);
                db_stmt_get_text(stmt,1,u->username);
                na_queue_insert_tail(h,&(u->queue));
                count ++;
        } while ((ret = sqlite3_step(stmt)) == SQLITE_ROW);
        return count;
CREATE_USERINFO_FAIL:
        free_userinfo_t(h);
        return 0;
}

基本的对数据表的操作就是按照这种方式来抽象代码,现在我们来按照这种方式来写一段测试代码:

//打印用户信息
void printusers(na_queue_t *h){
        userinfo_t * q=NULL;
        na_queue_foreach(q,h,userinfo_t,queue){
                printf("userid:%d username:%s\n",q->userid,q->username);
        }
}

//得到所以用户信息
int get_all_userinfo(na_queue_t * h){
        return db_query_by_varpara("select * from userinfo;",create_userinfo_t,h,NULL);
}

//添加一个用户信息
int add_a_userinfo(userinfo_t * u){
        return db_nonquery_operator("insert into userinfo(userid,username) values (?,?)",bind_userinfo_t,u);
}

int main(int argc, char *argv[])
{
        printf("test get all userinfo\n");
        na_queue_t h;
        int ret = get_all_userinfo(&h);
        printusers(&h);
        free_userinfo_t(&h);
        printf("test add userinfo");
        userinfo_t newuser;
        newuser.userid = 7;
        strncpy(newuser.username,"White",10);
        add_a_userinfo(&newuser);
        get_all_userinfo(&h);
        printusers(&h);
        free_userinfo_t(&h);
        return 0;
}

我们还是上一次的数据库来接着运行，输出：

test get all userinfo
userid:1 username:Alex

userid:2 username:Neo

userid:3 username:Allan

userid:4 username:coby

userid:5 username:micheal

test add userinfo

userid:1 username:Alex

userid:2 username:Neo

userid:3 username:Allan

userid:4 username:coby

userid:5 username:micheal

userid:7 username:White

以上就是一个简单的C语言对SQLITE数据库操作的封装，事实上我们已经把它用在了我们的生产环境，不过生产环境版本相对于这个版本要复杂一点，加入的日志模块，线程模块，而且现在还在继续进化中，但是原理就是这样了，实现上大同小异而已。实例也同样只是写了查询和插入，至于其他操作就有读者自己在这个实例上去添加了。SQLITE小型数据库相对与其他Oracle等其他大型数据库而言，他对SQL的支持没有他们强大，但是对于小型嵌入式系统已经足够了，他们之间的差异只有改天再补充了。今天就到这了。

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