checkpoint

此函数通过创建索引节点和/或其他必要任务来完成一个或多个 put 操作，从而将对象的新值或更新后的值整合到数据库中。

    MCO_RET	classname_checkpoint(	
    	/*IN*/ classname * handle  
    );

参数

handle

classname *

类句柄类型变量的地址。

返回

MCO_S_OK

日志含义对象更新成功。

MCO_E_ACCESS

事务句柄为MCO_READ_ONLY。

MCO_E_TRANSACT

发生事务错误。

MCO_E_DELETED

该对象已被删除。

MCO_E_NOMEM

数据库内存分配错误。

MCO_S_DUPLICATE

尝试在唯一索引中插入重复值。

MCO_ERR_OBJECT_HANDLE

无效的对象句柄。

MCO_ERR_TRN

封闭事务中出现错误。

MCO_ERR_INDEX

插入索引结构时出错。

示例

以下代码片段展示了如何使用 classname_checkpoint() 来更新索引，以便在事务提交之前查找新创建或更新的数据库对象。

    /* 模式文件的片段 */
        
     
    class A {
        uint4 id;
        char<256> name;
 
        tree <id> idx;
    };
     
    /*  应用程序代码片段 */
        
     
    int main(int argc, char* argv[])
    {
         MCO_RET         rc;
        ...
        mco_db_h        db = 0;
        mco_trans_h     t;
        mco_cursor_t    csr;
        A a1, a2;
        A a_out;
        char * name = "Test #N";
        uint4 id = 999;
        uint4 id_out = 0;
        char name_out[64] = "";
                 
        ...
        rc = mco_trans_start(connection, MCO_READ_WRITE, MCO_TRANS_FOREGROUND, &t);
        if ( MCO_S_OK == rc ) 
        {
            // Insert two instances of A
            A_new(t, &a1);
            A_id_put(&a1, id);
            name[6] = '1';
            A_name_put(&a1, name, strlen(name));
            A_new(t, &a2);
            A_id_put(&a2, id + 1);
            name[6] = '2';
            A_name_put(&a2, name, strlen(name));
             
            // Checkpoint to create index entries
            A_checkpoint(&a1);
        
            A_checkpoint(&a2);
        
             
            // Lookup inserted objects by index
            rc = A_idx_index_cursor(t, &csr);
            if (MCO_S_OK == rc)
            {
                printf("\nInside transaction; objects inserted into index: \n");
                for (rc = mco_cursor_first(t, &csr); rc == MCO_S_OK; rc = mco_cursor_next(t, &csr)) 
                {
                    A_from_cursor(t, &csr, &a_out);
                    A_id_get(&a_out, &id_out);
                    A_name_get(&a_out, name_out, sizeof(name_out));
                    printf("\tid=%d, name {%s} \n", id_out, name_out);
                }
            }
            // Rollback the transaction so no inserts are committed
            mco_trans_rollback(t);
        }
         
        // Start a new transaction to check for inserted items
        rc = mco_trans_start(db, MCO_READ_ONLY, MCO_TRANS_FOREGROUND, &t);
        if (MCO_S_OK == rc)
        {
            // Lookup to verify that no objects were inserted - transaction rolled back
            rc = A_idx_index_cursor(t, &csr);
            if (MCO_S_OK == rc)
            {
                printf("\nObjects inserted: \n");
                for (rc = mco_cursor_first(t, &csr); rc == MCO_S_OK; rc = mco_cursor_next(t, &csr))
                {
                    A_from_cursor(t, &csr, &a_out);
                    A_id_get(&a_out, &id_out);
                    A_name_get(&a_out, name_out, sizeof(name_out));
                    printf("\tid=%d, name {%s} \n", id_out, name_out);
                }
            }
            else
            {
                sample_rc_check("\n Attempt to open a cursor after rollback:", rc);
            }
        }
        mco_trans_rollback(t);
        ...
    }