UDA自定义函数

结构定义

在调用 mco_uda_register_udf() 时需要一个类型为 mco_uda_userdef_funcs_t 的结构体。其在 mcouda.h 中的定义如下：

    typedef struct mco_uda_userdef_funcs_t_ {
        mco_uda_compare_userdef_f         fcomp;
        mco_uda_compare_extkey_userdef_f  fcomp_ext;
        mco_uda_hash_userdef_f            fhash;
        mco_uda_hash_extkey_userdef_f     fhash_ext;
    } mco_uda_userdef_funcs_t, *mco_uda_userdef_funcs_h;

UDA 用户定义函数对于从 UDA 函数中调用的用户定义索引是必需的。它们在 mcouda.h 中定义了以下原型：

    typedef int2 (*mco_uda_compare_userdef_f)(
        mco_uda_object_handle_p obj1, 
        unsigned short index1, 
        mco_uda_object_handle_p obj2, 
        unsigned short index2, 
        void *user_context
    );
             
    typedef int2 (*mco_uda_compare_extkey_userdef_f)(
        mco_uda_object_handle_p obj, 
        unsigned short index,
        mco_uda_value_t *keys, 
        uint2 keys_count, 
        void *user_context
    );
             
    typedef uint4 (*mco_uda_hash_userdef_f)(
        mco_uda_object_handle_p obj, 
        unsigned short index, 
        void *user_context
    );
     
    typedef uint4 (*mco_uda_hash_extkey_userdef_f)(
        mco_uda_value_t *keys, 
        uint2 keys_count, 
        void *user_context
    );

请注意，比较函数应根据对象值是否小于、等于或大于外部键值分别返回 <0、= 或 >0。以下是 UDA 用户定义函数实现的示例：

    /* 用户自定义的比较和哈希函数 */
    int2 cmp_obj_obj(mco_uda_object_handle_p obj1, unsigned short index1, 
        mco_uda_object_handle_p obj2, unsigned short index2, void *param_)
    {
        mco_uda_value_t val1, val2;
        char buf1[20], buf2[20];
        userdef_param_t *param = (userdef_param_t *) param_; /* Get context */

        /* 获取第一个对象的值 */
        val1.type = MCO_DD_STRING;
        val1.v.p.size = sizeof(buf1);
        val1.v.p.p.c = buf1;
        mco_uda_get(obj1, param->fld_no, index1, &val1);
        /* 获取第二个对象的值 */
        val2.type = MCO_DD_STRING;
        val2.v.p.size = sizeof(buf2);
        val2.v.p.p.c = buf2;
        mco_uda_get(obj2, param->fld_no, index2, &val2);

        /* 比较数值 */
        return STR_CMP(buf1, buf2);
    }

    int2 cmp_obj_ext(mco_uda_object_handle_p obj, unsigned short index, 
        mco_uda_value_t *keys, uint2 keys_count, void *param_)
    {
        mco_uda_value_t val;
        char buf[20];
        userdef_param_t *param = (userdef_param_t *) param_;

        /* 获取对象的值 */
        val.type = MCO_DD_STRING;
        val.v.p.size = sizeof(buf);
        val.v.p.p.c = buf;
        mco_uda_get(obj, param->fld_no, index, &val);

        /* 比较对象的值和外部键 */
        return STR_CMP(buf, keys[0].v.p.p.c);
    }

    uint4 hash_obj(mco_uda_object_handle_p obj, unsigned short index, void *param_)
    {
        mco_uda_value_t val;
        char buf[20];
        userdef_param_t *param = (userdef_param_t *) param_;

        /* 获取对象的值 */
        val.type = MCO_DD_STRING; 
        val.v.p.size = sizeof(buf);
        val.v.p.p.c = buf;
        mco_uda_get(obj, param->fld_no, index, &val);

        /* 哈希值 */
        return strlen(buf);
    }

    uint4 hash_ext(mco_uda_value_t *keys, uint2 keys_count, void *param)
    {
        /* 哈希外键 */
        return strlen(keys[0].v.p.p.c);
    }