FlashDB/docs/sample-kvdb-type-blob.md

blob type KV example

This example mainly demonstrates the related functions of blob KV. Blob KV is a more commonly used type, and its value is a binary type without type restrictions. Functionally, blob KV is also compatible with string KV. In the use of API, blob KV has a set of independent APIs, which can quickly realize the storage of various types of KV to KVDB, such as basic types, arrays and structures.

Code description

The sample code is located in samples/kvdb_type_blob.c, and a KV named "temp" is used to store the temperature value, respectively demonstrating the whole process of blob KV from create->read->modify->delete. The general content is as follows:

void kvdb_type_blob_sample(fdb_kvdb_t kvdb)
{
    struct fdb_blob blob;

    FDB_INFO("==================== kvdb_type_blob_sample ====================\n");

    { /* CREATE new Key-Value */
        int temp_data = 36;

        /* It will create new KV node when "temp" KV not in database.
         * fdb_blob_make: It's a blob make function, and it will return the blob when make finish.
         */
        fdb_kv_set_blob(kvdb, "temp", fdb_blob_make(&blob, &temp_data, sizeof(temp_data)));
        FDB_INFO("create the 'temp' blob KV, value is: %d\n", temp_data);
    }

    { /* GET the KV value */
        int temp_data = 0;

        /* get the "temp" KV value */
        fdb_kv_get_blob(kvdb, "temp", fdb_blob_make(&blob, &temp_data, sizeof(temp_data)));
        /* the blob.saved.len is more than 0 when get the value successful */
        if (blob.saved.len > 0) {
            FDB_INFO("get the 'temp' value is: %d\n", temp_data);
        }
    }

    { /* CHANGE the KV value */
        int temp_data = 38;

        /* change the "temp" KV's value to 38 */
        fdb_kv_set_blob(kvdb, "temp", fdb_blob_make(&blob, &temp_data, sizeof(temp_data)));
        FDB_INFO("set 'temp' value to %d\n", temp_data);
    }

    { /* DELETE the KV by name */
        fdb_kv_del(kvdb, "temp");
        FDB_INFO("delete the 'temp' finish\n");
    }

    FDB_INFO("===========================================================\n");
}

Running log

It can be seen from the log:

• First create a KV named "temp" and give the initial value 36℃
• Read the current value of "temp" KV and find that it is the same as the initial value
• Modify the value of "temp" KV to 38℃
• Finally delete "temp" KV

[FlashDB][sample][kvdb][blob] ==================== kvdb_type_blob_sample ====================
[FlashDB][sample][kvdb][blob] create the 'temp' blob KV, value is: 36
[FlashDB][sample][kvdb][blob] get the 'temp' value is: 36
[FlashDB][sample][kvdb][blob] set 'temp' value to 38
[FlashDB][sample][kvdb][blob] delete the 'temp' finish
[FlashDB][sample][kvdb][blob] ===========================================================