如何使用 blob 数据类型在 Cassandra 中保存 base64（图像）？

Question

如何使用 blob 数据类型在 Cassandra 中保存 base64(image) ？

这是我的创建表查询：

CREATE TABLE IF NOT EXISTS xadvisor.session ( user_id varchar, images set <blob>, PRIMARY KEY(user_id));

这是我的插入查询：

INSERT INTO xadvisor.session ( user_id , images) VALUES ('XAU1', {\'"+base64+"\'});

base64是从我的本地图片实现的：

var base64 = fs.readFileSync(path.resolve(__dirname + '/../tmp/assets/images_png/capture00001.png'), 'base64');

我收到这样的错误： {"name":"ResponseError","stack":"Error: Invalid set literal for images: value 'iVBORw0KGgoAAAANSUhEUgAABHQAAAHuCAYAAAD+yVs........

提前感谢您的关注和建议:)

Answer 1

在 datastax 的 nodejs 驱动程序中，blob 等于缓冲区，请参见此处： http://datastax.github.io/nodejs-driver/features/datatypes/

但如果您打算使用 base64 - 您只是在处理一些文本，根本不需要使用 blob。

提醒：保持“blob”足够小以提高性能（个位数兆字节）。

更新：哦，我忽略了设置。

您是否遇到任何错误？那么也请提供。

集合在 CQL 中受到限制 - 值必须小于 64kb。 收藏（集）：收藏上限：~20亿（231）；值大小： 65535（216-1）

http://docs.datastax.com/en/cql/3.3/cql/cql_reference/refLimits.html

更新：

typeAsBlob() 可能是你的朋友（见http://docs.datastax.com/en/cql/3.3/cql/cql_reference/blob_r.html）——例如textAsBlob():

cqlsh:demo> DESCRIBE blob ;

CREATE TABLE demo.blob (
    user_id text PRIMARY KEY,
    payload blob
) WITH bloom_filter_fp_chance = 0.01
    AND caching = '{"keys":"ALL", "rows_per_partition":"NONE"}'
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'}
    AND compression = {'sstable_compression': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99.0PERCENTILE';

cqlsh:demo> INSERT INTO blob (user_id, payload) VALUES ('demo_user','YXNsa2RramFzZAo=');
InvalidRequest: Error from server: code=2200 [Invalid query] message="Invalid STRING constant (YXNsa2RramFzZAo=) for "payload" of type blob"
cqlsh:demo> INSERT INTO blob (user_id, payload) VALUES ('demo_user',textAsblob('YXNsa2RramFzZAo='));
cqlsh:demo> SELECT * FROM blob ;

 user_id   | payload
-----------+------------------------------------
 demo_user | 0x59584e7361325272616d467a5a416f3d

(1 rows)
cqlsh:demo>

因为 base64 编码的图像只是一个字符串，您也可以使用文本。为了存储您的图像，构建一个单独的表来保存它们，user_id 作为分区键，唯一标识符（可能是哈希）作为集群列：

cqlsh> USE demo ;
cqlsh:demo> DESCRIBE TABLE demo.images ;

CREATE TABLE demo.images (
    user_id text,
    image_id text,
    image_payload text,
    PRIMARY KEY (user_id, image_id)
) WITH CLUSTERING ORDER BY (image_id ASC)
    AND bloom_filter_fp_chance = 0.01
    AND caching = '{"keys":"ALL", "rows_per_partition":"NONE"}'
    AND comment = ''
    AND compaction = {'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'}
    AND compression = {'sstable_compression': 'org.apache.cassandra.io.compress.LZ4Compressor'}
    AND dclocal_read_repair_chance = 0.1
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99.0PERCENTILE';

cqlsh:demo> INSERT INTO demo.images (user_id, image_id, image_payload) VALUES ('demo_user1', 'img000.png', 'YWRsa2tqYXNkaGpzZAo=');
cqlsh:demo> INSERT INTO demo.images (user_id, image_id, image_payload) VALUES ('demo_user1', 'img002.png', 'YWRsa2tqYXNkaGpzZAo=');
cqlsh:demo> INSERT INTO demo.images (user_id, image_id, image_payload) VALUES ('demo_user1', 'img017.png', 'YWRsa2tqYXNkaGpzZAo=');
cqlsh:demo> INSERT INTO demo.images (user_id, image_id, image_payload) VALUES ('demo_user2', 'img001.png', 'YWRsa2tqYXNkaGpzZAo=');
cqlsh:demo> INSERT INTO demo.images (user_id, image_id, image_payload) VALUES ('demo_user2', 'img002.png', 'YWRsa2tqYXNkaGpzZAo=');
cqlsh:demo> SELECT image_id, image_payload FROM demo.images WHERE user_id = 'demo_user1';

 image_id   | image_payload
------------+----------------------
 img000.png | YWRsa2tqYXNkaGpzZAo=
 img002.png | YWRsa2tqYXNkaGpzZAo=
 img017.png | YWRsa2tqYXNkaGpzZAo=

(3 rows)
cqlsh:demo>