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redis-tagging v1.4.0

Fast and simple tagging of (sorted) items


Build Status

Fast and simple tagging of (sorted) items.


  • Maintains the order of tagged items with the help of Redis Sorted Sets.
  • Unions and intersections on tags while also maintaining the order.
  • Fast and efficient paging over thousands of results with support of limit, offset.
  • Namespaces to keep multiple "buckets" of tags on the same server.
  • Counters for each tag in a namespace.
  • REST interface via REST Tagging
  • Test coverage

A short example

Tagging and efficient querying of items with unions and intersections is no fun with traditional databases.

Imagine a SQL database with concerts that need to be output ordered by date. Each item is tagged with tags like chicago, rock, stadium, open-air. Now let's try to get the following items:

  • 10 concerts (ordered by date) in chicago (limit=10, tags=["chicago"]) and the total amount of concerts in chicago.
  • The next 10 concerts, skipping the first 10, (limit=10, tags=["chicago"], offset=10) and the total amount.
  • 40 concerts in detroit, chicago or cleveland (limit=40, tags=["detroit", "chicago", "cleveland"], type="union") and the total amount.
  • 50 concerts that are rock and in a stadium (limit=50, tags=["rock", "stadium"]) and the total amount.
  • The top 20 tags used and the amount of items tagged with each.

Those queries together with the maintenance of tables and indexes can be a pain with SQL. Enter Redis and its fast in-memory set opererations.

Fast and efficient tagging

Here is how Redis-Tagging will make the tagging of items in external databases fast and easy:

  • When storing an item in your database you still store the tags but in a normal string field for reference and easy output. You will no longer use this field in a WHERE-statement. No additional tables for tags and tag associations are needed.
  • You post the id, a score (for sorting) and the list of tags to Redis-Tagging whenever you add, update or delete an item. The score could be a date timestamp or any other number you use for sorting.
  • Redis-Tagging will output all results (e.g. all items with tags chicago and rock) as a list of IDs ordered correctly by the score you supplied.
  • You use this list of IDs to get the actual items from your database.

So with little changes you will end up with a lot less code, tables and need to maintain a complex structure just to support fast tagging.

REST interface

If you want to use the REST interface to access Redis Tagging from a non Node.js application please have a look at: REST Tagging


npm i redis-tagging --save


Parameters for RedisTagging:

  • host (String): optional (Default: "") The Redis server
  • port (Number): optional (Default: 6379) The Redis port
  • options, optional Default: {}. Additional options. See:
  • nsprefix (String): optional (Default: "rt") The namespace prefix used for all keys created by Redis Tagging
  • client: optional An external RedisClient object which will be used for the connection.
var RedisTagging = require("redis-tagging");
var rt = new RedisTagging({host: "", port: 6379, nsprefix: "rt"} );

Important: Redis-Tagging works with items from your database (whatever you might use). Its purpose is to make tag based lookups fast and easy.
A typical item in your database should include an id (the primary key) and a list of tags for this items. You could store this as a JSON string (e.g. ["car", "bmw", "suv", "x5"].
You'll want to try to keep your db in sync with the item ids stored in Redis-Tagging.

Go through the following examples to see what Redis-Tagging can do for you:

Set tags for an item

This will create an item with the id itm123.
Note: There is no partial update of tags for an item. You always write the full list of tags.

        bucket: "concerts",
        id: "itm123",
        tags: ["new york", "stadium", "rock", "open-air"],
        score: 1356341337
    function (err, resp) {
        if (resp === true) {
            // item was saved

Get tags for an item

Returns all tags for an item id.

Note: This method is usually not needed if you store the tags for each item in your database.

        bucket: "concerts",
        id: "itm123"
    function (err, resp) {
        // resp countains an array of all tags
        // For the above set example resp will contain:
        // ["new york", "stadium", "rock", "open-air"]

Remove all tags for an item

Note: This is the same as using set with an empty array of tags.

        bucket: "concerts",
        id: "itm123"
    function (err, resp) {
        if (resp === true) {
            // item was removed

Get all item ids in a bucket

        bucket: "concerts"
    function (err, resp) {
        // resp countains an array of all ids

Tags: Query items by tag

The main method. Return the IDs for one or more tags. When more than one tag is supplied the query can be an intersection (default) or a union. type=inter (default) only those IDs will be returned where all tags match. type=union all IDs where any tag matches will be returned.

Parameters object:

  • bucket (String)
  • tags (Array) One or more tags
  • limit (Number) optional Default=100 (0 will return 0 items but will return the total_items!)
  • offset (Number) optional Default=0
  • withscores (Number) optional Default=0 Set this to 1 to output the scores
  • order (String) optional Default ="desc"
  • type (String) optional "inter", "union" Default: "inter"
        bucket: "concerts",
        tags: ["berlin", "rock"],
        limit: 2,
        offset: 4
    function (err, resp) {
        // resp contains:
        //  {"total_items":108,
        //  "items":["8167","25652"],
        //  "limit":2,
        //  "offset":4}

The returned data is item no. 5 and 6. The first 4 got skipped (offset=4). You can now do a

SELECT * FROM Concerts WHERE ID IN (8167,25652) ORDER BY Timestamp DESC

Top Tags

Return the top n tags of a bucket.

        bucket: "concerts",
        amount: 3
    function (err, resp) {
        // resp contains:
        //  {
        //      "total_items": 18374,
        //      "items":[
        //          {"tag":"rock", "count":1720},
        //          {"tag":"pop", "count":1585},
        //          {"tag":"New York", "count":720}
        //      ]
        //  }


List all buckets with at least one item stored in Redis.

Important: This method uses the Redis keys command. Use with care.

    function (err, resp) {
        // resp contains an array with all buckets

Remove a bucket

Removes a single bucket and all items

        bucket: "concerts"
    function (err, resp) {
        if (resp === true) {
            // bucket was removed

How to migrate to Redis-Tagging

  • Make sure your DB has the following fields for the items you want to tag (names don't need to match exactly):
    • id: A primary key to quickly find your item.
    • score: Any number you use to sort your data. This is usually a date. If you saved a date in date-format you need to convert it to a numeric timestamp.
    • tags: A list of tags for this item. It is up to you how you store this. Usually a normal string field is sufficient.
  • Do a set for each item to populate the Redis-Tagging data.
  • When you insert / update / delete items in your DB make sure you also tell Redis-Tagging about it.
  • Now use the methods described above to make intersections and get the IDs back.
  • Use the IDs to get the actual records from your DB and display them as usual.
  • Enjoy.



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