The joiners allows you join two streams yields results if both records in each stream are timely close to each other (i.e., both events happened within a certain time frame).

Base Joiner

The base joiners join both two streams of JSON objects.

Note: If you are using JSON objects without common fields you can use any joiner.

StreamPreferredJoiner

The StreamPreferredJoiner is a joiner that allows us join both two streams of JSON objects, favoring the stream’s fields.

TablePreferredJoiner

The TablePreferredJoiner is a joiner that allows us join both two streams of JSON objects, favoring the table’s fields.

Queryable Joiner

The queryable joiner works like base joiner. The difference is that a queryable joiner will notify to __enricher_queryable topic, if received message cannot be join with other message with same key. We can see two cases:

• CASE 1: Received message cannot be joined with other with same key.

1. Enricher receives a message from stream topic.
2. As there is no any message from table topic, so enricher sends next notification to __enricher_queryable:

    (
      KEY-A,
      {
        "joiner":"joinerStream",
        "type":"joiner-query",
        "table":"metrics",
        "joiner-status":false
      }
    )
   

3. The Unjoined message is sent to output topic.

• CASE 2: Received message can be joined with other with same key.

1. A message is received in table topic.
2. Enricher receives a message from stream topic with same key that message received in table topic.
3. Enricher joins the messages with same key and sends them to output topic:

Just the base joiner, queryable joiner has next functions:

Function	Description
StreamPreferredJoiner	Joiner that allows join both two streams of JSON objects, favoring the stream’s fields.
TablePreferredJoiner	Joiner that allows join both two streams of JSON objects, favoring the tables’s fields.

Queryableback Joiner

The queryableback joiner works like base joiner. The difference is that a queryableback joiner will notify to __enricher_queryable and will resend message to stream, if received message cannot be join with other message with same key.

Image above represents the queryableback join behaviour:

1. Enricher receives a message from stream topic.
2. As there is no any message from table topic, so enricher sends next notification to __enricher_queryable topic:

     (
       KEY-A,
       {
         "joiner":"joinerStream",
         "type":"joiner-query",
         "table":"metrics",
         "joiner-status":false
       }
     )
   

3. Enricher resends the message to stream topic again.
4. Enricher receives the message from table topic.
5. Enricher joins the messages and sends to output topic.

Caution Steps 2 and 3 is a loop, if message isn’t joined then they will be resend forever.

Just as base joiner, queryableback joiner has next functions:

Function	Description
StreamPreferredJoiner	Joiner that allows join both two streams of JSON objects, favoring the stream’s fields.
TablePreferredJoiner	Joiner that allows join both two streams of JSON objects, favoring the tables’s fields.