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What is a Trigger?

The new data pushed to subscription on receiving the new block in the real time database assuming that the criteria, defined in the query are met:

  • trigger_on attribute matches the block
  • conditions defined in the query matches this block
  • data filtered by all provided conditions, are not empty

trigger_on​

trigger_on attribute controls on which blocks the update of data is triggered for the subscription. It has the following options:

  • all - any block triggers data update
  • head - new blocks on the trunk (with the highest tip) triggers data update
  • head_updates - any blocks on the trunk (with the highest tip) triggers data update
  • branches_updates - any blocks on the branch (not with the highest tip) triggers data update

Blockchain Reorg Tree describes how the tree is represented in the databases.

In most cases you just not specify this attribute, assuming all option is what you need. Other options are suitable for event-driven applications:

tip

Use head_updates together with branches_updates when you need to accumulate all branches and the trunk

tip

Use head if you need to listen only head blocks in your application. This can slightly delay the data however, as the new block may need the other block to wait to be detected that it is on the tree.