Event Filters

[brianneisler]

This is a Feature Request

Description

Provide a easy way of filtering events. Filters should be configurable and capable of filtering on multiple values.

Use-cases

• Prevent a function from being invoked on every event of a particular type.
• Filter events based on data values.
• Segment events between functions based on data in the event.

Concepts

• Filters are specified using the filters property.
• The filters property is expected to be an array.
• Each filter is a logical statement that is meant to be resolved to a boolean.
• Statements are simple code meant to be compiled to executable functions (some better way?)
• Multiple filters are AND'd together.

Variables

• Each statement has a few predefined variables that are available.

event

• The event variable represents the current event that is being compared.
• All of the event's internal properties are available for comparison
• The data field in the event should be lazily deserialized (if possible)

Literals

false

• represents the boolean primitive false

true

• represents the boolean primitive true

Functions

• Each statement has a few predefined functions that are available.

isString

• determines if the value is a string

isString(event.data.foo)

isNumber

• determines if the value is a number

isNumber(event.data.foo)

isBoolean

• determines if the value is a boolean

isBoolean(event.data.foo)

Operators

• There are several operators that are available for comparison

Operator	Description	Example
==	equality	event.data.foo == 'bar'
!=	inequality	event.data.bar != 'baz'
>	greater than	event.received > 0
>=	greater than or equal
<	less than
<=	less than or equal
&&	and	event.data.a && event.data.b
||	or	event.data.a || event.data.b
!	not	!event.data.val

Examples

1. Filter events based on some data property

Event

{
  "event": "someEventType",
  "id": "66dfc31d-6844-42fd-b1a7-a489a49f65f3",
  "received": 1500897327098,
  "data": "{\"foo\": \"bar\"}",
  "encoding": "json"
}

Subscription that matches event sdk usage

fdk.subscribe("someFunction", {
  event: "someEventType",
  filters: [
    "event.data.foo == 'bar'"
  ]
})

Subscription - framework usage

functions:
  sendEmail:
    handler: index.sendEmail
    events:
      - myapp.user.created:
           filters: 
             - "event.data.validEmail != true"