PersistDataValue

The PersistDataValue transformation stores a value from the dispatch payload (or a constant) into the data layer with a configurable expiry and update policy. On the same dispatch, the effectively persisted value is also injected back into the payload so it is immediately available downstream. If the persistence fails or the update policy prevents the write, the dispatch is returned unchanged.

Requires: TealiumPrismExtensions

Registration

The PersistDataValue transformer is registered automatically when the TealiumPrismExtensions library is linked to your app (via the Objective-C +load mechanism). No additional setup is required.

Programmatic Configuration

Use PersistDataValueSettingsBuilder to configure the transformation:

// Persist a payload value to the data layer (session-scoped by default)
let persistUserId = PersistDataValueSettingsBuilder(id: "persist-user-id")
    .persistFrom(.key("user_id"), to: .key("persisted_user_id"))
    .setScope(.dispatchers(["Analytics", "Collect"]))
    .setOrder(1)

config.setTransformation(persistUserId)

// Persist a constant value, never expire it, and never overwrite once set
let persistAppVersion = PersistDataValueSettingsBuilder(id: "persist-app-version")
    .persistConstant("2.4.0", to: .key("first_seen_version"))
    .setExpiryPolicy(.forever)
    .setUpdatePolicy(.keepFirstValue)
    .setScope(.afterCollectors)
    .setOrder(1)

config.setTransformation(persistAppVersion)

// Persist for a custom duration
let persistCampaign = PersistDataValueSettingsBuilder(id: "persist-campaign")
    .persistFrom(.key("utm_campaign"), to: .key("last_campaign"))
    .setExpiryPolicy(.duration(30.days))
    .setScope(.afterCollectors)
    .setOrder(1)

config.setTransformation(persistCampaign)

Builder methods:

Method	Description
`persistConstant(_:to:)`	Persist a constant value
`persistFrom(_:to:)`	Persist the value found at `input` in the dispatch payload
`setExpiryPolicy(_:)`	How long the data layer value lives. Default: `.session`
`setUpdatePolicy(_:)`	Whether subsequent writes can overwrite the stored value. Default: `.allowUpdate`

ExpiryPolicy options:

Value	Description
`.session`	Cleared when the session ends (default)
`.untilRestart`	Cleared on the next app launch
`.forever`	Never expires
`.duration(TimeFrame)`	Expires after the given time frame

UpdatePolicy options:

Value	Description
`.allowUpdate`	Subsequent persists overwrite the stored value (default)
`.keepFirstValue`	The first successfully written value is preserved; later writes are ignored

JSON Configuration

{
  "transformation_id": "persist-user-id",
  "transformer_id": "PersistDataValue",
  "scope": ["Analytics", "Collect"],
  "order": 1,
  "configuration": {
    "input": { "key": "user_id" },
    "destination": { "key": "persisted_user_id" },
    "duration": -2,
    "update_policy": "allowUpdate"
  }
}

duration encoding:

Value	Meaning
`-1`	`.forever`
`-2`	`.session`
`-3`	`.untilRestart`
`>= 0`	Seconds until expiry (`.duration`)

update_policy values: "allowUpdate" or "keepFirstValue" (case-insensitive).

Constant input:

{
  "configuration": {
    "input": { "value": "2.4.0" },
    "destination": { "key": "first_seen_version" },
    "duration": -1,
    "update_policy": "keepFirstValue"
  }
}