Migrator

Kotlin |Java

abstract class Migrator

kotlin.Any
↳	android.app.appsearch.Migrator

A migrator class to translate GenericDocument from different version of AppSearchSchema

Make non-backwards-compatible changes will delete all stored documents in old schema. You can save your documents by setting Migrator via the android.app.appsearch.SetSchemaRequest.Builder#setMigrator for each type and target version you want to save.

onDowngrade or onUpgrade will be triggered if the version number of the schema stored in AppSearch is different with the version in the request.

If any error or Exception occurred in the onDowngrade or onUpgrade, all the setSchema request will be rejected unless the schema changes are backwards-compatible, and stored documents won't have any observable changes.

Summary

Public constructors
`Migrator()`

Public methods
abstract GenericDocument	`onDowngrade(currentVersion: Int, finalVersion: Int, document: GenericDocument)` Migrates `GenericDocument` to an older version of `AppSearchSchema`.
abstract GenericDocument	`onUpgrade(currentVersion: Int, finalVersion: Int, document: GenericDocument)` Migrates `GenericDocument` to a newer version of `AppSearchSchema`.
abstract Boolean	`shouldMigrate(currentVersion: Int, finalVersion: Int)` Returns `true` if this migrator's source type needs to be migrated to update from currentVersion to finalVersion.

Public constructors

Migrator

Added in API level 31

Migrator()

Public methods

onDowngrade

Added in API level 31

abstract fun onDowngrade(
    currentVersion: Int, 
    finalVersion: Int, 
    document: GenericDocument
): GenericDocument

Migrates GenericDocument to an older version of AppSearchSchema.

This method will be invoked only if the SetSchemaRequest is setting a lower version number than the current AppSearchSchema saved in AppSearch.

If this Migrator is provided to cover a compatible schema change via android.app.appsearch.AppSearchSession#setSchema, documents under the old version won't be removed unless you use the same document ID.

This method will be invoked on the background worker thread.
This method may take several seconds to complete, so it should only be called from a worker thread.

Parameters
`currentVersion`	Int: The current version of the document's schema.
`finalVersion`	Int: The final version that documents need to be migrated to.
`document`	GenericDocument: The `GenericDocument` need to be translated to new version. This value cannot be `null`.

Return
`GenericDocument`	A `GenericDocument` in new version. This value cannot be `null`.

onUpgrade

Added in API level 31

abstract fun onUpgrade(
    currentVersion: Int, 
    finalVersion: Int, 
    document: GenericDocument
): GenericDocument

Migrates GenericDocument to a newer version of AppSearchSchema.

This method will be invoked only if the SetSchemaRequest is setting a higher version number than the current AppSearchSchema saved in AppSearch.

This method will be invoked on the background worker thread provided via android.app.appsearch.AppSearchSession#setSchema.
This method may take several seconds to complete, so it should only be called from a worker thread.

Parameters
`currentVersion`	Int: The current version of the document's schema.
`finalVersion`	Int: The final version that documents need to be migrated to.
`document`	GenericDocument: The `GenericDocument` need to be translated to new version. This value cannot be `null`.

Return
`GenericDocument`	A `GenericDocument` in new version. This value cannot be `null`.

shouldMigrate

Added in API level 31

abstract fun shouldMigrate(
    currentVersion: Int, 
    finalVersion: Int
): Boolean

Returns true if this migrator's source type needs to be migrated to update from currentVersion to finalVersion.

Migration won't be triggered if currentVersion is equal to finalVersion even if shouldMigrate return true;