# androidx.room.migration

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Common/AllAndroid/JVMNative/C/iOS

## Interfaces

|---|---|---|
| `https://developer.android.com/reference/kotlin/androidx/room/migration/AutoMigrationSpec` | Interface for defining an automatic migration specification for Room databases. | Cmn android N |

## Classes

|---|---|---|
| `https://developer.android.com/reference/kotlin/androidx/room/migration/Migration` | Base class for a database migration. | Cmn android N |

## Top-level functions summary

|---|---|---|
| `https://developer.android.com/reference/kotlin/androidx/room/migration/Migration` | `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)( startVersion: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/index.html, endVersion: https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/index.html, migrate: (https://developer.android.com/reference/kotlin/androidx/sqlite/db/SupportSQLiteDatabase) -> https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html )` Creates `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` from `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` to `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` that runs `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` to perform the necessary migrations. | android |

## Top-level functions

### Migration

android Artifact: [androidx.room:room-runtime](https://developer.android.com/jetpack/androidx/releases/room) [View Source](https://cs.android.com/search?q=file:androidx/room/migration/Migration.android.kt+function:Migration) Added in [2.7.0](https://developer.android.com/jetpack/androidx/releases/room#2.7.0)

```
fun Migration(
    startVersion: Int,
    endVersion: Int,
    migrate: (SupportSQLiteDatabase) -> Unit
): Migration
```

Creates `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` from `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` to `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` that runs `https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` to perform the necessary migrations.

A migration can handle more than 1 version (e.g. if you have a faster path to choose when going version 3 to 5 without going to version 4). If Room opens a database at version 3 and latest version is \< 5, Room will use the migration object that can migrate from 3 to 5 instead of 3 to 4 and 4 to 5.

If there are not enough migrations provided to move from the current version to the latest version, Room will clear the database and recreate so even if you have no changes between 2 versions, you should still provide a Migration object to the builder.

`https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` cannot access any generated Dao in this method.

`https://developer.android.com/reference/kotlin/androidx/room/migration/package-summary#Migration(kotlin.Int,kotlin.Int,kotlin.Function1)` is already called inside a transaction and that transaction might actually be a composite transaction of all necessary `Migration`s.