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‎src/content/docs/durable-objects/reference/durable-objects-migrations.mdx‎

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title: Durable Objects migrations
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sidebar:
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order: 2
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---
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import { GlossaryTooltip, WranglerConfig, Steps, Details } from "~/components";
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A migration is a mapping process from a class name to a runtime state. This process communicates the changes to the Workers runtime and provides the runtime with instructions on how to deal with those changes.
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---
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To apply a migration, you need to:
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import { GlossaryTooltip, WranglerConfig } from "~/components";
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1. Edit your `wrangler.toml / wrangler.json` file, as explained below.
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2. Re-deploy your Worker using `npx wrangler deploy`.
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A migration is a mapping process from a class name to a runtime state.
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You must initiate a migration process when you:
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- Create a new <GlossaryTooltip term="Durable Object class">Durable Object class</GlossaryTooltip>.
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- Rename a Durable Object class.
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- Delete a Durable Object class.
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- Transfer an existing Durable Objects class.
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:::note
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Updating the code for an existing Durable Object class does not require a migration. To update the code for an existing Durable Object class, run [`npx wrangler deploy`](/workers/wrangler/commands/#deploy). This is true even for changes to how the code interacts with persistent storage. Because of [global uniqueness](/durable-objects/platform/known-issues/#global-uniqueness), you do not have to be concerned about old and new code interacting with the same storage simultaneously. However, it is your responsibility to ensure that the new code is backwards compatible with existing stored data.
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:::
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## Create migration
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The most common migration performed is a new class migration, which informs the runtime that a new Durable Object class is being uploaded. This is also the migration you need when creating your first Durable Object class.
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* Create a new <GlossaryTooltip term="Durable Object class">Durable Object class</GlossaryTooltip>.
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* Rename a Durable Object class.
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* Delete a Durable Object class.
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* Transfer an existing Durable Objects class.
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To apply a Create migration:
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This process informs the Workers runtime of the changes and provides it with instructions on how to deal with those changes.
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<Steps>
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1. Add the following lines to your `wrangler.toml / wrangler.json` file:
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:::note
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<WranglerConfig>
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```toml
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[[migrations]]
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tag = "<v1>" # Migration identifier. This should be unique for each migration entry
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new_classes = ["<NewDurableObjectClass>"] # Array of new classes
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# For SQLite storage backend use new_sqlite_classes=["<NewDurableObjectClass>"] instead
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```
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</WranglerConfig>
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The Create migration contains:
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- A `tag` to identify the migration.
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- The array `new_classes`, which contains the new Durable Object class.
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Updating code for an existing Durable Object class does not require a migration. To update code for an existing Durable Object class, run [`npx wrangler deploy`](/workers/wrangler/commands/#deploy). This is true even for changes to how code interacts with persistent storage. Because of [global uniqueness](/durable-objects/platform/known-issues/#global-uniqueness), you do not have to be concerned about old and new code interacting with the same storage simultaneously. However, it is your responsibility to ensure that new code is backwards compatible with existing stored data.
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2. Ensure you reference the correct name of the Durable Object class in your Worker code.
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3. Deploy the Worker.
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</Steps>
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<Details header="Create migration example">
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:::
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To create a new Durable Object binding `DURABLE_OBJECT_A`, your `wrangler.toml / wrangler.json` file should look like the following:
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The most common migration performed is a new class migration, which informs the runtime that a new Durable Object class is being uploaded.
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<WranglerConfig>
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```toml
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# Creating a new Durable Object class
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[[durable_objects.bindings]]
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name = "DURABLE_OBJECT_A"
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class_name = "DurableObjectAClass"
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Migrations can also be used for transferring stored data between two Durable Object classes:
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# Add the lines below for a Create migration.
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[[migrations]]
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tag = "v1"
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new_classes = ["DurableObjectAClass"]
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```
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</WranglerConfig>
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* Rename migrations are used to transfer stored Durable Objects between two Durable Object classes in the same Worker code file.
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* Transfer migrations are used to transfer stored Durable Objects between two Durable Object classes in different Worker code files.
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</Details>
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The destination class (the class that stored Durable Objects are being transferred to) for a rename or transfer migration must be exported by the deployed Worker.
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## Delete migration
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:::caution[Important]
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Running a Delete migration will delete all Durable Objects associated with the deleted class, including all of their stored data.
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- Do not run a Delete migration on a class without first ensuring that you are not relying on the Durable Objects within that Worker anymore, that is, first remove the binding from the Worker.
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- Copy any important data to some other location before deleting.
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- You do not have to run a Delete migration on a class that was renamed or transferred.
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After a rename or transfer migration, requests to the destination Durable Object class will have access to the source Durable Object's stored data.
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To apply a Delete migration:
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After a migration, any existing bindings to the original Durable Object class (for example, from other Workers) will automatically forward to the updated destination class. However, any Workers bound to the updated Durable Object class must update their Durable Object binding configuration in the Wrangler file for their next deployment.
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<Steps>
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1. Remove the binding for the class you wish to delete from the `wrangler.toml / wrangler.json` file.
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2. Remove references for the class you wish to delete from your Worker code.
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3. Add the following lines to your `wrangler.toml / wrangler.json` file.
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<WranglerConfig>
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```toml
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[[migrations]]
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tag = "<v2>" # Migration identifier. This should be unique for each migration entry
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deleted_classes = ["<ClassToDelete>"] # Array of deleted class names
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```
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</WranglerConfig>
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The Delete migration contains:
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:::
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- A `tag` to identify the migration.
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- The array `deleted_classes`, which contains the deleted Durable Object classes.
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4. Deploy the Worker.
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</Steps>
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Migrations can also be used to delete a Durable Object class and its stored Durable Objects.
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<Details header = "Delete migration example">
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To delete a Durable Object binding `DEPRECATED_OBJECT`, your `wrangler.toml / wrangler.json` file should look like the following:
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:::caution[Delete migrations]
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<WranglerConfig>
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```toml
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# Remove the binding for the DeprecatedObjectClass DO
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#[[durable_objects.bindings]]
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#name = "DEPRECATED_OBJECT"
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#class_name = "DeprecatedObjectClass"
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[[migrations]]
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tag = "v3" # Should be unique for each entry
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deleted_classes = ["DeprecatedObjectClass"] # Array of new classes
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```
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</WranglerConfig>
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</Details>
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Running a delete migration will delete all Durable Objects associated with the deleted class, including all of their stored data. Do not run a delete migration on a class without first ensuring that you are not relying on the Durable Objects within that class anymore. Copy any important data to some other location before deleting.
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## Rename migration
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Rename migrations are used to transfer stored Durable Objects between two Durable Object classes in the same Worker code file.
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:::
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To apply a Rename migration:
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### Durable Object migrations in the Wrangler configuration file
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<Steps>
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1. Update the previous class name to the new class name by editing your `wrangler.toml / wrangler.json` file in the following way:
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Migrations are performed through the `[[migrations]]` configurations key in your Wrangler file.
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<WranglerConfig>
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```toml
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[[durable_objects.bindings]]
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name = "<MY_DURABLE_OBJECT>"
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class_name = "<UpdatedDurableObject>" # Update the class name to the new class name
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Migrations require a migration tag, which is defined by the `tag` property in each migration entry.
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[[migrations]]
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tag = "<v3>" # Migration identifier. This should be unique for each migration entry
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renamed_classes = [{from = "<OldDurableObject>", to = "<UpdatedDurableObject>" }] # Array of rename directives
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```
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</WranglerConfig>
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Migration tags are treated like unique names and are used to determine which migrations have already been applied. Once a given Worker code has a migration tag set on it, all future Worker code deployments must include a migration tag.
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The Rename migration contains:
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- A `tag` to identify the migration.
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- The `renamed_classes` array, which contains objects with `from` and `to` properties.
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- `from` property is the old Durable Object class name.
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- `to` property is the renamed Durable Object class name.
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2. Reference the new Durable Object class name in your Worker code.
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3. Deploy the Worker.
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</Steps>
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The migration list is an ordered array of tables, specified as a top-level key in your Wrangler file. The migration list is inherited by all environments and cannot be overridden by a specific environment.
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<Details header = "Rename migration example">
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All migrations are applied at deployment. Each migration can only be applied once per [environment](/durable-objects/reference/environments/).
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To rename a Durable Object class, from `OldName` to `UpdatedName`, your `wrangler.toml / wrangler.json` file should look like the following:
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To illustrate an example migrations workflow, the `DurableObjectExample` class can be initially defined with:
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<WranglerConfig>
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```toml
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# Before deleting the `DeprecatedClass` remove the binding for the `DeprecatedClass`.
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# Update the binding for the `DurableObjectExample` to the new class name `UpdatedName`.
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[[durable_objects.bindings]]
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name = "MY_DURABLE_OBJECT"
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class_name = "UpdatedName"
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# Renaming classes
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```toml
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[[migrations]]
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tag = "v3"
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renamed_classes = [{from = "OldName", to = "UpdatedName" }] # Array of rename directives
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tag = "v1" # Should be unique for each entry
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new_classes = ["DurableObjectExample"] # Array of new classes
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```
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</WranglerConfig>
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</Details>
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## Transfer migration
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Transfer migrations are used to transfer stored Durable Objects between two Durable Object classes in different Worker code files.
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If you want to transfer stored Durable Objects between two Durable Object classes in the same Worker code file, use [Rename migrations](#rename-migration) instead.
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:::note
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Do not run a [Create migration](#create-migration) for the destination class before running a Transfer migration. The Transfer migration will create the destination class for you.
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:::
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To apply a Transfer migration:
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<Steps>
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1. Edit your `wrangler.toml / wrangler.json` file in the following way:
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<WranglerConfig>
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```toml
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[[durable_objects.bindings]]
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name = "<MY_DURABLE_OBJECT>"
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class_name = "<DestinationDurableObjectClass>"
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</WranglerConfig>
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[[migrations]]
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tag = "<v4>" # Migration identifier. This should be unique for each migration entry
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transferred_classes = [{from = "<SourceDurableObjectClass>", from_script = "<SourceWorkerScript>", to = "<DestinationDurableObjectClass>" }]
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```
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</WranglerConfig>
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The Transfer migration contains:
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- A `tag` to identify the migration.
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- The `transferred_class` array, which contains objects with `from`, `from_script`, and `to` properties.
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- `from` property is the name of the source Durable Object class.
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- `from_script` property is the name of the source Worker script.
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- `to` property is the name of the destination Durable Object class.
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2. Ensure you reference the name of the new, destination Durable Object class in your Worker code.
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3. Deploy the Worker.
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</Steps>
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Each migration in the list can have multiple directives, and multiple migrations can be specified as your project grows in complexity. For example, you may want to rename the `DurableObjectExample` class to `UpdatedName` and delete an outdated `DeprecatedClass` entirely.
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<Details header = "Transfer migration example">
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You can transfer stored Durable Objects from `DurableObjectExample` to `TransferredClass` from a Worker script named `OldWorkerScript`. The configuration of the `wrangler.toml / wrangler.json` file for your new Worker code (destination Worker code) would look like this:
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<WranglerConfig>
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```toml
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# destination worker
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[[durable_objects.bindings]]
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name = "MY_DURABLE_OBJECT"
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class_name = "TransferredClass"
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[[migrations]]
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tag = "v1" # Should be unique for each entry
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new_classes = ["DurableObjectExample"] # Array of new classes
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# Transferring class
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[[migrations]]
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tag = "v4"
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transferred_classes = [{from = "DurableObjectExample", from_script = "OldWorkerScript", to = "TransferredClass" }]
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tag = "v2"
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renamed_classes = [{from = "DurableObjectExample", to = "UpdatedName" }] # Array of rename directives
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deleted_classes = ["DeprecatedClass"] # Array of deleted class names
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```
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</WranglerConfig>
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</Details>
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## Migration Wrangler configuration
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- Migrations are performed through the `[[migrations]]` configurations key in your `wrangler.toml` file or `migration` key in your `wrangler.json` file.
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- Migrations require a migration tag, which is defined by the `tag` property in each migration entry.
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- Migration tags are treated like unique names and are used to determine which migrations have already been applied. Once a given Worker code has a migration tag set on it, all future Worker code deployments must include a migration tag.
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- The migration list is an ordered array of tables, specified as a top-level key in your `wrangler` configuration file. The migration list is inherited by all environments and cannot be overridden by a specific environment.
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- All migrations are applied at deployment. Each migration can only be applied once per [environment](/durable-objects/reference/environments/).
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- Each migration in the list can have multiple directives, and multiple migrations can be specified as your project grows in complexity.
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:::caution[Important]
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- The destination class (the class that stored Durable Objects are being transferred to) for a Rename or Transfer migration must be exported by the deployed Worker.
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- You should not create the destination Durable Object class before running a Rename or Transfer migration. The migration will create the destination class for you.
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- After a Rename or Transfer migration, requests to the destination Durable Object class will have access to the source Durable Object's stored data.
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- After a migration, any existing bindings to the original Durable Object class (for example, from other Workers) will automatically forward to the updated destination class. However, any Workers bound to the updated Durable Object class must update their Durable Object binding configuration in the `wrangler` configuration file for their next deployment.
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:::
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</WranglerConfig>
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:::note
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Note that `.toml` files do not allow line breaks in inline tables (the `{key = "value"}` syntax), but line breaks in the surrounding inline array are acceptable.
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:::
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{/* ## Examples of Durable Object migration
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To illustrate an example migrations workflow, the `DurableObjectExample` class can be initially defined with:
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<WranglerConfig>
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```toml
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# Creating a new Durable Object class
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[[migrations]]
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tag = "v1" # Migration identifier. This should be unique for each migration entry
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new_classes = ["DurableObjectExample"] # Array of new classes
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```
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Note that `.toml` files do not allow line breaks in inline tables (the `{key = "value"}` syntax), but line breaks in the surrounding inline array are acceptable.
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</WranglerConfig>
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You can rename the `DurableObjectExample` class to `UpdatedName` and delete an outdated `DeprecatedClass` entirely. You can create separate migrations for each operation, or combine them into a single migration as shown below. */}
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:::
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## Enable SQLite storage backend on new Durable Object class migration
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### Enable SQLite storage backend on new Durable Object class migration
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:::note[SQLite in Durable Objects Beta]
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The new beta version of Durable Objects is available where each Durable Object has a private, embedded SQLite database. When deploying a new Durable Object class, users can opt-in to a SQLite storage backend in order to access new [SQL API](/durable-objects/api/sql-storage/#exec). Otherwise, a Durable Object class has a key-value storage backend.
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:::
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To allow a new Durable Object class to use a SQLite storage backend, use `new_sqlite_classes` on the migration in your Worker's `wrangler` configuration file:
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To allow a new Durable Object class to use a SQLite storage backend, use `new_sqlite_classes` on the migration in your Worker's Wrangler file:
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<WranglerConfig>
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</WranglerConfig>
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For an example of a new class migration, refer to [Get started: Configure Durable Object class with SQLite storage backend](/durable-objects/get-started/tutorial-with-sql-api/#6-configure-durable-object-class-with-sqlite-storage-backend).
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You cannot enable a SQLite storage backend on an existing, deployed Durable Object class, so setting `new_sqlite_classes` on later migrations will fail with an error. Automatic migration of deployed classes from their key-value storage backend to SQLite storage backend will be available in the future.

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