📄 tanstack/db/latest/docs/reference/interfaces/LocalOnlyCollectionConfig

File: LocalOnlyCollectionConfig.md | Updated: 11/15/2025

Source: https://tanstack.com/db/latest/docs/reference/interfaces/LocalOnlyCollectionConfig



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LocalOnlyCollectionConfig

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Interface: LocalOnlyCollectionConfig<T, TSchema, TKey>
======================================================

Defined in: packages/db/src/local-only.ts:22

Configuration interface for Local-only collection options

Extends
-------

Type Parameters
--------------- ### T

T extends object = object

The type of items in the collection

### TSchema

TSchema extends StandardSchemaV1 = never

The schema type for validation

### TKey

TKey extends string | number = string | number

The type of the key returned by getKey

Properties
---------- ### autoIndex?

ts

optional autoIndex: "eager" | "off";


optional autoIndex: "eager" | "off";

Defined in: packages/db/src/types.ts:465

Auto-indexing mode for the collection. When enabled, indexes will be automatically created for simple where expressions.

#### Default

ts

"eager"


"eager"

#### Description

  • "off": No automatic indexing
  • "eager": Automatically create indexes for simple where expressions in subscribeChanges (default)

#### Inherited from

BaseCollectionConfig .autoIndex

### compare()?

ts

optional compare: (x, y) => number;


optional compare: (x, y) => number;

Defined in: packages/db/src/types.ts:476

Optional function to compare two items. This is used to order the items in the collection.

#### Parameters ##### x

T

The first item to compare

##### y

T

The second item to compare

#### Returns

number

A number indicating the order of the items

#### Example

ts

// For a collection with a 'createdAt' field
compare: (x, y) => x.createdAt.getTime() - y.createdAt.getTime()


// For a collection with a 'createdAt' field
compare: (x, y) => x.createdAt.getTime() - y.createdAt.getTime()

#### Inherited from

ts

Omit.compare


Omit.compare

### defaultStringCollation?

ts

optional defaultStringCollation: StringCollationConfig;


optional defaultStringCollation: StringCollationConfig;

Defined in: packages/db/src/types.ts:622

Specifies how to compare data in the collection. This should be configured to match data ordering on the backend. E.g., when using the Electric DB collection these options should match the database's collation settings.

#### Inherited from

ts

Omit.defaultStringCollation


Omit.defaultStringCollation

### getKey()

ts

getKey: (item) => TKey;


getKey: (item) => TKey;

Defined in: packages/db/src/types.ts:440

Function to extract the ID from an object This is required for update/delete operations which now only accept IDs

#### Parameters ##### item

T

The item to extract the ID from

#### Returns

TKey

The ID string for the item

#### Example

ts

// For a collection with a 'uuid' field as the primary key
getKey: (item) => item.uuid


// For a collection with a 'uuid' field as the primary key
getKey: (item) => item.uuid

#### Inherited from

ts

Omit.getKey


Omit.getKey

### id?

ts

optional id: string;


optional id: string;

Defined in: packages/db/src/types.ts:429

#### Inherited from

BaseCollectionConfig .id

### initialData?

ts

optional initialData: T[];


optional initialData: T[];

Defined in: packages/db/src/local-only.ts:34

Optional initial data to populate the collection with on creation This data will be applied during the initial sync process

### onDelete?

ts

optional onDelete: DeleteMutationFn<T, TKey, LocalOnlyCollectionUtils, any>;


optional onDelete: DeleteMutationFn<T, TKey, LocalOnlyCollectionUtils, any>;

Defined in: packages/db/src/types.ts:614

Optional asynchronous handler function called before a delete operation

#### Param

Object containing transaction and collection information

#### Returns

Promise resolving to any value

#### Examples

ts

// Basic delete handler
onDelete: async ({ transaction, collection }) => {
  const deletedKey = transaction.mutations[0].key
  await api.deleteTodo(deletedKey)
}


// Basic delete handler
onDelete: async ({ transaction, collection }) => {
  const deletedKey = transaction.mutations[0].key
  await api.deleteTodo(deletedKey)
}

ts

// Delete handler with multiple items
onDelete: async ({ transaction, collection }) => {
  const keysToDelete = transaction.mutations.map(m => m.key)
  await api.deleteTodos(keysToDelete)
}


// Delete handler with multiple items
onDelete: async ({ transaction, collection }) => {
  const keysToDelete = transaction.mutations.map(m => m.key)
  await api.deleteTodos(keysToDelete)
}

ts

// Delete handler with confirmation
onDelete: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  const shouldDelete = await confirmDeletion(mutation.original)
  if (!shouldDelete) {
    throw new Error('Delete cancelled by user')
  }
  await api.deleteTodo(mutation.original.id)
}


// Delete handler with confirmation
onDelete: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  const shouldDelete = await confirmDeletion(mutation.original)
  if (!shouldDelete) {
    throw new Error('Delete cancelled by user')
  }
  await api.deleteTodo(mutation.original.id)
}

ts

// Delete handler with optimistic rollback
onDelete: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  try {
    await api.deleteTodo(mutation.original.id)
  } catch (error) {
    // Transaction will automatically rollback optimistic changes
    console.error('Delete failed, rolling back:', error)
    throw error
  }
}


// Delete handler with optimistic rollback
onDelete: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  try {
    await api.deleteTodo(mutation.original.id)
  } catch (error) {
    // Transaction will automatically rollback optimistic changes
    console.error('Delete failed, rolling back:', error)
    throw error
  }
}

#### Inherited from

ts

Omit.onDelete


Omit.onDelete

### onInsert?

ts

optional onInsert: InsertMutationFn<T, TKey, LocalOnlyCollectionUtils, any>;


optional onInsert: InsertMutationFn<T, TKey, LocalOnlyCollectionUtils, any>;

Defined in: packages/db/src/types.ts:527

Optional asynchronous handler function called before an insert operation

#### Param

Object containing transaction and collection information

#### Returns

Promise resolving to any value

#### Examples

ts

// Basic insert handler
onInsert: async ({ transaction, collection }) => {
  const newItem = transaction.mutations[0].modified
  await api.createTodo(newItem)
}


// Basic insert handler
onInsert: async ({ transaction, collection }) => {
  const newItem = transaction.mutations[0].modified
  await api.createTodo(newItem)
}

ts

// Insert handler with multiple items
onInsert: async ({ transaction, collection }) => {
  const items = transaction.mutations.map(m => m.modified)
  await api.createTodos(items)
}


// Insert handler with multiple items
onInsert: async ({ transaction, collection }) => {
  const items = transaction.mutations.map(m => m.modified)
  await api.createTodos(items)
}

ts

// Insert handler with error handling
onInsert: async ({ transaction, collection }) => {
  try {
    const newItem = transaction.mutations[0].modified
    const result = await api.createTodo(newItem)
    return result
  } catch (error) {
    console.error('Insert failed:', error)
    throw error // This will cause the transaction to fail
  }
}


// Insert handler with error handling
onInsert: async ({ transaction, collection }) => {
  try {
    const newItem = transaction.mutations[0].modified
    const result = await api.createTodo(newItem)
    return result
  } catch (error) {
    console.error('Insert failed:', error)
    throw error // This will cause the transaction to fail
  }
}

ts

// Insert handler with metadata
onInsert: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  await api.createTodo(mutation.modified, {
    source: mutation.metadata?.source,
    timestamp: mutation.createdAt
  })
}


// Insert handler with metadata
onInsert: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  await api.createTodo(mutation.modified, {
    source: mutation.metadata?.source,
    timestamp: mutation.createdAt
  })
}

#### Inherited from

ts

Omit.onInsert


Omit.onInsert

### onUpdate?

ts

optional onUpdate: UpdateMutationFn<T, TKey, LocalOnlyCollectionUtils, any>;


optional onUpdate: UpdateMutationFn<T, TKey, LocalOnlyCollectionUtils, any>;

Defined in: packages/db/src/types.ts:571

Optional asynchronous handler function called before an update operation

#### Param

Object containing transaction and collection information

#### Returns

Promise resolving to any value

#### Examples

ts

// Basic update handler
onUpdate: async ({ transaction, collection }) => {
  const updatedItem = transaction.mutations[0].modified
  await api.updateTodo(updatedItem.id, updatedItem)
}


// Basic update handler
onUpdate: async ({ transaction, collection }) => {
  const updatedItem = transaction.mutations[0].modified
  await api.updateTodo(updatedItem.id, updatedItem)
}

ts

// Update handler with partial updates
onUpdate: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  const changes = mutation.changes // Only the changed fields
  await api.updateTodo(mutation.original.id, changes)
}


// Update handler with partial updates
onUpdate: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  const changes = mutation.changes // Only the changed fields
  await api.updateTodo(mutation.original.id, changes)
}

ts

// Update handler with multiple items
onUpdate: async ({ transaction, collection }) => {
  const updates = transaction.mutations.map(m => ({
    id: m.key,
    changes: m.changes
  }))
  await api.updateTodos(updates)
}


// Update handler with multiple items
onUpdate: async ({ transaction, collection }) => {
  const updates = transaction.mutations.map(m => ({
    id: m.key,
    changes: m.changes
  }))
  await api.updateTodos(updates)
}

ts

// Update handler with optimistic rollback
onUpdate: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  try {
    await api.updateTodo(mutation.original.id, mutation.changes)
  } catch (error) {
    // Transaction will automatically rollback optimistic changes
    console.error('Update failed, rolling back:', error)
    throw error
  }
}


// Update handler with optimistic rollback
onUpdate: async ({ transaction, collection }) => {
  const mutation = transaction.mutations[0]
  try {
    await api.updateTodo(mutation.original.id, mutation.changes)
  } catch (error) {
    // Transaction will automatically rollback optimistic changes
    console.error('Update failed, rolling back:', error)
    throw error
  }
}

#### Inherited from

ts

Omit.onUpdate


Omit.onUpdate

### schema?

ts

optional schema: TSchema;


optional schema: TSchema;

Defined in: packages/db/src/types.ts:430

#### Inherited from

ts

Omit.schema


Omit.schema

### syncMode?

ts

optional syncMode: SyncMode;


optional syncMode: SyncMode;

Defined in: packages/db/src/types.ts:485

The mode of sync to use for the collection.

#### Default

eager

#### Description

  • eager: syncs all data immediately on preload
  • on-demand: syncs data in incremental snapshots when the collection is queried The exact implementation of the sync mode is up to the sync implementation.

#### Inherited from

BaseCollectionConfig .syncMode

### utils?

ts

optional utils: LocalOnlyCollectionUtils;


optional utils: LocalOnlyCollectionUtils;

Defined in: packages/db/src/types.ts:624

#### Inherited from

ts

Omit.utils


Omit.utils

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