ColumnType

Specify different types for select, insert, and update operations on database columns

Type Signature

type ColumnType<
  SelectType,
  InsertType = SelectType,
  UpdateType = SelectType,
> = {
  readonly __select__: SelectType
  readonly __insert__: InsertType
  readonly __update__: UpdateType
}

Overview

ColumnType allows you to specify different types for select, insert, and update operations on a database column. This is particularly useful for:

• Database-generated columns (IDs, timestamps)
• Columns with different input/output formats (dates as strings for insert, Date objects for select)
• Read-only columns that can’t be inserted or updated

Type Parameters

SelectType · type · required

The TypeScript type returned when selecting this column from the database.

InsertType · type · default: "SelectType"

The TypeScript type accepted when inserting this column. Defaults to SelectType if not specified.

UpdateType · type · default: "SelectType"

The TypeScript type accepted when updating this column. Defaults to SelectType if not specified.

Examples

Database-Generated Column

Make a column optional in inserts and updates (useful for auto-incrementing IDs):

interface PersonTable {
  id: ColumnType<number, number | undefined, number>
  name: string
}

The Generated<T> type is a shortcut for this pattern.

Read-Only Column

Prevent insertion and update of a column:

interface PersonTable {
  id: ColumnType<number, never, never>
  name: string
}

The GeneratedAlways<T> type is a shortcut for this pattern.

Different Types Per Operation

Accept strings for insert, but prevent updates and return Date objects for selects:

interface PersonTable {
  id: Generated<number>
  created_at: ColumnType<Date, string, never>
  name: string
}

With this definition:

// Insert accepts string
await db.insertInto('person')
  .values({
    created_at: '2024-01-01',
    name: 'John'
  })
  .execute()

// Select returns Date
const person = await db
  .selectFrom('person')
  .selectAll()
  .executeTakeFirst()
// person.created_at is Date

// Update doesn't allow created_at
await db.updateTable('person')
  .set({
    created_at: '2024-01-02' // Type error!
  })
  .execute()

Related Types

• Generated<T> - Shortcut for database-generated columns
• GeneratedAlways<T> - Shortcut for always-generated columns
• Selectable<T> - Extract select types from a table interface
• Insertable<T> - Extract insert types from a table interface
• Updateable<T> - Extract update types from a table interface

Source

View source on GitHub