Class DynamicModule

Creates a dynamic reference to a column that is not know at compile time.

Kysely is built in a way that by default you can't refer to tables or columns that are not actually visible in the current query and context. This is all done by typescript at compile time, which means that you need to know the columns and tables at compile time. This is not always the case of course.

This method is meant to be used in those cases where the column names come from the user input or are not otherwise known at compile time.

WARNING! Unlike values, column names are not escaped by the database engine or Kysely and if you pass in unchecked column names using this method, you create an SQL injection vulnerability. Always always validate the user input before passing it to this method.

There are couple of examples below for some use cases, but you can pass ref to other methods as well. If the types allow you to pass a ref value to some place, it should work.

Examples

Filter by a column not know at compile time:

async function someQuery(filterColumn: string, filterValue: string) {
  const { ref } = db.dynamic

  return await db
    .selectFrom('person')
    .selectAll()
    .where(ref(filterColumn), '=', filterValue)
    .execute()
}

someQuery('first_name', 'Arnold')
someQuery('person.last_name', 'Aniston')
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Order by a column not know at compile time:

async function someQuery(orderBy: string) {
  const { ref } = db.dynamic

  return await db
    .selectFrom('person')
    .select('person.first_name as fn')
    .orderBy(ref(orderBy))
    .execute()
}

someQuery('fn')
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In this example we add selections dynamically:

const { ref } = db.dynamic

// Some column name provided by the user. Value not known at compile time.
const columnFromUserInput = req.query.select;

// A type that lists all possible values `columnFromUserInput` can have.
// You can use `keyof Person` if any column of an interface is allowed.
type PossibleColumns = 'last_name' | 'first_name' | 'birth_date'

const [person] = await db.selectFrom('person')
  .select([
    ref<PossibleColumns>(columnFromUserInput),
    'id'
  ])
  .execute()

// The resulting type contains all `PossibleColumns` as optional fields
// because we cannot know which field was actually selected before
// running the code.
const lastName: string | undefined = person.last_name
const firstName: string | undefined = person.first_name
const birthDate: string | undefined = person.birth_date

// The result type also contains the compile time selection `id`.
person.id
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