Last Updated: 3/10/2026

kysely

• ParseJSONResultsPlugin

Class ParseJSONResultsPlugin

Parses JSON strings in query results into JSON objects.

This plugin can be useful with dialects that don’t automatically parse JSON into objects and arrays but return JSON strings instead.

To apply this plugin globally, pass an instance of it to the plugins option when creating a new Kysely instance:

import  *  as  Sqlite  from  'better-sqlite3' import { Kysely, ParseJSONResultsPlugin, SqliteDialect } from  'kysely' import  type { Database } from  'type-editor'  // imaginary module const  db = new  Kysely< Database>({ dialect:  new  SqliteDialect({ database:  new  Sqlite(':memory:'), }),  plugins: [new  ParseJSONResultsPlugin()],})

To apply this plugin to a single query:

import { ParseJSONResultsPlugin } from  'kysely' import { jsonArrayFrom } from  'kysely/helpers/sqlite' const  result = await  db . selectFrom('person') . select((eb) => [ 'id',  'first_name',  'last_name',  jsonArrayFrom( eb. selectFrom('pet') . whereRef('owner_id', '=', 'person.id') . select(['name', 'species']) ). as('pets') ]) . withPlugin(new  ParseJSONResultsPlugin()) . execute()

Implements

• KyselyPlugin

Index

Constructors

constructor

Properties

opt

Methods

transformQuery transformResult

Constructors

constructor

• new ParseJSONResultsPlugin(
      opt?: ParseJSONResultsPluginOptions,
  ): ParseJSONResultsPlugin

  Parameters

  • opt: ParseJSONResultsPluginOptions = {}

  Returns ParseJSONResultsPlugin

Properties

Readonlyopt

opt: ParseJSONResultsPluginOptions = {}

Methods

transformQuery

• transformQuery(args: PluginTransformQueryArgs): RootOperationNode

  This is called for each query before it is executed. You can modify the query by transforming its OperationNode tree provided in args.node and returning the transformed tree. You’d usually want to use an OperationNodeTransformer for this.

  If you need to pass some query-related data between this method and transformResult you can use a WeakMap with args.queryId as the key:

  import  type { KyselyPlugin,  QueryResult,  RootOperationNode,  UnknownRow} from  'kysely' interface  MyData { // ...} const  data = new  WeakMap< any, MyData>() const  plugin = { transformQuery(args: PluginTransformQueryArgs): RootOperationNode { const  something: MyData = {}  // ...  data. set(args. queryId, something)  // ...  return  args. node },  async  transformResult(args: PluginTransformResultArgs): Promise< QueryResult< UnknownRow>> { // ...  const  something = data. get(args. queryId)  // ...  return  args. result }} satisfies  KyselyPlugin

  You should use a WeakMap instead of a Map or some other strong references because transformQuery is not always matched by a call to transformResult which would leave orphaned items in the map and cause a memory leak.

  Parameters

  • args: PluginTransformQueryArgs

  Returns RootOperationNode

transformResult

• transformResult(
      args: PluginTransformResultArgs,
  ): Promise<QueryResult<UnknownRow>>

  This method is called for each query after it has been executed. The result of the query can be accessed through args.result. You can modify the result and return the modifier result.

  Parameters

  • args: PluginTransformResultArgs

  Returns Promise<QueryResult<UnknownRow>>

Settings

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Constructors

constructor

Properties

opt

Methods

transformQuerytransformResult