Support json_agg(column_ref)

src/query-builder/function-module.ts

@@ -24,6 +24,7 @@ import { SelectQueryBuilderExpression } from '../query-builder/select-query-buil
 import { isString } from '../util/object-utils.js'
 import { parseTable } from '../parser/table-parser.js'
 import { Selectable } from '../util/column-type.js'
+import { RawBuilder } from '../raw-builder/raw-builder.js'
 
 /**
  * Helpers for type safe SQL function calls.
@@ -657,6 +658,8 @@ export interface FunctionModule<DB, TB extends keyof DB> {
    *
    * This function is only available on PostgreSQL.
    *
+   * You can use it either on a table:
+   *
    * ```ts
    * await db.selectFrom('person')
    *   .innerJoin('pet', 'pet.owner_id', 'person.id')
@@ -673,6 +676,44 @@ export interface FunctionModule<DB, TB extends keyof DB> {
    * inner join "pet" on "pet"."owner_id" = "person"."id"
    * group by "person"."first_name"
    * ```
+   *
+   * ... or on a column:
+   *
+   * ```ts
+   * await db.selectFrom('person')
+   *   .innerJoin('pet', 'pet.owner_id', 'person.id')
+   *   .select((eb) => ['first_name', eb.fn.jsonAgg('pet.names').as('pet_names')])
+   *   .groupBy('person.first_name')
+   *   .execute()
+   *
+   * await db.selectFrom('person')
+   *   .select((eb) => [
+   *     'first_name',
+   *     eb
+   *       .selectFrom('pet')
+   *       .select((eb) => [eb.fn.jsonAgg("pet.owner_id")])
+   *       .whereRef('pet.owner_id', '=', 'person.id')
+   *       .as('petnames'),
+   *   ])
+   *   .execute()
+   * ```
+   *
+   * The generated SQL (PostgreSQL):
+   *
+   * ```sql
+   * select "first_name", json_agg("pet"."names") AS "pet_names"
+   * from "person"
+   * inner join "pet" ON "pet"."owner_id" = "person"."id"
+   * group by "person"."first_name"
+   *
+   * select "first_name",
+   *   (
+   *     select json_agg("pet"."owner_id")
+   *     from "pet"
+   *     where "pet"."owner_id" = "person"."id"
+   *   ) as "petnames"
+   * from "person"
+   * ```
    */
   jsonAgg<T extends (TB & string) | Expression<unknown>>(
     table: T,
@@ -685,6 +726,9 @@ export interface FunctionModule<DB, TB extends keyof DB> {
         ? O[]
         : never
   >
+  jsonAgg<RE extends StringReference<DB, TB>>(
+    column: RE,
+  ): RawBuilder<ExtractTypeFromStringReference<DB, TB, RE>[] | null>
 
   /**
    * Creates a to_json function call.

test/typings/test-d/postgres-json.test-d.ts

@@ -169,6 +169,39 @@ async function testPostgresJsonAgg(db: Kysely<Database>) {
       status: string | null
     }[]
   }>(r4)
+
+  const r5 = await db
+    .selectFrom('person')
+    .innerJoin('pet', 'pet.owner_id', 'person.id')
+    .select((eb) => ['first_name', eb.fn.jsonAgg('owner_id').as('pet_names')])
+    .groupBy('person.first_name')
+    .execute()
+
+  expectType<
+    {
+      first_name: string
+      pet_names: number[] | null
+    }[]
+  >(r5)
+
+  const r6 = await db
+    .selectFrom('person')
+    .select((eb) => [
+      'first_name',
+      eb
+        .selectFrom('pet')
+        .select((eb) => [eb.fn.jsonAgg('pet.owner_id').as('pet_names')])
+        .whereRef('pet.owner_id', '=', 'person.id')
+        .as('pet_names'),
+    ])
+    .execute()
+
+  expectType<
+    {
+      first_name: string
+      pet_names: number[] | null
+    }[]
+  >(r6)
 }
 
 async function testPostgresToJson(db: Kysely<Database>) {