@tanstack/db/src/query/builder/functions.ts

A reactive client store for building super fast apps on sync

import { Aggregate, Func } from '../ir'
import { isRefProxy, toExpression } from './ref-proxy.js'
import type { BasicExpression } from '../ir'
import type { RefProxy } from './ref-proxy.js'
import type { SingleResult } from '../../types.js'
import type {
  Context,
  GetRawResult,
  RefLeaf,
  StringifiableScalar,
} from './types.js'
import type { QueryBuilder } from './index.js'

type StringRef =
  | RefLeaf<string>
  | RefLeaf<string | null>
  | RefLeaf<string | undefined>
type StringRefProxy =
  | RefProxy<string>
  | RefProxy<string | null>
  | RefProxy<string | undefined>
type StringBasicExpression =
  | BasicExpression<string>
  | BasicExpression<string | null>
  | BasicExpression<string | undefined>
type StringLike =
  | StringRef
  | StringRefProxy
  | StringBasicExpression
  | string
  | null
  | undefined

type ComparisonOperand<T> =
  | RefProxy<T>
  | RefLeaf<T>
  | T
  | BasicExpression<T>
  | undefined
  | null
type ComparisonOperandPrimitive<T extends string | number | boolean> =
  | T
  | BasicExpression<T>
  | undefined
  | null

// Helper type for values that can be lowered to expressions.
type ExpressionLike =
  | Aggregate
  | BasicExpression
  | RefProxy<any>
  | RefLeaf<any>
  | string
  | number
  | boolean
  | bigint
  | Date
  | null
  | undefined
  | Array<unknown>

type CaseWhenValue =
  | ExpressionLike
  | QueryBuilder<any>
  | ToArrayWrapper<any>
  | ConcatToArrayWrapper<any>
  | Record<string, any>

type ExtractCaseWhenValue<T> =
  T extends CaseWhenWrapper<infer TResult> ? TResult : T

type CaseWhenResult<
  TValues extends Array<CaseWhenValue>,
  THasDefault extends boolean,
> = TValues[number] extends ExpressionLike
  ? BasicExpression<
      ExtractType<TValues[number]> | (THasDefault extends true ? never : null)
    >
  : CaseWhenWrapper<
      | ExtractCaseWhenValue<TValues[number]>
      | (THasDefault extends true ? never : undefined)
    >

// Helper type to extract the underlying type from various expression types
type ExtractType<T> =
  T extends RefProxy<infer U>
    ? U
    : T extends RefLeaf<infer U>
      ? U
      : T extends BasicExpression<infer U>
        ? U
        : T

// Helper type to determine aggregate return type based on input nullability
type AggregateReturnType<T> =
  ExtractType<T> extends infer U
    ? U extends number | undefined | null | Date | bigint | string
      ? Aggregate<U>
      : Aggregate<number | undefined | null | Date | bigint | string>
    : Aggregate<number | undefined | null | Date | bigint | string>

// Helper type to determine string function return type based on input nullability
type StringFunctionReturnType<T> =
  ExtractType<T> extends infer U
    ? U extends string | undefined | null
      ? BasicExpression<U>
      : BasicExpression<string | undefined | null>
    : BasicExpression<string | undefined | null>

// Helper type to determine numeric function return type based on input nullability
// This handles string, array, and number inputs for functions like length()
type NumericFunctionReturnType<T> =
  ExtractType<T> extends infer U
    ? U extends string | Array<any> | undefined | null | number
      ? BasicExpression<MapToNumber<U>>
      : BasicExpression<number | undefined | null>
    : BasicExpression<number | undefined | null>

// Transform string/array types to number while preserving nullability
type MapToNumber<T> = T extends string | Array<any>
  ? number
  : T extends undefined
    ? undefined
    : T extends null
      ? null
      : T

// Helper type for binary numeric operations (combines nullability of both operands)
type BinaryNumericReturnType<T1, T2> =
  ExtractType<T1> extends infer U1
    ? ExtractType<T2> extends infer U2
      ? U1 extends number
        ? U2 extends number
          ? BasicExpression<number>
          : U2 extends number | undefined
            ? BasicExpression<number | undefined>
            : U2 extends number | null
              ? BasicExpression<number | null>
              : BasicExpression<number | undefined | null>
        : U1 extends number | undefined
          ? U2 extends number
            ? BasicExpression<number | undefined>
            : U2 extends number | undefined
              ? BasicExpression<number | undefined>
              : BasicExpression<number | undefined | null>
          : U1 extends number | null
            ? U2 extends number
              ? BasicExpression<number | null>
              : BasicExpression<number | undefined | null>
            : BasicExpression<number | undefined | null>
      : BasicExpression<number | undefined | null>
    : BasicExpression<number | undefined | null>

// Operators

export function eq<T>(
  left: ComparisonOperand<T>,
  right: ComparisonOperand<T>,
): BasicExpression<boolean>
export function eq<T extends string | number | boolean>(
  left: ComparisonOperandPrimitive<T>,
  right: ComparisonOperandPrimitive<T>,
): BasicExpression<boolean>
export function eq<T>(left: Aggregate<T>, right: any): BasicExpression<boolean>
export function eq(left: any, right: any): BasicExpression<boolean> {
  return new Func(`eq`, [toExpression(left), toExpression(right)])
}

export function gt<T>(
  left: ComparisonOperand<T>,
  right: ComparisonOperand<T>,
): BasicExpression<boolean>
export function gt<T extends string | number>(
  left: ComparisonOperandPrimitive<T>,
  right: ComparisonOperandPrimitive<T>,
): BasicExpression<boolean>
export function gt<T>(left: Aggregate<T>, right: any): BasicExpression<boolean>
export function gt(left: any, right: any): BasicExpression<boolean> {
  return new Func(`gt`, [toExpression(left), toExpression(right)])
}

export function gte<T>(
  left: ComparisonOperand<T>,
  right: ComparisonOperand<T>,
): BasicExpression<boolean>
export function gte<T extends string | number>(
  left: ComparisonOperandPrimitive<T>,
  right: ComparisonOperandPrimitive<T>,
): BasicExpression<boolean>
export function gte<T>(left: Aggregate<T>, right: any): BasicExpression<boolean>
export function gte(left: any, right: any): BasicExpression<boolean> {
  return new Func(`gte`, [toExpression(left), toExpression(right)])
}

export function lt<T>(
  left: ComparisonOperand<T>,
  right: ComparisonOperand<T>,
): BasicExpression<boolean>
export function lt<T extends string | number>(
  left: ComparisonOperandPrimitive<T>,
  right: ComparisonOperandPrimitive<T>,
): BasicExpression<boolean>
export function lt<T>(left: Aggregate<T>, right: any): BasicExpression<boolean>
export function lt(left: any, right: any): BasicExpression<boolean> {
  return new Func(`lt`, [toExpression(left), toExpression(right)])
}

export function lte<T>(
  left: ComparisonOperand<T>,
  right: ComparisonOperand<T>,
): BasicExpression<boolean>
export function lte<T extends string | number>(
  left: ComparisonOperandPrimitive<T>,
  right: ComparisonOperandPrimitive<T>,
): BasicExpression<boolean>
export function lte<T>(left: Aggregate<T>, right: any): BasicExpression<boolean>
export function lte(left: any, right: any): BasicExpression<boolean> {
  return new Func(`lte`, [toExpression(left), toExpression(right)])
}

// Overloads for and() - support 2 or more arguments
export function and(
  left: ExpressionLike,
  right: ExpressionLike,
): BasicExpression<boolean>
export function and(
  left: ExpressionLike,
  right: ExpressionLike,
  ...rest: Array<ExpressionLike>
): BasicExpression<boolean>
export function and(
  left: ExpressionLike,
  right: ExpressionLike,
  ...rest: Array<ExpressionLike>
): BasicExpression<boolean> {
  const allArgs = [left, right, ...rest]
  return new Func(
    `and`,
    allArgs.map((arg) => toExpression(arg)),
  )
}

// Overloads for or() - support 2 or more arguments
export function or(
  left: ExpressionLike,
  right: ExpressionLike,
): BasicExpression<boolean>
export function or(
  left: ExpressionLike,
  right: ExpressionLike,
  ...rest: Array<ExpressionLike>
): BasicExpression<boolean>
export function or(
  left: ExpressionLike,
  right: ExpressionLike,
  ...rest: Array<ExpressionLike>
): BasicExpression<boolean> {
  const allArgs = [left, right, ...rest]
  return new Func(
    `or`,
    allArgs.map((arg) => toExpression(arg)),
  )
}

export function not(value: ExpressionLike): BasicExpression<boolean> {
  return new Func(`not`, [toExpression(value)])
}

// Null/undefined checking functions
export function isUndefined(value: ExpressionLike): BasicExpression<boolean> {
  return new Func(`isUndefined`, [toExpression(value)])
}

export function isNull(value: ExpressionLike): BasicExpression<boolean> {
  return new Func(`isNull`, [toExpression(value)])
}

export function inArray(
  value: ExpressionLike,
  array: ExpressionLike,
): BasicExpression<boolean> {
  return new Func(`in`, [toExpression(value), toExpression(array)])
}

export function like(
  left: StringLike,
  right: StringLike,
): BasicExpression<boolean>
export function like(left: any, right: any): BasicExpression<boolean> {
  return new Func(`like`, [toExpression(left), toExpression(right)])
}

export function ilike(
  left: StringLike,
  right: StringLike,
): BasicExpression<boolean> {
  return new Func(`ilike`, [toExpression(left), toExpression(right)])
}

// Functions

export function upper<T extends ExpressionLike>(
  arg: T,
): StringFunctionReturnType<T> {
  return new Func(`upper`, [toExpression(arg)]) as StringFunctionReturnType<T>
}

export function lower<T extends ExpressionLike>(
  arg: T,
): StringFunctionReturnType<T> {
  return new Func(`lower`, [toExpression(arg)]) as StringFunctionReturnType<T>
}

export function length<T extends ExpressionLike>(
  arg: T,
): NumericFunctionReturnType<T> {
  return new Func(`length`, [toExpression(arg)]) as NumericFunctionReturnType<T>
}

export function concat<T extends StringifiableScalar>(
  arg: ToArrayWrapper<T>,
): ConcatToArrayWrapper<T>
export function concat(...args: Array<ExpressionLike>): BasicExpression<string>
export function concat(
  ...args: Array<ExpressionLike | ToArrayWrapper<any>>
): BasicExpression<string> | ConcatToArrayWrapper<any> {
  const toArrayArg = args.find(
    (arg): arg is ToArrayWrapper<any> => arg instanceof ToArrayWrapper,
  )

  if (toArrayArg) {
    if (args.length !== 1) {
      throw new Error(
        `concat(toArray(...)) currently supports only a single toArray(...) argument`,
      )
    }
    return new ConcatToArrayWrapper(toArrayArg.query)
  }

  return new Func(
    `concat`,
    args.map((arg) => toExpression(arg)),
  )
}

// Helper type for coalesce: extracts non-nullish value types from all args
type CoalesceArgTypes<T extends Array<ExpressionLike>> = {
  [K in keyof T]: NonNullable<ExtractType<T[K]>>
}[number]

// Whether any arg in the tuple is statically guaranteed non-null (i.e., does not include null | undefined)
type HasGuaranteedNonNull<T extends Array<ExpressionLike>> = {
  [K in keyof T]: null extends ExtractType<T[K]>
    ? false
    : undefined extends ExtractType<T[K]>
      ? false
      : true
}[number] extends false
  ? false
  : true

// coalesce() return type: union of all non-null arg types; null included unless a guaranteed non-null arg exists
type CoalesceReturnType<T extends Array<ExpressionLike>> =
  HasGuaranteedNonNull<T> extends true
    ? BasicExpression<CoalesceArgTypes<T>>
    : BasicExpression<CoalesceArgTypes<T> | null>

export function coalesce<T extends [ExpressionLike, ...Array<ExpressionLike>]>(
  ...args: T
): CoalesceReturnType<T> {
  return new Func(
    `coalesce`,
    args.map((arg) => toExpression(arg)),
  ) as CoalesceReturnType<T>
}

/**
 * Returns the value for the first matching condition, similar to SQL
 * `CASE WHEN`.
 *
 * Arguments are evaluated as condition/value pairs followed by an optional
 * default value. Scalar branch values return a query expression and can be used
 * in expression contexts like `select`, `where`, `orderBy`, `groupBy`,
 * `having`, and equality join operands. If no scalar branch matches and no
 * default is provided, the result is `null`.
 *
 * When a branch value is a projection object, `caseWhen` becomes a select-only
 * projection value. Projection branches can include nested fields, ref spreads,
 * and includes. If no projection branch matches and no default is provided, the
 * result is `undefined`.
 *
 * @example
 * ```ts
 * caseWhen(gt(user.age, 18), `adult`, `minor`)
 * ```
 *
 * @example
 * ```ts
 * caseWhen(
 *   gt(user.age, 65),
 *   `senior`,
 *   gt(user.age, 18),
 *   `adult`,
 *   `minor`,
 * )
 * ```
 *
 * @example
 * ```ts
 * caseWhen(gt(user.age, 18), {
 *   ...user,
 *   posts: q
 *     .from({ post: postsCollection })
 *     .where(({ post }) => eq(post.userId, user.id)),
 * })
 * ```
 */
export function caseWhen<C1 extends ExpressionLike, V1 extends CaseWhenValue>(
  condition1: C1,
  value1: V1,
): CaseWhenResult<[V1], false>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  D extends CaseWhenValue,
>(condition1: C1, value1: V1, defaultValue: D): CaseWhenResult<[V1, D], true>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
): CaseWhenResult<[V1, V2], false>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  D extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  defaultValue: D,
): CaseWhenResult<[V1, V2, D], true>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  C3 extends ExpressionLike,
  V3 extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  condition3: C3,
  value3: V3,
): CaseWhenResult<[V1, V2, V3], false>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  C3 extends ExpressionLike,
  V3 extends CaseWhenValue,
  D extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  condition3: C3,
  value3: V3,
  defaultValue: D,
): CaseWhenResult<[V1, V2, V3, D], true>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  C3 extends ExpressionLike,
  V3 extends CaseWhenValue,
  C4 extends ExpressionLike,
  V4 extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  condition3: C3,
  value3: V3,
  condition4: C4,
  value4: V4,
): CaseWhenResult<[V1, V2, V3, V4], false>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  C3 extends ExpressionLike,
  V3 extends CaseWhenValue,
  C4 extends ExpressionLike,
  V4 extends CaseWhenValue,
  D extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  condition3: C3,
  value3: V3,
  condition4: C4,
  value4: V4,
  defaultValue: D,
): CaseWhenResult<[V1, V2, V3, V4, D], true>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  C3 extends ExpressionLike,
  V3 extends CaseWhenValue,
  C4 extends ExpressionLike,
  V4 extends CaseWhenValue,
  C5 extends ExpressionLike,
  V5 extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  condition3: C3,
  value3: V3,
  condition4: C4,
  value4: V4,
  condition5: C5,
  value5: V5,
): CaseWhenResult<[V1, V2, V3, V4, V5], false>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  C3 extends ExpressionLike,
  V3 extends CaseWhenValue,
  C4 extends ExpressionLike,
  V4 extends CaseWhenValue,
  C5 extends ExpressionLike,
  V5 extends CaseWhenValue,
  D extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  condition3: C3,
  value3: V3,
  condition4: C4,
  value4: V4,
  condition5: C5,
  value5: V5,
  defaultValue: D,
): CaseWhenResult<[V1, V2, V3, V4, V5, D], true>
export function caseWhen<
  C1 extends ExpressionLike,
  V1 extends CaseWhenValue,
  C2 extends ExpressionLike,
  V2 extends CaseWhenValue,
  C3 extends ExpressionLike,
  V3 extends CaseWhenValue,
  C4 extends ExpressionLike,
  V4 extends CaseWhenValue,
  C5 extends ExpressionLike,
  V5 extends CaseWhenValue,
>(
  condition1: C1,
  value1: V1,
  condition2: C2,
  value2: V2,
  condition3: C3,
  value3: V3,
  condition4: C4,
  value4: V4,
  condition5: C5,
  value5: V5,
  condition6: ExpressionLike,
  value6: CaseWhenValue,
  ...rest: Array<CaseWhenValue>
): any
export function caseWhen(...args: Array<CaseWhenValue>): any {
  if (args.length < 2) {
    throw new Error(`caseWhen() requires at least two arguments`)
  }

  const pairCount = Math.floor(args.length / 2)
  for (let i = 0; i < pairCount; i++) {
    const condition = args[i * 2]
    if (!isConditionValue(condition)) {
      throw new Error(`caseWhen() conditions must be expression-like values`)
    }
  }

  if (caseWhenHasOnlyExpressionValues(args)) {
    return new Func(
      `caseWhen`,
      args.map((arg) => toExpression(arg)),
    )
  }

  return new CaseWhenWrapper(args)
}

export function add<T1 extends ExpressionLike, T2 extends ExpressionLike>(
  left: T1,
  right: T2,
): BinaryNumericReturnType<T1, T2> {
  return new Func(`add`, [
    toExpression(left),
    toExpression(right),
  ]) as BinaryNumericReturnType<T1, T2>
}

// Aggregates

export function count(arg: ExpressionLike): Aggregate<number> {
  return new Aggregate(`count`, [toExpression(arg)])
}

export function avg<T extends ExpressionLike>(arg: T): AggregateReturnType<T> {
  return new Aggregate(`avg`, [toExpression(arg)]) as AggregateReturnType<T>
}

export function sum<T extends ExpressionLike>(arg: T): AggregateReturnType<T> {
  return new Aggregate(`sum`, [toExpression(arg)]) as AggregateReturnType<T>
}

export function min<T extends ExpressionLike>(arg: T): AggregateReturnType<T> {
  return new Aggregate(`min`, [toExpression(arg)]) as AggregateReturnType<T>
}

export function max<T extends ExpressionLike>(arg: T): AggregateReturnType<T> {
  return new Aggregate(`max`, [toExpression(arg)]) as AggregateReturnType<T>
}

/**
 * List of comparison function names that can be used with indexes
 */
export const comparisonFunctions = [
  `eq`,
  `gt`,
  `gte`,
  `lt`,
  `lte`,
  `in`,
  `like`,
  `ilike`,
] as const

/**
 * All supported operator names in TanStack DB expressions
 */
export const operators = [
  // Comparison operators
  `eq`,
  `gt`,
  `gte`,
  `lt`,
  `lte`,
  `in`,
  `like`,
  `ilike`,
  // Logical operators
  `and`,
  `or`,
  `not`,
  // Null checking
  `isNull`,
  `isUndefined`,
  // String functions
  `upper`,
  `lower`,
  `length`,
  `concat`,
  // Numeric functions
  `add`,
  // Utility functions
  `coalesce`,
  `caseWhen`,
  // Aggregate functions
  `count`,
  `avg`,
  `sum`,
  `min`,
  `max`,
] as const

export type OperatorName = (typeof operators)[number]

export class ToArrayWrapper<_T = unknown> {
  readonly __brand = `ToArrayWrapper` as const
  declare readonly _type: `toArray`
  declare readonly _result: _T
  constructor(public readonly query: QueryBuilder<any>) {}
}

export class ConcatToArrayWrapper<_T = unknown> {
  readonly __brand = `ConcatToArrayWrapper` as const
  declare readonly _type: `concatToArray`
  declare readonly _result: _T
  constructor(public readonly query: QueryBuilder<any>) {}
}

export class CaseWhenWrapper<_T = any> {
  readonly __brand = `CaseWhenWrapper` as const
  declare readonly _type: `caseWhen`
  readonly _result?: _T
  constructor(public readonly args: Array<CaseWhenValue>) {}
}

export class MaterializeWrapper<
  _T = unknown,
  _IsSingle extends boolean = boolean,
> {
  readonly __brand = `MaterializeWrapper` as const
  declare readonly _type: `materialize`
  declare readonly _result: _T
  declare readonly _isSingle: _IsSingle
  constructor(public readonly query: QueryBuilder<any>) {}
}

export function toArray<TContext extends Context>(
  query: QueryBuilder<TContext>,
): ToArrayWrapper<GetRawResult<TContext>> {
  return new ToArrayWrapper(query)
}

function caseWhenHasOnlyExpressionValues(args: Array<CaseWhenValue>): boolean {
  const valueIndexes = getCaseWhenValueIndexes(args.length)
  return valueIndexes.every((index) => isExpressionValue(args[index]))
}

function getCaseWhenValueIndexes(argCount: number): Array<number> {
  const valueIndexes: Array<number> = []
  const hasDefaultValue = argCount % 2 === 1
  const pairCount = Math.floor(argCount / 2)

  for (let i = 0; i < pairCount; i++) {
    valueIndexes.push(i * 2 + 1)
  }

  if (hasDefaultValue) {
    valueIndexes.push(argCount - 1)
  }

  return valueIndexes
}

function isExpressionValue(value: CaseWhenValue | undefined): boolean {
  if (isRefProxy(value)) return true
  if (value instanceof Aggregate || value instanceof Func) return true
  if (value == null) return true
  if (
    typeof value === `string` ||
    typeof value === `number` ||
    typeof value === `boolean` ||
    typeof value === `bigint`
  ) {
    return true
  }
  if (value instanceof Date || Array.isArray(value)) return true
  if (typeof value === `object`) {
    const candidate = value as {
      type?: unknown
      args?: unknown
      name?: unknown
      path?: unknown
      value?: unknown
    }

    if (
      (candidate.type === `agg` || candidate.type === `func`) &&
      typeof candidate.name === `string` &&
      Array.isArray(candidate.args)
    ) {
      return true
    }
    if (candidate.type === `ref` && Array.isArray(candidate.path)) return true
    if (candidate.type === `val` && `value` in candidate) return true
  }
  return false
}

function isConditionValue(value: CaseWhenValue | undefined): boolean {
  return isExpressionValue(value) && !Array.isArray(value)
}

/**
 * Materialize an includes subquery into a plain value on the parent row.
 *
 * - For multi-row subqueries, the parent receives an `Array<T>` snapshot
 *   (equivalent to `toArray()`).
 * - For `findOne()` subqueries, the parent receives a single `T | undefined`
 *   value — `undefined` when no child matches.
 *
 * The snapshot updates reactively: parent rows re-emit when the underlying
 * children change.
 *
 * @example
 * ```ts
 * // Multi-row: produces Array<Issue> on each project
 * select(({ p }) => ({
 *   ...p,
 *   issues: materialize(
 *     q.from({ i: issues }).where(({ i }) => eq(i.projectId, p.id)),
 *   ),
 * }))
 *
 * // Singleton: produces Author | undefined on each post
 * select(({ p }) => ({
 *   ...p,
 *   author: materialize(
 *     q.from({ a: authors }).where(({ a }) => eq(a.id, p.authorId)).findOne(),
 *   ),
 * }))
 * ```
 */
export function materialize<TContext extends Context>(
  query: QueryBuilder<TContext>,
): MaterializeWrapper<
  GetRawResult<TContext>,
  TContext extends SingleResult ? true : false
> {
  return new MaterializeWrapper(query)
}