3 files changed, 21 insertions, 12 deletions

diff --git a/src/new_fields/Doc.ts b/src/new_fields/Doc.ts
index 8cbd8cf38..10e8fe7ec 100644
--- a/src/new_fields/Doc.ts
+++ b/src/new_fields/Doc.ts
@@ -32,9 +32,8 @@ export class ObjectField {
 
 export type Field = number | string | boolean | ObjectField | RefField;
 export type Opt<T> = T | undefined;
-export type FieldWaiting = null;
-export const FieldWaiting: FieldWaiting = null;
-export type FieldValue<T extends Field = Field> = Opt<T> | FieldWaiting;
+export type FieldWaiting<T extends Field = Field> = Promise<T | undefined>;
+export type FieldValue<T extends Field = Field> = Opt<T> | FieldWaiting<T>;
 
 export const Self = Symbol("Self");
 
@@ -58,7 +57,7 @@ export class Doc extends RefField {
 
     @serializable(alias("fields", map(autoObject())))
     @observable
-    private __fields: { [key: string]: Field | null | undefined } = {};
+    private __fields: { [key: string]: Field | FieldWaiting | undefined } = {};
 
     private [Update] = (diff: any) => {
         DocServer.UpdateField(this[Id], diff);
@@ -78,7 +77,7 @@ export namespace Doc {
             return Cast(field, ctor);
         });
     }
-    export function Get(doc: Doc, key: string, ignoreProto: boolean = false): Field | null | undefined {
+    export function Get(doc: Doc, key: string, ignoreProto: boolean = false): FieldValue {
         const self = doc[Self];
         return getField(self, key, ignoreProto);
     }
diff --git a/src/new_fields/Proxy.ts b/src/new_fields/Proxy.ts
index 6a78388c1..2aa78731e 100644
--- a/src/new_fields/Proxy.ts
+++ b/src/new_fields/Proxy.ts
@@ -50,6 +50,6 @@ export class ProxyField<T extends RefField> extends ObjectField {
             }));
         }
         callback && this.promise.then(callback);
-        return null;
+        return this.promise;
     }
 }
diff --git a/src/new_fields/Types.ts b/src/new_fields/Types.ts
index 0fbd8984c..0392dc2fb 100644
--- a/src/new_fields/Types.ts
+++ b/src/new_fields/Types.ts
@@ -1,4 +1,4 @@
-import { Field, Opt } from "./Doc";
+import { Field, Opt, FieldWaiting, FieldValue } from "./Doc";
 import { List } from "./List";
 
 export type ToType<T> =
@@ -6,7 +6,7 @@ export type ToType<T> =
     T extends "number" ? number :
     T extends "boolean" ? boolean :
     T extends ListSpec<infer U> ? List<U> :
-    T extends { new(...args: any[]): infer R } ? R : never;
+    T extends { new(...args: any[]): infer R } ? (R | Promise<R>) : never;
 
 export type ToConstructor<T> =
     T extends string ? "string" :
@@ -35,10 +35,13 @@ export interface Interface {
 
 export type FieldCtor<T extends Field> = T extends List<infer R> ? ListSpec<R> : ToConstructor<T>;
 
-export function Cast<T extends FieldCtor<Field>>(field: Field | null | undefined, ctor: T): ToType<T> | null | undefined;
-export function Cast<T extends FieldCtor<Field>>(field: Field | null | undefined, ctor: T, defaultVal: ToType<T>): ToType<T>;
-export function Cast<T extends FieldCtor<Field>>(field: Field | null | undefined, ctor: T, defaultVal?: ToType<T>): ToType<T> | null | undefined {
-    if (field !== undefined && field !== null) {
+export function Cast<T extends FieldCtor<Field>>(field: Field | FieldWaiting | undefined, ctor: T): FieldValue<ToType<T>>;
+export function Cast<T extends FieldCtor<Field>>(field: Field | FieldWaiting | undefined, ctor: T, defaultVal: ToType<T>): ToType<T>;
+export function Cast<T extends FieldCtor<Field>>(field: Field | FieldWaiting | undefined, ctor: T, defaultVal?: ToType<T>): FieldValue<ToType<T>> | undefined {
+    if (field instanceof Promise) {
+        return defaultVal === undefined ? field.then(f => Cast(f, ctor) as any) : defaultVal;
+    }
+    if (field !== undefined && !(field instanceof Promise)) {
         if (typeof ctor === "string") {
             if (typeof field === ctor) {
                 return field as ToType<T>;
@@ -59,3 +62,10 @@ export function FieldValue<T extends Field>(field: Opt<T> | Promise<Opt<T>>): Op
 export function FieldValue<T extends Field>(field: Opt<T> | Promise<Opt<T>>, defaultValue?: T): Opt<T> {
     return field instanceof Promise ? defaultValue : field;
 }
+
+export interface PromiseLike<T> {
+    then(callback: (field: Opt<T> | PromiseLike<T>) => void): void;
+}
+export function PromiseValue<T extends Field>(field: FieldValue<T>): PromiseLike<Opt<T>> {
+    return field instanceof Promise ? field : { then(cb: ((field: Opt<T>) => void)) { return cb(field); } };
+}
\ No newline at end of file