fix: implement formula field, list field, and reference field as chilrden of the field class. fix: when converting api response data to appropriate field response make sure json field objects are converted to correct field class based upon type.

src/models/ReferenceField.ts

@@ -0,0 +1,30 @@
+import { Multiplicity } from '../enums/Multiplicity';
+import { Field } from './Field';
+
+export class ReferenceField extends Field {
+  public multiplicity: Multiplicity;
+  public referencedAppId: number;
+
+  constructor(
+    id: number,
+    appId: number,
+    name: string,
+    type: string,
+    status: string,
+    isRequired: boolean,
+    isUnique: boolean,
+    multiplicity: string,
+    referencedAppId: number
+  ) {
+    super(id, appId, name, type, status, isRequired, isUnique);
+
+    if (Multiplicity[multiplicity] === undefined) {
+      throw new Error(
+        `The multiplicity ${multiplicity} is not a valid Multiplicity.`
+      );
+    }
+
+    this.multiplicity = Multiplicity[multiplicity];
+    this.referencedAppId = referencedAppId;
+  }
+}