Add registering of client-side relationship properties (#5936)

app/models/Comment.ts

@@ -34,6 +34,12 @@ class Comment extends Model {
   @observable
   parentCommentId: string;
 
+  /**
+   * The comment that this comment is a reply to.
+   */
+  @Relation(() => Comment, { onDelete: "cascade" })
+  parentComment?: Comment;
+
   /**
    * The document to which this comment belongs.
    */

app/models/Notification.ts

@@ -47,7 +47,7 @@ class Notification extends Model {
   /**
    * The document that the notification is associated with.
    */
-  @Relation(() => Document)
+  @Relation(() => Document, { onDelete: "cascade" })
   document?: Document;
 
   /**
@@ -58,7 +58,7 @@ class Notification extends Model {
   /**
    * The comment that the notification is associated with.
    */
-  @Relation(() => Comment)
+  @Relation(() => Comment, { onDelete: "cascade" })
   comment?: Comment;
 
   /**

app/models/base/Model.ts

@@ -95,12 +95,12 @@ export default abstract class Model {
    */
   toAPI = (): Record<string, any> => {
     const fields = getFieldsForModel(this);
-    return pick(this, fields) || [];
+    return pick(this, fields);
   };
 
   /**
    * Returns a plain object representation of all the properties on the model
-   * overrides the inbuilt toJSON method to avoid attempting to serialize store
+   * overrides the native toJSON method to avoid attempting to serialize store
    *
    * @returns {Record<string, any>}
    */

app/models/decorators/Field.ts

@@ -1,9 +1,9 @@
 import type Model from "../base/Model";
 
-const fields = new Map();
+const fields = new Map<string, string[]>();
 
 export const getFieldsForModel = (target: Model) =>
-  fields.get(target.constructor.name);
+  fields.get(target.constructor.name) ?? [];
 
 /**
  * A decorator that records this key as a serializable field on the model.
@@ -14,7 +14,10 @@ export const getFieldsForModel = (target: Model) =>
  */
 const Field = <T>(target: any, propertyKey: keyof T) => {
   const className = target.constructor.name;
-  fields.set(className, [...(fields.get(className) || []), propertyKey]);
+  fields.set(className, [
+    ...(fields.get(className) || []),
+    propertyKey as string,
+  ]);
 };
 
 export default Field;

app/models/decorators/Relation.ts

@@ -4,6 +4,47 @@ import type Model from "../base/Model";
 type RelationOptions = {
   /** Whether this relation is required */
   required?: boolean;
+  /** Behavior of relationship on deletion */
+  onDelete: "cascade" | "null" | "ignore";
+};
+
+type RelationProperties = {
+  /** The name of the property on the model that stores the ID of the relation */
+  idKey: string;
+  /** A function that returns the class of the relation */
+  relationClassResolver: () => typeof Model;
+  /** Options for the relation */
+  options: RelationOptions;
+};
+
+type InverseRelationProperties = RelationProperties & {
+  /** The name of the model class that owns this relation */
+  modelName: string;
+};
+
+const relations = new Map<string, Map<string, RelationProperties>>(new Map());
+
+/**
+ * Returns the inverse relation properties for the given model class.
+ *
+ * @param targetClass The model class to get inverse relations for.
+ * @returns A map of inverse relation properties keyed by the property name.
+ */
+export const getInverseRelationsForModelClass = (targetClass: typeof Model) => {
+  const inverseRelations = new Map<string, InverseRelationProperties>();
+
+  relations.forEach((relation, modelName) => {
+    relation.forEach((properties, propertyName) => {
+      if (properties.relationClassResolver().name === targetClass.name) {
+        inverseRelations.set(propertyName, {
+          ...properties,
+          modelName,
+        });
+      }
+    });
+  });
+
+  return inverseRelations;
 };
 
 /**
@@ -20,8 +61,19 @@ export default function Relation<T extends typeof Model>(
 ) {
   return function (target: any, propertyKey: string) {
     const idKey = `${String(propertyKey)}Id`;
-    const relationClass = classResolver();
-    const relationClassName = relationClass.name;
+
+    // If the relation has options provided then register them in a map for later lookup. We can use
+    // this to determine how to update relations when a model is deleted.
+    if (options) {
+      const configForClass =
+        relations.get(target.constructor.name) || new Map();
+      configForClass.set(propertyKey, {
+        options,
+        relationClassResolver: classResolver,
+        idKey,
+      });
+      relations.set(target.constructor.name, configForClass);
+    }
 
     Object.defineProperty(target, propertyKey, {
       get() {
@@ -31,6 +83,7 @@ export default function Relation<T extends typeof Model>(
           return undefined;
         }
 
+        const relationClassName = classResolver().name;
         const store =
           this.store.rootStore[`${relationClassName.toLowerCase()}s`];
         invariant(store, `Store for ${relationClassName} not found`);
@@ -41,6 +94,7 @@ export default function Relation<T extends typeof Model>(
         this[idKey] = newValue ? newValue.id : undefined;
 
         if (newValue) {
+          const relationClassName = classResolver().name;
           const store =
             this.store.rootStore[`${relationClassName.toLowerCase()}s`];
           invariant(store, `Store for ${relationClassName} not found`);