Initial

module/data/fields/collectionField.mjs

@@ -0,0 +1,25 @@
+export default class CollectionField extends foundry.data.fields.TypedObjectField {
+    constructor(model, options = { collectionClass: foundry.utils.Collection }, context = {}) {
+        super(new foundry.data.fields.EmbeddedDataField(model), options, context);
+        this.#elementClass = model;
+        this.#collectionClass = options.collectionClass;
+    }
+
+    /**
+     * The collection class
+     */
+    #collectionClass;
+
+    /**
+     * The collection element class.
+     */
+    #elementClass;
+
+    initialize(value, model, _options = {}) {
+        console.log(model);
+        const collection = new this.#collectionClass(
+            Object.entries(value).map(([key, value]) => [key, new this.#elementClass(value)])
+        );
+        return collection;
+    }
+}