feat: add transformPayloadFilter method to IDataTransformer and integrate it in getMany for filter transformation

packages/core-api/src/data-services/base-data.transformer.ts

@@ -75,6 +75,12 @@ export interface IDataTransformer<TEntity extends BaseEntity = BaseEntity, TDTO
    * If not provided, falls back to `transformToDTO`.
    */
   transformEditPayload?(entity: Partial<TEntity>): Partial<TDTO>;
+
+  /**
+   * Transform the filter payload before a `getMany()` call.
+   * If not provided, falls back to identity.
+   */
+  transformPayloadFilter?(filter: Record<string, any>): Record<string, any>;
 }
 
 // ─── Abstract Base Transformer ──────────────────────────────────
@@ -213,4 +219,17 @@ export abstract class BaseDataTransformer<TEntity extends BaseEntity = BaseEntit
   transformEditPayload(entity: Partial<TEntity>): Partial<TDTO> {
     return this.transformToDTO(entity as TEntity) as Partial<TDTO>;
   }
+
+  /**
+   * Transform the filter payload before a `getMany()` call.
+   *
+   * Override this when getMany filters need special formatting
+   * (e.g., date formats, converting arrays to comma-separated strings).
+   *
+   * @param filter - The filter params from the frontend
+   * @returns The mapped filter params for the API query
+   */
+  transformPayloadFilter(filter: Record<string, any>): Record<string, any> {
+    return filter;
+  }
 }