In operator

src-ui/src/app/components/common/custom-fields-query-dropdown/custom-fields-query-dropdown.component.html

@@ -81,6 +81,15 @@
       @case (CustomFieldQueryOperator.Contains) {
         <pngx-input-document-link [(ngModel)]="atom.value" class="w-25 form-select doc-link-select p-0" placeholder="Search docs..." i18n-placeholder [minimal]="true"></pngx-input-document-link>
       }
+      @case (CustomFieldQueryOperator.In) {
+        <ng-select
+          class="paperless-input-select rounded-end"
+          [items]="getSelectOptionsForField(atom.field)"
+          [(ngModel)]="atom.value"
+          [disabled]="disabled"
+          [multiple]="true"
+        ></ng-select>
+      }
       @default {
         <input class="w-25 form-control rounded-end" type="text" [(ngModel)]="atom.value" [disabled]="disabled">
       }

src-ui/src/app/components/common/custom-fields-query-dropdown/custom-fields-query-dropdown.component.scss

@@ -11,6 +11,13 @@
   height: 100% !important;
 }
 
+::ng-deep .rounded-end .ng-select-container {
+  border-top-right-radius: var(--bs-border-radius) !important;
+  border-bottom-right-radius: var(--bs-border-radius) !important;
+  border-top-left-radius: 0 !important;
+  border-bottom-left-radius: 0 !important;
+}
+
 ::ng-deep .ng-select {
   max-width: 100px;
   min-width: 35%;

src-ui/src/app/components/common/custom-fields-query-dropdown/custom-fields-query-dropdown.component.ts

@@ -252,4 +252,12 @@ export class CustomFieldsQueryDropdownComponent {
       label: CUSTOM_FIELD_QUERY_OPERATOR_LABELS[operator],
     }))
   }
+
+  getSelectOptionsForField(fieldID: number): string[] {
+    const field = this.customFields.find((field) => field.id === fieldID)
+    if (field) {
+      return field.extra_data['select_options']
+    }
+    return []
+  }
 }

src-ui/src/app/data/custom-field-query.ts

@@ -116,7 +116,7 @@ export const CUSTOM_FIELD_QUERY_VALUE_TYPES_BY_OPERATOR = {
   [CustomFieldQueryOperator.GreaterThan]: 'number',
   [CustomFieldQueryOperator.LessThan]: 'number',
   [CustomFieldQueryOperator.Contains]: 'array',
-  // [CustomFieldQueryOperator.In]: 'array', // TODO: Implement
+  [CustomFieldQueryOperator.In]: 'array',
 }
 
 export const CUSTOM_FIELD_QUERY_MAX_DEPTH = 4