diff --git a/lib/DataHarmonizer.js b/lib/DataHarmonizer.js
index 1bc3311e..6023a237 100644
--- a/lib/DataHarmonizer.js
+++ b/lib/DataHarmonizer.js
@@ -776,17 +776,43 @@ class DataHarmonizer {
     // Get the starting row index where the new rows will be added
     const startRowIndex = this.hot.countRows();
 
-    // Insert the new rows below the last existing row
-    this.hot.alter('insert_row_below', startRowIndex, numRows);
     // Validate and process the current selection
-    if (
-      this.context.currentSelection !== null &&
-      this.context.currentSelection.valueToMatch !== null
-    ) {
-      // Find the nearest index after the last non-empty row in the specified column
-      this.populateNewRows(numRows, startRowIndex);
+    const is1mAndHasParent = (class_assignment) => {
+      console.log(this.context.currentSelection, this.context.oneToManyAppContext.appContext[class_assignment]);
+      const unique_keys = this.context.oneToManyAppContext.appContext[class_assignment].unique_keys;
+      for (let key in unique_keys) {
+        if ('foreign_key' in unique_keys[key]) {
+          return unique_keys[key].foreign_key;
+        }
+      }
+      return false;
+    };
+    const classIsForeignKeyForClassAndCurrentSelection = (maybe_child_class, currentSelection) => {
+      const unique_keys = this.context.oneToManyAppContext.appContext[maybe_child_class].unique_keys;
+      return !isEmptyUnitVal(unique_keys[currentSelection.shared_key_name]) && maybe_child_class !== currentSelection.source;
+
+    }
+    // check if the DH refers to a parent class or class with no children.
+    // if it has a parent, ensure a foreign key is selected in some parent
+    // if it doesn't have a parent, use regular add rows implementation
+    if (is1mAndHasParent(this.class_assignment)) {
+      if (
+        !isEmptyUnitVal(this.context.currentSelection) &&
+        !isEmptyUnitVal(this.context.currentSelection.valueToMatch) &&
+        classIsForeignKeyForClassAndCurrentSelection(this.class_assignment, this.context.currentSelection)
+      ) {
+
+        // Insert the new rows below the last existing row
+        this.hot.alter('insert_row_below', startRowIndex, numRows);
+        // Find the nearest index after the last non-empty row in the specified column
+        this.populateNewRows(numRows, startRowIndex);
+      } else {
+        console.warn('No current selection to populate the new rows.');
+        $('#empty-parent-key-modal').modal('show');
+      }
     } else {
-      console.warn('No current selection to populate the new rows.');
+      // Insert the new rows below the last existing row
+      this.hot.alter('insert_row_below', startRowIndex, numRows);
     }
   }
 
diff --git a/lib/Toolbar.js b/lib/Toolbar.js
index b69031f2..7f16b1b6 100644
--- a/lib/Toolbar.js
+++ b/lib/Toolbar.js
@@ -35,6 +35,7 @@ import pkg from '../package.json';
 
 const VERSION = pkg.version;
 
+
 class Toolbar {
   constructor(root, context, options = {}) {
     this.context = context;