added unit to ingredient with constraint

src/Plugin/Asset/AssetType/Ingredient.php

@@ -32,7 +32,17 @@ class Ingredient extends FarmAssetType {
             'amount_field' => [
                 'type' => 'fraction',
                 'label' => $this->t('Amount'),
-                'description' => $this->t('How much of the chemical is in the ingredient in g/l'),
+                'description' => $this->t('How much of the chemical is in the ingredient'),
+                'required' => TRUE,
+            ],
+            'unit_field' => [
+                'type' => 'entity_reference',
+                'label' => $this->t('Unit'),
+                'description' => $this->t('What unit is the ingredient measured in?'),
+                'target_type' => 'taxonomy_term',
+                'target_bundle' => 'unit',
+                'auto_create' => TRUE,
+                'multiple' => FALSE,
                 'required' => TRUE,
             ],
         ];

src/Plugin/Validation/Constraint/SubstanceIngredientsConstraint.php

@@ -23,5 +23,6 @@ use Symfony\Component\Validator\Constraint;
 final class SubstanceIngredientsConstraint extends Constraint {
     
     public string $notUnique = 'Some chemicals were entered twice.';
+    public string $notTheSameUnit = 'All ingredients need to be measured with the same unit.';
     
 }

src/Plugin/Validation/Constraint/SubstanceIngredientsConstraintValidator.php

@@ -23,15 +23,25 @@ final class SubstanceIngredientsConstraintValidator extends ConstraintValidator
             );
         }
         $seen_quantities = [];
+        $old_unit = null;
         foreach ($items as $delta => $item) {
             $ingredient = \Drupal::entityTypeManager()->getStorage('asset')->load($item->target_id);
             $chemical_id = $ingredient->chemical_field->target_id;
+            $new_unit = $ingredient->unit_field->target_id;
             if (isset($seen_quantities[$chemical_id])) {
                 $this->context->buildViolation($constraint->notUnique)
                 ->atPath($delta)
                 ->addViolation();
             }
+            if (isset($old_unit)) {
+                if ($old_unit != $new_unit) {
+                    $this->context->buildViolation($constraint->notTheSameUnit)
+                    ->atPath($delta)
+                    ->addViolation();
+                }
+            }
             $seen_quantities[$chemical_id] = true;
+            $old_unit = $new_unit;
         }
     }
 }