fix(discriminator): make base schema paths come before discriminator …

…schema paths when running setters, validators, etc.

Fix #13794

lib/helpers/discriminator/mergeDiscriminatorSchema.js

@@ -34,7 +34,8 @@ module.exports = function mergeDiscriminatorSchema(to, from, path, seen) {
         key === 'base' ||
         key === '_applyDiscriminators' ||
         key === '_userProvidedOptions' ||
-        key === 'options') {
+        key === 'options' ||
+        key === 'tree') {
         continue;
       }
     }

lib/helpers/model/discriminator.js

@@ -116,6 +116,7 @@ module.exports = function discriminator(model, name, schema, tiedValue, applyPlu
     }
 
     mergeDiscriminatorSchema(schema, baseSchema);
+    schema.tree = Object.assign({}, baseSchema.tree, schema.tree);
 
     // Clean up conflicting paths _after_ merging re: gh-6076
     for (const conflictingPath of conflictingPaths) {

test/model.discriminator.test.js

@@ -2180,4 +2180,27 @@ describe('model', function() {
     assert.ok(innerBuildingsPath.schemaOptions.type.discriminators.Garage);
     assert.equal(innerBuildingsPath.schemaOptions.type.discriminators.Garage.discriminatorMapping.value, 'G');
   });
+
+  it('runs base schema paths validators and setters before child schema validators and setters (gh-13794)', async function() {
+    const baseSchema = new Schema({
+      f1: {
+        type: Number,
+        set() {
+          return 1;
+        }
+      }
+    });
+    const childSchema = new Schema({
+      f2: {
+        type: Number,
+        set() {
+          return this.f1;
+        }
+      }
+    });
+    const Test = db.model('Test', baseSchema);
+    const Child = Test.discriminator('Child', childSchema);
+    const doc = new Child({ f1: 2, f2: 2 });
+    assert.strictEqual(doc.f2, 1);
+  });
 });

test/types/schema.test.ts

@@ -1217,4 +1217,4 @@ function gh13800() {
     expectType<string>(this.lastName);
     expectError<string>(this.someOtherField);
   });
-}
+}