fix: Server crashes due to insufficient schema validation when schema type is not a string

spec/MongoSchemaCollectionAdapter.spec.js

@@ -96,4 +96,111 @@ describe('MongoSchemaCollection', () => {
     });
     done();
   });
+
+  describe('mongoFieldToParseSchemaField function', () => {
+    // Test successful type conversions
+    it('should convert valid mongo field types to parse schema fields', () => {
+      const testCases = [
+        { input: 'string', expected: { type: 'String' } },
+        { input: 'number', expected: { type: 'Number' } },
+        { input: 'boolean', expected: { type: 'Boolean' } },
+        { input: 'date', expected: { type: 'Date' } },
+        { input: 'map', expected: { type: 'Object' } },
+        { input: 'object', expected: { type: 'Object' } },
+        { input: 'array', expected: { type: 'Array' } },
+        { input: 'geopoint', expected: { type: 'GeoPoint' } },
+        { input: 'file', expected: { type: 'File' } },
+        { input: 'bytes', expected: { type: 'Bytes' } },
+        { input: 'polygon', expected: { type: 'Polygon' } },
+        { input: '*_User', expected: { type: 'Pointer', targetClass: '_User' } },
+        { input: '*Post', expected: { type: 'Pointer', targetClass: 'Post' } },
+        { input: 'relation<_User>', expected: { type: 'Relation', targetClass: '_User' } },
+        { input: 'relation<Post>', expected: { type: 'Relation', targetClass: 'Post' } },
+      ];
+
+      testCases.forEach(({ input, expected }) => {
+        const result = MongoSchemaCollection._TESTmongoSchemaToParseSchema({
+          _id: 'TestClass',
+          testField: input,
+        });
+
+        expect(result.fields.testField).toEqual(expected);
+      });
+    });
+
+    // Test error handling for invalid types (non-string values)
+    it('should throw error for invalid field types', () => {
+      const invalidInputs = [
+        null,
+        undefined,
+        123,
+        true,
+        false,
+        {},
+        [],
+        '',
+      ];
+
+      invalidInputs.forEach(invalidInput => {
+        expect(() => {
+          MongoSchemaCollection._TESTmongoSchemaToParseSchema({
+            _id: 'TestClass',
+            testField: invalidInput,
+          });
+        }).toThrow();
+      });
+    });
+
+    it('should throw error with correct message for null input', () => {
+      try {
+        MongoSchemaCollection._TESTmongoSchemaToParseSchema({
+          _id: 'TestClass',
+          testField: null,
+        });
+      } catch (error) {
+        expect(error.code).toBe(255);
+        expect(error.message).toContain('Invalid field type');
+        expect(error.message).toContain('Expected a string');
+      }
+    });
+
+    it('should throw error with correct message for undefined input', () => {
+      try {
+        MongoSchemaCollection._TESTmongoSchemaToParseSchema({
+          _id: 'TestClass',
+          testField: undefined,
+        });
+      } catch (error) {
+        expect(error.code).toBe(255);
+        expect(error.message).toContain('Invalid field type');
+        expect(error.message).toContain('Expected a string');
+      }
+    });
+
+    it('should throw error with correct message for non-string input', () => {
+      try {
+        MongoSchemaCollection._TESTmongoSchemaToParseSchema({
+          _id: 'TestClass',
+          testField: 123,
+        });
+      } catch (error) {
+        expect(error.code).toBe(255);
+        expect(error.message).toContain('Invalid field type');
+        expect(error.message).toContain('Expected a string');
+      }
+    });
+
+    it('should throw error with correct message for empty string input', () => {
+      try {
+        MongoSchemaCollection._TESTmongoSchemaToParseSchema({
+          _id: 'TestClass',
+          testField: '',
+        });
+      } catch (error) {
+        expect(error.code).toBe(255);
+        expect(error.message).toContain('Invalid field type');
+        expect(error.message).toContain('Expected a string');
+      }
+    });
+  });
 });

src/Adapters/Storage/Mongo/MongoSchemaCollection.js

@@ -1,7 +1,15 @@
 import MongoCollection from './MongoCollection';
 import Parse from 'parse/node';
 
-function mongoFieldToParseSchemaField(type) {
+function mongoFieldToParseSchemaField(type, fieldName, className) {
+  // Add type validation to prevent TypeError
+  if (!type || typeof type !== 'string') {
+    throw new Parse.Error(
+      Parse.Error.INVALID_SCHEMA_OPERATION,
+      `Invalid field type: ${type} for field '${fieldName}' in class '_SCHEMA' (id: ${className}). Expected a string. Fix the type mismatch in your schema configuration.`
+    );
+  }
+
   if (type[0] === '*') {
     return {
       type: 'Pointer',
@@ -43,7 +51,7 @@ const nonFieldSchemaKeys = ['_id', '_metadata', '_client_permissions'];
 function mongoSchemaFieldsToParseSchemaFields(schema) {
   var fieldNames = Object.keys(schema).filter(key => nonFieldSchemaKeys.indexOf(key) === -1);
   var response = fieldNames.reduce((obj, fieldName) => {
-    obj[fieldName] = mongoFieldToParseSchemaField(schema[fieldName]);
+    obj[fieldName] = mongoFieldToParseSchemaField(schema[fieldName], fieldName, schema._id);
     if (
       schema._metadata &&
       schema._metadata.fields_options &&