feat: Add custom error message for minlength validation errors. (#212)

lib/Value.ts

@@ -1,4 +1,5 @@
 import Ajv from 'ajv';
+import { getByDataPath } from './getByDataPath';
 import { JSONSchema7 } from 'json-schema';
 import { ValidationError } from './ValidationError';
 
@@ -27,6 +28,7 @@ class Value {
     }
 
     const error = this.validateInternal.errors![0];
+    const failingValue = getByDataPath({ object: value, dataPath: error.dataPath });
 
     let updatedPath = `${valueName}${error.dataPath.replace(/\//gu, separator)}`;
     let message = 'Validation failed';
@@ -50,6 +52,15 @@ class Value {
         break;
       }
 
+      case 'minLength': {
+        const minPropertyLength = (error.params as Ajv.LimitParams).limit;
+        const actualLength = failingValue.length;
+
+        message = `String is too short (${actualLength} chars), minimum ${minPropertyLength}`;
+
+        break;
+      }
+
       default: {
         // Intentionally left blank.
       }

lib/getByDataPath.ts

@@ -0,0 +1,18 @@
+const getByDataPath = function ({ object, dataPath }: { object: any; dataPath: string }): any {
+  const pathSegments = dataPath.split('.');
+  const nonEmptyPathSegments = pathSegments.filter((segment): boolean => segment !== '');
+
+  let value = object;
+
+  for (const pathSegment of nonEmptyPathSegments) {
+    if (value === undefined) {
+      break;
+    }
+
+    value = value[pathSegment];
+  }
+
+  return value;
+};
+
+export { getByDataPath };

test/unit/ValueTests.ts

@@ -123,6 +123,23 @@ suite('Value', (): void => {
           });
         }).is.throwing((ex: Error): boolean => ex.message === 'Unexpected additional property: login (at value.login).');
       });
+
+      test('throws an error if a string undercuts a minimum length.', async (): Promise<void> => {
+        schema = new Value({
+          type: 'object',
+          properties: {
+            username: { type: 'string', minLength: 4 }
+          },
+          required: [ 'username' ],
+          additionalProperties: false
+        });
+
+        assert.that((): void => {
+          schema.validate({
+            username: 'foo'
+          });
+        }).is.throwing((ex: Error): boolean => ex.message === 'String is too short (3 chars), minimum 4 (at value.username).');
+      });
     });
   });
 

test/unit/getByDataPathTests.ts

@@ -0,0 +1,34 @@
+import { assert } from 'assertthat';
+import { getByDataPath } from '../../lib/getByDataPath';
+
+suite('getByDataPath', (): void => {
+  test('traverses an object by following an ajv data path.', async (): Promise<void> => {
+    const object = {
+      foo: {
+        bar: {
+          baz: 'bam'
+        }
+      }
+    };
+
+    const result = getByDataPath({ object, dataPath: '.foo.bar.baz' });
+
+    assert.that(result).is.equalTo('bam');
+  });
+
+  test('returns undefined, if the path does not match anything.', async (): Promise<void> => {
+    const object = {};
+
+    const result = getByDataPath({ object, dataPath: '.foo.bar.baz' });
+
+    assert.that(result).is.undefined();
+  });
+
+  test('returns undefined, if the object is undefined.', async (): Promise<void> => {
+    const object = undefined;
+
+    const result = getByDataPath({ object, dataPath: '.foo.bar.baz' });
+
+    assert.that(result).is.undefined();
+  });
+});