docs(validation): add section on global schematype validation, clean up other issues

docs/validation.md

@@ -15,6 +15,20 @@ Before we get into the specifics of validation syntax, please keep the following
 [require:Validation$]
 ```
 
+- [Built-in Validators](#built-in-validators)
+- [Custom Error Messages](#custom-error-messages)
+- [The `unique` Option is Not a Validator](#the-unique-option-is-not-a-validator)
+- [Custom Validators](#custom-validators)
+- [Async Custom Validators](#async-custom-validators)
+- [Validation Errors](#validation-errors)
+- [Cast Errors](#cast-errors)
+- [Global SchemaType Validation](#global-schematype-validation)
+- [Required Validators On Nested Objects](#required-validators-on-nested-objects)
+- [Update Validators](#update-validators)
+- [Update Validators and `this`](#update-validators-and-this)
+- [Update Validators Only Run On Updated Paths](#update-validators-only-run-on-updated-paths)
+- [Update Validators Only Run For Some Operations](#update-validators-only-run-for-some-operations)
+
 ### Built-in Validators
 
 Mongoose has several built-in validators.
@@ -107,6 +121,15 @@ fails. That means your custom validators may assume `v` is `null`,
 [require:Cast Errors]
 ```
 
+### Global SchemaType Validation
+
+In addition to defining custom validators on individual schema paths, you can also configure a custom validator to run on every instance of a given `SchemaType`.
+For example, the following code demonstrates how to make empty string `''` an invalid value for _all_ string paths.
+
+```javascript
+[require:Global SchemaType Validation]
+```
+
 ### Required Validators On Nested Objects
 
 Defining validators on nested objects in mongoose is tricky, because
@@ -148,15 +171,6 @@ not defined.
 [require:Update Validators and `this`]
 ```
 
-### The `context` option
-
-The `context` option lets you set the value of `this` in update validators
-to the underlying query.
-
-```javascript
-[require:The `context` option]
-```
-
 ### Update Validators Only Run On Updated Paths
 
 The other key difference is that update validators only run on the paths
@@ -178,10 +192,10 @@ following update operators:
 
 - `$set`
 - `$unset`
-- `$push` (>= 4.8.0)
-- `$addToSet` (>= 4.8.0)
-- `$pull` (>= 4.12.0)
-- `$pullAll` (>= 4.12.0)
+- `$push`
+- `$addToSet`
+- `$pull`
+- `$pullAll`
 
 For instance, the below update will succeed, regardless of the value of
 `number`, because update validators ignore `$inc`.

test/docs/validation.test.js

@@ -380,6 +380,33 @@ describe('validation docs', function() {
     // acquit:ignore:end
   });
 
+  it('Global SchemaType Validation rray', async function() {
+    // Add a custom validator to all strings
+    mongoose.Schema.Types.String.set('validate', v => v == null || v > 0);
+
+    const userSchema = new Schema({
+      name: String,
+      email: String
+    });
+    // acquit:ignore:start
+    db.deleteModel(/User/);
+    // acquit:ignore:end
+    const User = db.model('User', userSchema);
+
+    const user = new User({ name: '', email: '' });
+
+    const err = await user.validate().then(() => null, err => err);
+    err.errors['name']; // ValidatorError
+    err.errors['email']; // ValidatorError
+    // acquit:ignore:start
+    assert.ok(err);
+    assert.equal(err.errors['name'].name, 'ValidatorError');
+    assert.equal(err.errors['email'].name, 'ValidatorError');
+
+    delete mongoose.Schema.Types.String.defaultOptions;
+    // acquit:ignore:end
+  });
+
   /**
    * Defining validators on nested objects in mongoose is tricky, because
    * nested objects are not fully fledged paths.
@@ -503,42 +530,6 @@ describe('validation docs', function() {
     assert.ok(error);
   });
 
-  /**
-   * The `context` option lets you set the value of `this` in update validators
-   * to the underlying query.
-   */
-
-  it('The `context` option', async function() {
-    // acquit:ignore:start
-    const toySchema = new Schema({
-      color: String,
-      name: String
-    });
-    // acquit:ignore:end
-    toySchema.path('color').validate(function(value) {
-      // When running update validators, `this` refers to the query object.
-      if (this.getUpdate().$set.name.toLowerCase().indexOf('red') !== -1) {
-        return value === 'red';
-      }
-      return true;
-    });
-
-    const Toy = db.model('Figure', toySchema);
-
-    const update = { color: 'blue', name: 'Red Power Ranger' };
-    // Note the context option
-    const opts = { runValidators: true, context: 'query' };
-
-    let error;
-    try {
-      await Toy.updateOne({}, update, opts);
-    } catch (err) {
-      error = err;
-    }
-
-    assert.ok(error.errors['color']);
-  });
-
   /**
    * The other key difference is that update validators only run on the paths
    * specified in the update. For instance, in the below example, because