Using the Validation Framework

One of the most important aspects of the mongoose module is validation against a defined model. Mongoose provides a built-in validation framework that only requires you to define validation functions to perform on specific fields that need to be validated. When you try to create a new instance of a document, read a document from the database or save a document, the validation framework calls your custom validation methods and returns an error if the validation fails.

The validation framework is actually very simple to implement. You call the validate() method on the specific path in the Model object that you want to apply validation to and pass in a validation function. The validation function accepts the value of the field and then uses that value to return true or false, depending on whether the value is valid. The second parameter to the validate() method is an error string that is applied to the error object if validation fails. For example:

Click here to view code image

Words.schema.path('word').validate(function(value){
  return value.length < 20;
}, "Word is Too Big");

The error object thrown by validation has the following fields:

error.errors.<field>.message: String defined when adding the validate function

error.errors.<field>.type: Type of validation error

error.errors.<field>.path: Path in the object that failed validation

error.errors.<field>.value: Value that failed validation

error.name: Error type name

err.message: Error message

Listing 16.11 shows a simple example of adding validation to the word model where a word of length 0 or greater than 20 is invalid. Notice that when the newWord is saved in line 18, an error is passed to the save() function. The output in lines 12–26 shows the various values of different parts of the error, as shown in Figure 16.11. You can use these values to determine how to handle validation failures in the code.

Listing 16.11 mongoose_validation.js: Implementing validation of documents in the model by using Mongoose

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01 var mongoose = require('mongoose'),
02 var db = mongoose.connect('mongodb://localhost/words'),
03 var wordSchema = require('./word_schema.js').wordSchema;
04 var Words = mongoose.model('Words', wordSchema);
05 Words.schema.path('word').validate(function(value){
06   return value.length > 0;
07 }, "Word is Too Small");
08 Words.schema.path('word').validate(function(value){
09   return value.length < 20;
10 }, "Word is Too Big");
11 mongoose.connection.once('open', function(){
12   var newWord = new Words({
13     word:'supercalifragilisticexpialidocious',
14     first:'s',
15     last:'s',
16     size:'supercalifragilisticexpialidocious'.length,
17   });
18   newWord.save(function (err) {
19     console.log(err.errors.word.message);
20     console.log(String(err.errors.word));
21     console.log(err.errors.word.type);
22     console.log(err.errors.word.path);
23     console.log(err.errors.word.value);
24     console.log(err.name);
25     console.log(err.message);
26     mongoose.disconnect();
27   });
28 });

Figure 16.11 Implementing validation of documents in the model by using Mongoose.