README.md

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In this lesson, you will learn how to set up validations and constraints for your models in Sequelize. In the to-do application we created, while creating the Database we set up certain constraint for sequelize work with as below.

const Todo = sequelize.define(
  "Todo",
  {
    title: {
      type: DataTypes.STRING,
      allowNull: false,
    },
    dueDate: {
      type: DataTypes.DATEONLY,
    },
    complete: {
      type: DataTypes.BOOLEAN,
      defaultValue: false,
    },
  },
  {
    tableName: "todo",
  }
);

In the sequelize model, we added a constraint of allowNull to be false. This means that when you add a new to-do, it should always have a to-do text associated with it. If not, the database throws an error, which is being sent back to the application from the server.

Validation is a check performed at the JavaScript level. Providing custom validation capabilities can be tricky. We can also use one of the built-in validators provided by Sequelize. If validation fails, no SQL queries are sent to the database.

Constraints, on the other hand, are rules defined at the SQL level. A simple example of a constraint is the allowNull constraint. If the constraint check fails, the database generates an error and Sequelize redirects this error to JavaScript.

Adding Validations

Let us add validations for the to-do model, restricting the query flow itself if the to-do text is empty. Let us also create a validation to restrict a non-informative to-do text by restricting the minimum character limit to 5.

First, let us add the non-null validation. You can implement the same by updating the title attribute of the model with the following code.

title: {
   type: DataTypes.STRING,
   allowNull: false
   validate: {
       notNull: true
   }
}

Next, let us add a validation for making sure the minimum character limit is 5 by adding the len validator.

title: {
   type: DataTypes.STRING,
   allowNull: false
   validate: {
       notNull: true,
       len: 5
   }
}

The len attribute can also be modified to take two values, with both minimum length and maximum length defined.

When the built-in validators are not sufficient for your application, you can even create a custom validator by passing a function as an entry to the validate attribute.

You learn more about all the options available for you to work with here.

See you in the next lesson.