What is the difference between .save and .create in Sequelizejs?

In Sequelize.js, both the .save() and .create() methods can be used to save data entities to the database, but their usage scenarios and behaviors differ.

.create() Method

The .create() method is typically used to create and save a new entity to the database. When you have a data object and wish to add it as a new record to the table, using .create() is the most straightforward approach. This method accepts an object (representing the attributes of a model) and returns a model instance representing the newly inserted record.

Example: Suppose we have a User model, and we want to create a new user:

javascript
const newUser = await User.create({
  username: 'johndoe',
  email: 'john@example.com'
});

In this example, Sequelize automatically handles the SQL insertion and returns a User instance representing the newly created record.

.save() Method

Compared to .create(), the .save() method is used to save a model instance, whether it is new or already exists. If the instance is new (i.e., no corresponding database record exists), Sequelize executes an INSERT operation; if the instance already exists in the database (i.e., a corresponding record is present), it performs an UPDATE operation.

Example: Using the same User model, but assuming we have already loaded a user instance from the database and modified it:

javascript
const user = await User.findByPk(1);
user.email = 'newemail@example.com';
await user.save();

In this example, the save() method checks if the user instance exists in the database. Since it is an already loaded instance, it executes an UPDATE operation to modify the user's email address.

Summary

• Use .create() to create and save a brand-new record.
• Use .save() to save a model instance, which can be new or existing, depending on the instance's state.

In practical applications, choosing between .create() and .save() depends on your specific requirements and context.