In this lesson, we'll go over how to query our postgres database utilizing Sequelize, we'll learn and practice how to perform everything from simple crud operation queries to complex filtering. Sequelize is a great ORM that simplifies the querying process by utilizing methods directly built into our models when we create them. The provided code has all of the configuration, models, migrations and seeds created for you.
- Fork and Clone
npm installsequelize db:createsequelize db:migratesequelize db:seed:all
When we define our Sequelize models, you'll notice that the model defined inherites from the Model class provided by Sequelize. This model class has methods and attributes built in to query or manipulate any model that we create. When we invoke these functions, Sequelize executes some SQL query to retrieve the desired information from our database. The queries return a promise by default which means we must wait for them to finish by either using async/await or .then().catch().
Note: Not all queries return the result formatted as you'd expect, make sure to check how the result is formatted!
The findAll method will query a table matching our model and return all results. If a filter is provided, or a where clause, we can filter results where a certain condition is met.
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The findByPk method queries a table to find a result where the primary key, typically an id, is a match.
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The findOne method returns one record at a time, based on a condition. This method is paired with a where clause to filter for specific data points.
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The create method will create a new record in the database with the provided information. Unlike noSql databases, if information is missing or not specified when invoking the create method, the creation will fail and return an error.
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The destroy method will delete a record or records that match the filtering parameters. The filtering parameters or where clause is provided to the first object. The second object is provided some extra options to execute on deletion.
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The update method will update a record or records and return an array with the number of items updated and the records updated. It does not return the records by default, we have to provide the returning:true flag to the method in order to get the results. The first object is the information to update the record or records with, the second being the where clause or filtering to ensure we execute the update on only the desire records.
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Just because Sequelize provides us with methods to execute queries does not mean they are perfect. ORM's are notorious for performing more operations than necessary when querying. If you feel that you can execute a complex query and Sequelize is taking too long, you can write your own!
In the provided queries.js file, you'll create functions to execute several queries, utilize the stringify method provided to print the results to the console.
Write functions to execute the following queries on the Business model:
- Find all businesses
- Find a business by id
- Find a business where the rating is a 5
- Find one business where the rating is a 4
- Create a business
- Update the business you previously created
- Delete the business you created
Once you complete your function, make sure to add it to the try block in the main function at the bottom of the file.
Sequelize is a great ORM that gives us a lot out of the box. ORMS are great tools to speed up our workflow and add in some extra security benefits. There are many more methods that you can use with Sequelize which we'll list below in the Resources Section. As with any new tool, there is a learning curve, but once you pick up the basics the rest just follows the same pattern.