Learn Ruby on Rails Book

ActiveRecord finder methods

In the previous chapter we learnt how we can query a task from the database using the find_by_slug! method.

There are several other methods which we can use to query one or more than one records from database. In this chapter we will take a look at these finder methods.

find

Let's take an example where a task with ID 1 doesn't exist. What happens when we query a task record with ID 1. Before moving on, pause for a moment to think about what will be the output if we query a record which doesn't exist. Will we get a null value for output?

To answer the question, it depends upon the finder_method used to query data. For eg, If we use the find method:

1Task.find(1)

The above command will raise an exception if there doesn't exist a task with ID 1. You can get away with it if you properly handle exceptions in your Rails application. Handling exceptions is always a good thing.

But how do we prevent exceptions? Let's take a look at some other finder_methods to answer that question.

find by

Using find_by is convenient when we are searching for a record using a column of the record.

1Task.find_by(name: "Get Milk")
2Task.find_by(desc: "Get Eggs")

If a record isn't found then the find_by method will return a nil value. Note that the bang version(!) of find_by will raise an exception if no record is found.

1Task.find_by!(name: "Get Milk")
2Task.find_by!(desc: "Get Eggs")

Above commands will raise an exception if no record is found.

where

Active Record allows us to use where to build more complex queries.

1Task.where(name: "Get Milk", user_id: 3).first

Please note that where operation returns ActiveRecord:Relation. Also note that return of where clause could be a collection of records.

finder methods file in Ruby on Rails

Rails has a file named finder_methods which lists a lot of finder methods which are worth taking a look.

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