Explain the concept of CRUD operations in Ruby on Rails and how they are performed using ActiveRecord.

CRUD is an acronym that stands for Create, Read, Update, and Delete. It represents the basic operations performed on data in a database. In the context of Ruby on Rails, these operations are typically performed using ActiveRecord, the object-relational mapping (ORM) library included in Rails.

1. Create: The create operation involves inserting new records or objects into the database. In Rails, creating a new record involves instantiating a new ActiveRecord model object and assigning values to its attributes. Once the object is created, calling the `save` or `create` method on the object will persist it to the database. For example:

```
ruby`# Create a new instance of a model
post = Post.new(title: 'New Post', content: 'Lorem ipsum')

# Save the record to the database
post.save`
```
2. Read: The read operation involves retrieving data from the database. ActiveRecord provides a set of methods to query the database and retrieve records. Common methods include `find`, `where`, `select`, and `all`. These methods generate SQL queries based on the provided parameters and return the matching records as ActiveRecord objects. For example:

```
ruby`# Retrieve a single record by its ID
post = Post.find(1)

# Retrieve all records
posts = Post.all

# Retrieve records that match certain conditions
posts = Post.where(category: 'Technology')`
```
3. Update: The update operation involves modifying existing records in the database. In Rails, you can update a record by loading it from the database, modifying its attributes, and calling the `save` method to persist the changes. Alternatively, you can use the `update` method to update attributes directly without explicitly loading the record. For example:

```
ruby`# Update a record by loading it, modifying attributes, and saving
post = Post.find(1)
post.title = 'Updated Title'
post.save

# Update a record directly using the update method
Post.update(1, title: 'Updated Title')`
```
4. Delete: The delete operation involves removing records from the database. In Rails, you can delete a record by loading it from the database and calling the `destroy` method. Alternatively, you can use the `destroy` method directly on the model class to delete records based on specified conditions. For example:

```
ruby`# Delete a single record by loading and destroying it
post = Post.find(1)
post.destroy

# Delete multiple records based on conditions
Post.destroy_all(category: 'Technology')`
```
These CRUD operations are the building blocks for manipulating data in a Ruby on Rails application. ActiveRecord abstracts the underlying database interactions, allowing developers to work with Ruby objects and methods instead of writing raw SQL queries. This simplifies the database operations and provides a consistent and intuitive interface for working with data in Rails applications.