Entities are the building blocks that make up just about everything on a Drupal site. Regardless of whether entities provide configuration information or content, they are absolutely crucial to Drupal's data model.

In this tutorial we'll:

• Look at the overall class hierarchy between the various entity types to see how they're related.
• Examine differences between configuration and content entities in the code that defines them.
• Look at some of the core code required to create an entity type.

By the end of this lesson you should be able to use an example to create a custom entity type in code.

Often when building a site in Drupal you'll find yourself wanting to display a list of nodes, or find entities created by a particular author, or locate some content based on a particular set of criteria. Rather than querying the database directly, Drupal provides a helper class, EntityQuery, to make things a bit easier. The EntityQuery class will probably look very familiar to you if you're familiar with the Database API, or the EntityFieldQuery class in Drupal 7.

In this tutorial we'll:

• Go through several examples of using EntityQuery to find subsets of content.
• Demonstrate how to iterate over the results of an EntityQuery query.

By the end of this tutorial, you should understand how to use entity queries to create custom sets of data from entities.

When learning Drupal development, it won't be long before you encounter the word "entity" and the Entity API. But what are entities in Drupal? How can you use them to build your site? When should you use the Entity API?

This tutorial will explain Drupal's Entity system from a high level. We'll look at:

• The main problems the Entity system solves
• Key terms you should know
• Key concepts we'll explore as we dive into Drupal's Entity API

By the end of this tutorial you should be able to explain the problems that the Entity API solves, and when you should use it in your own code.

Drupal includes the Symfony Validator component, and provides an Entity Validation API to assist in validating the values of fields on an entity. By using the Entity Validation API you can ensure that you're validation logic is applied to Entity CRUD operations regardless of how they are triggered. Whether editing an Entity via a Form API form, or creating a new Entity via the REST API, the same validation code will be used.

Using the Entity Validation API in order to validate the value of a field on an entity requires:

• Defining (or choosing) a constraint plugin
• Defining (or choosing) a validation plugin
• Adding the constraint to the field definition

In this tutorial, we'll look at how this Validation API works and how it can be used in custom code to ensure our entities have properly constructed values. We'll look at how this validation works in Drupal core and how we can add our own additional constraints. We'll also see how to work with the error messages returned from the validator when our entity doesn't pass validation.

Containers are sandboxed applications that can be run anywhere, no matter the underlying host OS. Docker containers are quite different from VMs in a number of ways that need to be understood before we can use them to develop Drupal sites.

In this tutorial, we'll:

• Define a container
• Explain how a container is a more limited environment than a VM

Media source plugins provide the link between media entities in Drupal and the actual media asset itself. They are the code that understand the difference between an image, a video, and a Tweet, and perform the translation that allows the media ecosystem to treat all media entities equally. For example, local image files, and remote YouTube videos, can both be catalogued in a similar way as media entities, but they need very different handling when it comes to displaying them.

Media sources are represented as plugins, there are a handful in Drupal core, and a developer can add new plugins to represent any type of media your application needs to catalogue.

In this tutorial we'll learn:

• How media source plugins relate to Media Types
• The responsibilities of a media source plugin

By the end of this tutorial you should be able to define the role of a media source plugin and understand what's required to define your own.

The Drupal core Media Library module provides an enhanced user interface for locating Media entities and attaching them to an article. It's a drop-in replacement for the default entity reference widget which uses a not very intuitive autocomplete field. Using the Drupal core Media Library module requires minimal configuration.

If you want to provide content creators with a gallery-like library of Media entities that they can browse through in order to find the ones they want to add to their content, the Media Library is the easiest way to do it. It can be configured to work with both Media fields and the CKEditor powered WYSIWYG editor commonly used for editing the body field of Drupal nodes. There's really no reason not to use it.

In addition to providing a better UI for locating existing Media entities, the Media Library provides a way to create new Media entities right from the content creation form. This prevents an otherwise confusing requirement where Media entities need to be created, via a different set of forms, before they can be used.

In this tutorial we'll:

• Install and configure the Media Library module to work with Media fields
• Use the user interface provided by the Media Library to improve the experience of finding and selecting Media entities to associate with a piece of content

By the end of this tutorial you'll know how to replace the default entity reference widget used for selecting Media entities with the much improved Media Library UI.

Media entities, like any content entity, work great with all the different features Drupal provides for changing the way things are displayed: view modes, Layout Builder, theme templates, and more. We're big fans of using view modes to create a component-like design system where entity types have view modes representing the different context in which they're displayed. Then we theme the view modes. This works great for displaying Media entities associated with a page and for changing the way that Media assets are displayed within the Media Library browser.

In this tutorial we'll:

• Create Hero and Sidebar view modes for Media entities
• Configure the Image Media type to use the new view modes and style each one differently
• Use the new view modes to render Image Media assets within a Layout
• Update the Media library view mode that's used by the Media Library browser to display additional information alongside the thumbnails used when selecting Media to attach to a page

By the end of this tutorial you should be able to change the way that Media assets are displayed by using view modes and display formatters in a Drupal site.

It's not uncommon to patch, or customize, contributed modules during the lifetime of a site. It's important to know if you've done so when planning for a migration since you'll want to be sure that you don't lose any customizations when you start using an updated version of a module.

In this tutorial we will walk through using the Hacked! module to check for any alterations to your Drupal code base.

The Drupal-to-Drupal migration system is still a work in progress. As such, there are a few things that simply don't work, and a few others that still have kinks to be ironed out. In this tutorial, we'll look at some of the common hang-ups that we've encountered, the status of resolving those issues, and what your options are in the meantime.

In Drupal, there are 3 modules in core related to migration that you'll want to know about. These modules can help you import data into Drupal from disparate sources, or upgrade from a previous version of Drupal.

In this tutorial we'll look at what each of these core migration modules do, and talk about when you'll need to use them.

Drupal core provides support for migrating data from Drupal 6 or 7. The templates provided in core migrate your data in a very specific way. They attempt to copy things verbatim whenever possible. However, you may wish to alter this for your migrations. In this tutorial we are going to explore the various ways that you can alter the existing Drupal-to-Drupal migrations to meet your needs.

One method of creating a custom Drupal-to-Drupal migration involves using the Migrate Upgrade module to generate a set of migration configuration entities that you can use as a starting point. Even if you're not going to use the generated output in the end, this is still an informative exercise as it allows you to see examples of various migration paths.

In this tutorial we'll:

• Use the Migrate Upgrade module's Drush commands to import Drupal core's migration templates
• Examine the generated configuration entities
• Use the Migrate Tools module's Drush commands to view a list of the individual migrations that make up our Drupal-to-Drupal migration

By the end of this tutorial, you should be able to use the Migrate Upgrade module to generate the migrations that Drupal core would use to migrate content, list those migrations, and inspect them individually.

If you want to modify the Drupal-to-Drupal migrations created by Migrate Upgrade you'll need to export the Migrate Plus configuration entities, convert the ones you want to customize to standard migration .yml files, and put them into a custom module. Then, you can make edits the YAML definition of the migration, and keep your customizations in Git.

We recommend creating a new module to house the code that makes up your custom Drupal-to-Drupal migration.

In this tutorial we'll:

• Create a new module
• Export the migration configuration entities generated by drush migrate-upgrade as YAML files
• Copy the files that represent the migrations we're interested in into our new module
• Customize the copied files

By the end of this tutorial you should have a new module that contains the starting migration YAML files for your custom migration.

Before we can learn to write a custom migration, we need some sample data and a destination site for that data.

In this tutorial we'll obtain some source data to work with and configure our Drupal destination site by creating the necessary content types and fields to accommodate the source data. Then we'll look at the data that we'll be importing and start to formulate a migration plan.

By the end of this tutorial you'll have some source data and an empty but configured destination Drupal site ready for data import.

As part of creating a custom Drupal-to-Drupal migration we want to limit the set of users that are migrated from our source site into our destination Drupal site. In this tutorial we'll:

• Extend the existing source plugin
• Alter the query that's used to select users from our source site
• Update our user migration to use the new source plugin

By the end of this tutorial you should be able to override the core source plugins used when migrating from prior versions of Drupal in order to gain more control over exactly what is migrated.

Every migration is unique, which means there are loads of great examples you can review and learn from. We'll keep this tutorial up-to-date with our favorites and let you know how we think these examples might help.

In this tutorial we will run a site migration using Drush, and understand how to deal with any failures that occur.

The Migrate Drupal UI module allows you to execute a migration from older versions of Drupal to the latest version of Drupal. In this tutorial we'll:

• Run a full Drupal 6 to latest-Drupal (Drupal 8 or 9) Migration from the UI
• Explore the user interface as it exists
• Understand how we can deal with the output from our migration

Every row returned, from every source, during the execution of a migration is passed through hook_migrate_prepare_row() and hook_migrate_MIGRATION_ID_prepare_row(). Using these two hooks we can augment our migration in a variety of different ways.

In this tutorial we'll:

• Discuss the use case for hook_migrate_prepare_row()
• Implement hook_migrate_prepare_row() and use it to skip all but a select list of fields during the field migration
• Implement hook_migrate_MIGRATION_ID_prepare_row() and use it to skip all but a select list of node types

By the end of this tutorial you should have a better understanding of when hook_migrate_prepare_row() might be useful when writing your own migration, as well as how to skip rows in a migration based on conditional logic.