Entity Framework Migrations Explained

Database Migrations with Entity Framework Core

James Montemagno is joined by Brice Lambson on the On.Dot Net podcast to discuss entity framework core migrations.
Brice Lambson is a member of the EF Core team and has been working on migrations for almost 12 years.
Entity Framework Core (EF Core) is a popular option for database schema migrations, allowing developers to evolve the schema as their application evolves.
Migrations are similar to version control for source code, allowing developers to record and share changes made to the database schema.
Everyday development and deployment scenarios are common use cases for migrations, such as adding new fields or changing data types.

Understanding Database Migrations in Entity Framework Core

Migrations are necessary when updating databases to a new version while preserving existing data.
SQLite Dash Net is a library that automates additive changes in databases, making it seamless for developers.
However, when more complex changes like splitting a column arise, a migrations framework like Fluent Migrator becomes necessary.
Entity Framework Core (EF Core) is commonly used in web development for its built-in tools and scaffolding.
Before diving into migrations, it's important to consider if it is the right tool for your workflow.
If you prefer crafting databases by hand using SQL or utilizing SQL server projects, migrations may not be necessary.
SQL server projects have a schema feature that allows changes to be made directly to the database.
For developers who enjoy a "database first" workflow, where the database serves as the source of truth, migrations are a suitable choice.

Overview of a Console App using Entity Framework

Entity Framework is a tool that allows users to apply SQL scripts to a database through a console app.
It simplifies the process of running scripts one by one and ensures they run in the correct order.
Entity Framework supports a code-first approach, where the code becomes the source of truth for the database schema.
Users can make changes to their domain model in the application code and generate migrations to update the database.
Reverse engineering or scaffolding can be used when the database is the source of truth, allowing changes to be made to the database and then generating the corresponding code model.
Entity Framework works in various project types, including.NET MAUI, Android apps, and Blazor WebAssembly.
The entry point into the database is the DbContext class, which is responsible for interacting with the database.
DBSets within the DbContext class map to tables in the database.

Creating and Initializing a Database in Entity Framework

Context is used to start a unit of work and make changes to or retrieve data from the database.
Save changes in Entity Framework wraps all changes made in a single transaction.
SQL Lite is used as the database provider in this example, but Entity Framework works with various databases.
The database is created by running a migration, which is done using the NuGet package manager console or by right-clicking on the solution and managing packages.
The initial migration creates the schema of the database based on the current state of the application.

Adding a migration and understanding its anatomy in Visual Studio.

The user is confused about the term "migration" and its purpose.
The user installs a tools package in their CS project to add commands for migrations.
There are different ways to work with migrations, including using the command line or PowerShell.
The user adds a migration called "InitialCreate" which is like a commit message.
A migrations folder is created with the timestamped migration file.
The migration file contains an "up" method and a "down" method.
The "up" method brings the database up to date with the migration's model.
The migration file uses a DSL that resembles SQL but is C# based.
The user creates a table with columns like Id, Title, and Content.

Anatomy of a Migration in Entity Framework

The down method in a migration is used to undo the changes made by the migration.
The drop method in a migration is used to delete a table and its data from the database schema.
The methods in a migration are helper methods that can be called to perform specific actions.
Calling the create method in a migration does not actually create a table, but rather tells Entity Framework to generate SQL for creating a table.
Entity Framework has conventions that can automatically handle certain aspects of the database schema, such as auto-incrementing primary keys.
The designer file in a migration contains a snapshot of the model and is used to provide additional information when generating SQL.
The model snapshot is another snapshot of the model and is used in specific scenarios, such as when altering a column in SQLite.

Anatomy of a Migration and Removing Migrations

Migrations are used to keep track of changes to the database model over time.
Each migration represents a snapshot of the model at a specific point in time.
Migrations are created using the "add migration" command, which generates an up and down method for the changes between the snapshot and the current model.
The "remove migration" command can be used to undo the last migration while keeping the snapshot and other migrations in sync.
Changes to the model can be made using data annotations or by overriding the "on model creating" method.
Data annotations are simpler to use but can make the model less like a POCO (Plain Old CLR Object).
There is no right or wrong way to make changes to the model, as different developers have different preferences.

Creating and Updating a Database with Entity Framework

The title column in the database is not nullable and must have a value specified.
It is generally not recommended to edit these files directly, as it may cause inconsistencies with the entity framework model.
However, it is possible to make changes to the files that align with the existing classes in the model.
The Update Database command is used to create and update the database based on the applied migrations.
The database is created locally in the directory.
The SQLite toolbox can be used to inspect the SQLite database and view the created tables.
EF uses a special table with double underscores to keep track of applied migrations.
The Update Database command generates and executes SQL commands to create tables and apply migrations.
There is no need to call the migration in code once it has been executed through the Update Database command.

Using Migrations in Database Management

Running the app to check if migrations are applied.
Deleting the database and trying the migration process again.
Making changes to the application code and adding a new migration.
The benefits of using package manager console commands.
Adding a new column to the table using migrations.
Applying the migration to the database and checking if the column is added.
Considering the implications of removing a migration that has already been applied.
Adding another migration instead of removing a previously applied migration to maintain synchronization.
Using version control mentality to ensure correct usage of migrations.

Using Migrations in Different Scenarios

For client development, it is safe to apply migrations during app start to upgrade the local database.
This can be done by using the command "db.database.Migrate" in the app.
However, for server scenarios with multiple nodes accessing the same database, applying migrations during app start can cause issues.
In such cases, it is recommended to generate a SQL script using the "script-migration" command.
The generated script can be reviewed by DBAs and become part of the deployment process.
Additional information on using migrations can be found in the documentation at docs.microsoft.com/ef.

Summary of the conversation and closing remarks

The speaker encourages viewers to explore various extensions available on platforms like Docs and YouTube.
Visual Studio and Command-line tools are recommended for use.
The speaker expresses gratitude to Brice for the informative session.
Viewers are invited to leave any questions, especially related to EF Core and Database Migrations, in the comments.

Entity Framework Migrations Explained

Database Migrations with Entity Framework Core

Understanding Database Migrations in Entity Framework Core

Overview of a Console App using Entity Framework

Creating and Initializing a Database in Entity Framework

Adding a migration and understanding its anatomy in Visual Studio.

Anatomy of a Migration in Entity Framework

Anatomy of a Migration and Removing Migrations

Creating and Updating a Database with Entity Framework

Using Migrations in Database Management

Using Migrations in Different Scenarios

Summary of the conversation and closing remarks

Understanding Entity Framework Core Migrations

Overview of Database Migrations in Entity Framework Core