MSDN Documentation

Entity Framework 6

Entity Framework (EF) is a set of technologies in ADO.NET that supports an abstraction layer that helps automate data access in your application. The Object Relational Designer (O/R Designer) included with Visual Studio enables you to visually design an Entity Data Model (EDM) and to generate a C# or Visual Basic code file that represents your object model. This code file can then be used to interact with your database.

Introduction to EF 6

Entity Framework 6 (EF6) is a mature and feature-rich Object-Relational Mapper (ORM) for .NET. It allows developers to work with databases using .NET objects, abstracting away much of the complexities of direct SQL interaction. EF6 builds upon previous versions, offering improved performance, new features, and enhanced extensibility.

Key Features of EF 6

• LINQ to Entities: Query your database using Language Integrated Query (LINQ) with strongly typed objects.
• Migrations: Manage database schema changes over time as your application evolves, ensuring your database stays synchronized with your code.
• Code First, Database First, Model First: Choose the development approach that best suits your project workflow.
• Connection Resiliency: Automatically retries database commands that fail due to transient errors.
• Dependency Injection: EF6 is designed with extensibility in mind, supporting dependency injection patterns.
• Asynchronous Operations: Improved support for asynchronous database operations, enhancing application responsiveness.

Getting Started with EF 6

To start using EF 6, you typically need to:

1. Install the EF 6 NuGet package: Use the NuGet Package Manager in Visual Studio to install EntityFramework.
2. Define your data model: Create .NET classes that represent your database entities.
3. Create a DbContext: A DbContext class represents a session with the database and allows you to query and save data.
4. Configure your database connection: Specify how EF should connect to your database, often via a connection string in your application's configuration file.

Code First Development

With the Code First approach, you start by defining your domain-specific model classes in C# or VB.NET. EF 6 then automatically creates the database schema based on your classes. This is a popular choice for new projects or when you want to focus on the application's domain logic first.

public class Blog
{
    public int BlogId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Post> Posts { get; set; }
}

public class Post
{
    public int PostId { get; set; }
    public string Title { get; set; }
    public string Content { get; set; }
    public int BlogId { get; set; }
    public virtual Blog Blog { get; set; }
}

public class BloggingContext : DbContext
{
    public DbSet<Blog> Blogs { get; set; }
    public DbSet<Post> Posts { get; set; }

    // Connection string configuration (example)
    public BloggingContext() : base("name=MyConnectionString") {}
}
            

Database First Development

In the Database First approach, you start with an existing database. EF 6's tools can then generate an EDM and C# or VB.NET classes that map to your database schema. This is useful when working with legacy databases or when you have a pre-defined database schema.

Model First Development

Model First development allows you to visually design your data model using the Entity Data Model Designer in Visual Studio. EF 6 then generates the EDM, and you can choose to either generate the database schema from your model or generate code from the model.

Migrations

EF Migrations is a powerful feature that allows you to evolve your database schema over time. You can write code to define schema changes (e.g., adding a table, modifying a column) and apply these changes to your database automatically. This ensures that your database schema remains in sync with your EF model.

Advanced Topics

• Customizing EF Behavior
• Advanced LINQ Querying
• Concurrency Control
• Interceptors
• Stored Procedure Mapping

Performance Considerations

While EF 6 simplifies data access, it's essential to consider performance. Techniques such as eager loading, explicit loading, lazy loading, and optimizing LINQ queries can significantly impact application performance. Profiling your database queries is crucial.

Troubleshooting Common Issues

Common issues include:

• Lazy Loading Exceptions: Ensure your context is still active when accessing related data if lazy loading is enabled.
• Performance Bottlenecks: Review your queries and loading strategies.
• Migration Conflicts: Carefully manage migration files and resolve conflicts.