EF Core Notes (Cheat Sheet)

Here's a structured post for your EF Core Notes (Interactive/Cheat Sheet) with code snippets and details:

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1. Required NuGet Packages

Data Access Layer (DAL):

• Microsoft.EntityFrameworkCore.SqlServer

• Microsoft.EntityFrameworkCore.Tools

API/MVC Project:

• Microsoft.EntityFrameworkCore.Design

2. Configuring the DbContext

protected override void OnConfiguring(DbContextOptionsBuilder options)
{
    options.UseSqlServer("Server=(LocalDb)\\MSSQLLocalDB;Database=CodingWiki;TrustServerCertificate=True;Trusted_Connection=True;");
}

3. Renaming a Column

• Change property name in entity.

• Migrations:

  • Add-Migration RenameColumn

  • Update-Database

4. Seeding Data Through Migration

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // Precision
    modelBuilder.Entity<Book>()
        .Property(b => b.Price)
        .HasPrecision(10, 5);

    // Seed data
    modelBuilder.Entity<Book>().HasData(
        new Book { BookId = 1, Title = "Spider without Duty", ISBN = "123B12", Price = 10.99m }
        // ... more
    );
}

5. Typical Workflow

• Code changes (add/update/seed, etc.)

• Run:

  • Add-Migration <Name>

  • Update-Database

6. Example Entity

public class Book
{
    public int BookId { get; set; }
    public string Title { get; set; }
    public string ISBN { get; set; }
    public decimal Price { get; set; }
}

7. Register Table

public DbSet<Book> Books { get; set; }

Entity Relationships & Data Annotations

1. Common Data Annotations

2. Entity Relationship Examples

One-to-One

public class Book
{
    public int BookId { get; set; }
    public BookDetail BookDetail { get; set; }
}

public class BookDetail
{
    [Key]
    public int BookDetail_Id { get; set; }
    [ForeignKey("Book")]
    public int Book_Id { get; set; }
    public Book Book { get; set; }
}

One-to-Many

public class Publisher
{
    [Key]
    public int Publisher_Id { get; set; }
    public List<Book> Books { get; set; }
}

public class Book
{
    [ForeignKey("Publisher")]
    public int Publisher_Id { get; set; }
    public Publisher Publisher { get; set; }
}

Many-to-Many (with mapping entity)

public class Author { ... public List<BookAuthorMap> BookAuthorMap { get; set; } }
public class Book   { ... public List<BookAuthorMap> BookAuthorMap { get; set; } }

public class BookAuthorMap
{
    [ForeignKey("Book")] public int Book_Id { get; set; }
    [ForeignKey("Author")] public int Author_Id { get; set; }
    public Book Book { get; set; }
    public Author Author { get; set; }
}

// Join with composite key
modelBuilder.Entity<BookAuthorMap>().HasKey(u => new { u.Author_Id, u.Book_Id });

3. Quick Attribute Summary

• [Key] – Primary key

• [Required] – Not null

• [MaxLength(n)] – String length

• [NotMapped] – Excluded from DB

• [ForeignKey("Name")] – Explicit FK

4. Connection String Example

options.UseSqlServer("Server=(LocalDb)\\MSSQLLocalDB;Database=CodingWiki;TrustServerCertificate=True;Trusted_Connection=True;");

Additional Considerations

• [Table("TableName")] annotation for changing table names.

• [Column("ColName")] for explicit column mapping.

• Indexes: [Index(nameof(PropertyName), IsUnique = true)] (from EF Core 5.0+).

• Fluent configuration: modelBuilder.Entity<Book>().ToTable("Tbl_Books");

• Cascade delete behavior: OnDelete(DeleteBehavior.Cascade)

Sample Additions

Change Table/Column Name

[Table("Tbl_Books")]
public class Book
{
    [Column("Book_ID")]
    public int BookId { get; set; }
    // ...
}

// Or in OnModelCreating:
modelBuilder.Entity<Book>().ToTable("Tbl_Books");
modelBuilder.Entity<Book>().Property(b => b.Title).HasColumnName("Book_Title");

Index Example

[Index(nameof(ISBN), IsUnique = true)]
public class Book { ... }

Cascade Delete Example

modelBuilder.Entity<Book>()
    .HasOne(b => b.Publisher)
    .WithMany(p => p.Books)
    .HasForeignKey(b => b.Publisher_Id)
    .OnDelete(DeleteBehavior.Restrict);

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This cheat sheet provides a comprehensive guide to using EF Core effectively, with examples and annotations to help streamline your development process.